{"product_id":"kieserite-magnesium-sulphate-fertiliser","title":"Kieserite Fertiliser | 25% MgO, 50% SO₃ | Water-Soluble Magnesium","description":"\u003c!-- Dr Forest — Kieserite (Magnesium Sulphate Monohydrate) Shopify Product Page --\u003e\n\u003cp\u003e \u003c\/p\u003e\n\u003c!-- Design System v1.0 · 4-tab layout · prefix \"ks\" · Shopify-safe, no JS --\u003e\n\u003cstyle\u003e\n  .drf-wrap *, .drf-wrap *::before, .drf-wrap *::after { box-sizing: border-box; margin: 0; padding: 0; }\n  .drf-wrap { font-family: 'Jost', sans-serif; font-weight: 400; color: #2c2c2c; font-size: 14px; line-height: 1.65; width: 100%; max-width: 100%; overflow: hidden; }\n  :root {\n    --drf-grn:        #1B3D2F;\n    --drf-grn-dark:   #0F2A1F;\n    --drf-grn-light:  #E8F0EB;\n    --drf-grn-mid:    #4a7a5e;\n    --drf-cream:      #F5F2EC;\n    --drf-gold:       #C5A55A;\n    --drf-gold-light: #FAF7F0;\n    --drf-muted:      #3A4A40;\n    --drf-white:      #FFFFFF;\n    --drf-border:     #d4cfc5;\n  }\n\n  \/* ── TYPOGRAPHY ── *\/\n  .drf-wrap h2 { font-family: 'Cormorant Garamond', serif; 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}\n  .drf-steps li:last-child { border-bottom: none; }\n\n  \/* ── USE-CASE LIST ── *\/\n  .drf-uses { list-style: none; padding: 0; }\n  .drf-uses li { padding: 0.6em 0; border-bottom: 1px solid var(--drf-gold); }\n  .drf-uses li:nth-child(even) { border-bottom-color: var(--drf-grn); }\n  .drf-uses li:last-child { border-bottom: none; }\n  .drf-uses li strong { color: var(--drf-grn-dark); }\n\n  \/* ── COMPARISON BOXES ── *\/\n  .drf-compare { margin: 1.2em 0; }\n  .drf-compare-box { border: 1px solid var(--drf-border); padding: 1em 1.2em; margin-bottom: 0.8em; border-radius: 0; background: var(--drf-grn-light); }\n  .drf-compare-box h4 { margin-top: 0; color: var(--drf-grn-dark); text-transform: none; letter-spacing: 0; font-size: 1.05em; font-family: 'Cormorant Garamond', serif; font-weight: 500; border-bottom: 1px solid var(--drf-gold); padding-bottom: 0.4em; margin-bottom: 0.6em; }\n\n  \/* ── FAQ ACCORDIONS ── *\/\n  .drf-faq { border-bottom: 1px solid var(--drf-border); }\n  .drf-faq:last-child { border-bottom: none; }\n  .drf-faq input[type=\"checkbox\"] { display: none; }\n  .drf-faq-q { display: flex; justify-content: space-between; align-items: center; padding: 0.8em 0; cursor: pointer; font-weight: 500; color: var(--drf-grn-dark); font-size: 0.95em; }\n  .drf-faq-q::after { content: '+'; font-size: 1.2em; font-weight: 300; color: var(--drf-gold); width: 1.5em; height: 1.5em; border-radius: 0; border: 1px solid var(--drf-gold); background: var(--drf-white); display: flex; align-items: center; justify-content: center; flex-shrink: 0; margin-left: 0.6em; }\n  .drf-faq-a { max-height: 0; overflow: hidden; transition: max-height 0.3s ease; font-size: 0.92em; color: var(--drf-muted); line-height: 1.7; }\n  .drf-faq-a \u003e div { padding: 0 0 1em; }\n  .drf-faq input:checked ~ .drf-faq-q::after { content: '\\2212'; background: var(--drf-grn-dark); color: #fff; border-color: var(--drf-grn-dark); }\n  .drf-faq input:checked ~ .drf-faq-a { max-height: 900px; }\n\n  \/* ── REFERENCES ── *\/\n  .drf-refs { font-size: 0.78em; color: #6b7a70; line-height: 1.5; margin-top: 1.5em; padding-top: 0.8em; border-top: 1px solid var(--drf-border); }\n  .drf-refs ol { padding-left: 1.4em; margin: 0; }\n  .drf-refs li { margin-bottom: 0.3em; }\n\n  \/* ── TABLES ── *\/\n  .drf-wrap table { width: 100%; border-collapse: collapse; margin: 1em 0; font-size: 0.92em; }\n  .drf-wrap table th { background: var(--drf-grn-dark); color: #fff; padding: 0.6em 0.8em; text-align: left; font-weight: 500; font-size: 0.85em; letter-spacing: 0.06em; text-transform: uppercase; }\n  .drf-wrap table td { padding: 0.5em 0.8em; border-bottom: 1px solid var(--drf-border); }\n  .drf-wrap table tr:nth-child(even) td { background: #f2f7f3; }\n\u003c\/style\u003e\n\u003cdiv class=\"drf-wrap\"\u003e\n\u003cdiv class=\"drf-tabs-wrap\"\u003e\n\u003cinput type=\"radio\" name=\"drf-ks-tabset\" id=\"drf-ks-tab1\" checked\u003e \u003cinput type=\"radio\" name=\"drf-ks-tabset\" id=\"drf-ks-tab2\"\u003e \u003cinput type=\"radio\" name=\"drf-ks-tabset\" id=\"drf-ks-tab3\"\u003e \u003cinput type=\"radio\" name=\"drf-ks-tabset\" id=\"drf-ks-tab4\"\u003e\n\u003cdiv class=\"drf-tab-labels\"\u003e\n\u003clabel for=\"drf-ks-tab1\"\u003eOverview\u003c\/label\u003e \u003clabel for=\"drf-ks-tab2\"\u003eThe Science\u003c\/label\u003e \u003clabel for=\"drf-ks-tab3\"\u003eHow to Use\u003c\/label\u003e \u003clabel for=\"drf-ks-tab4\"\u003eFAQ\u003c\/label\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-panels\"\u003e\n\u003c!-- ═══════════ TAB 1: OVERVIEW ═══════════ --\u003e\n\u003cdiv class=\"drf-panel\" id=\"drf-ks-panel1\"\u003e\n\u003ch2\u003eKieserite fertiliser — water-soluble magnesium and sulphur for plants\u003c\/h2\u003e\n\u003cdiv class=\"drf-badge-row\"\u003e\n\u003cspan class=\"drf-badge drf-badge-green\"\u003e25% MgO · 50% SO₃\u003c\/span\u003e \u003cspan class=\"drf-badge drf-badge-green\"\u003eFor Plants \u0026amp; Soil\u003c\/span\u003e \u003cspan class=\"drf-badge drf-badge-green\"\u003epH Neutral\u003c\/span\u003e \u003cspan class=\"drf-badge drf-badge-green\"\u003eChloride Free\u003c\/span\u003e \u003cspan class=\"drf-badge drf-badge-gold\"\u003eFully Water-Soluble\u003c\/span\u003e \u003cspan class=\"drf-badge drf-badge-gold\"\u003eSingle Ingredient\u003c\/span\u003e\n\u003c\/div\u003e\n\u003cp\u003e\u003cstrong\u003eKieserite is naturally occurring magnesium sulphate monohydrate (MgSO₄·H₂O), a mined mineral supplying 25% MgO and 50% SO₃ in the sulphate form plant roots absorb directly.\u003c\/strong\u003e It is fully water-soluble at around 393 g per litre, so the magnesium is available to the plant as soon as the granules wet — no waiting on soil acidity, soil bacteria or a pH change to unlock it. That is the difference that matters, because the cheap alternatives are barely soluble at all. Dr Forest supplies it as a single-ingredient granule: one mineral, nothing blended in, nothing added.\u003c\/p\u003e\n\u003cdiv class=\"drf-callout-dark\"\u003e\n\u003cspan class=\"drf-callout-title\"\u003eGarden use only\u003c\/span\u003e\n\u003cp\u003eThis is a garden fertiliser for plants and soil. It is not a human supplement, not a bath salt, and not food grade. Do not ingest. If you want a magnesium supplement or Epsom bathing salts, this is the wrong product.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cp\u003eAgainst Epsom salts the difference is concentration and format, not speed. Both are soluble sulphates and both act fast. Kieserite is the monohydrate at 15% magnesium; Epsom salt is the heptahydrate at 9.8%, so you carry and spread noticeably less product for the same dose. Kieserite comes as a granule you broadcast over soil, where Epsom salt is a fine crystal that suits being dissolved and sprayed. Use Epsom on the leaf, kieserite on the ground.\u003c\/p\u003e\n\u003cdiv class=\"drf-stats\"\u003e\n\u003cdiv class=\"drf-stat\"\u003e\n\u003cspan class=\"drf-stat-number\"\u003e25%\u003c\/span\u003e\u003cspan class=\"drf-stat-label\"\u003eMgO\u003c\/span\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-stat\"\u003e\n\u003cspan class=\"drf-stat-number\"\u003e50%\u003c\/span\u003e\u003cspan class=\"drf-stat-label\"\u003eSO₃\u003c\/span\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-stat\"\u003e\n\u003cspan class=\"drf-stat-number\"\u003e393 g\/L\u003c\/span\u003e\u003cspan class=\"drf-stat-label\"\u003eSolubility\u003c\/span\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-stat\"\u003e\n\u003cspan class=\"drf-stat-number\"\u003e0%\u003c\/span\u003e\u003cspan class=\"drf-stat-label\"\u003eChloride\u003c\/span\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003ch3\u003eWhat gardeners use kieserite for\u003c\/h3\u003e\n\u003cul class=\"drf-uses\"\u003e\n\u003cli\u003e\n\u003cstrong\u003eInterveinal yellowing\u003c\/strong\u003e — yellow between the veins on older, lower leaves while the veins stay green. The signature magnesium deficiency in tomatoes, roses, apples and vines.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTomatoes in growing bags and borders\u003c\/strong\u003e — heavy potash feeding suppresses magnesium uptake. Kieserite restores the balance without adding more potassium.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePotatoes\u003c\/strong\u003e — one of the most magnesium-hungry crops on the allotment, and among the first to show it in the haulm.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eRoses and flowering shrubs\u003c\/strong\u003e — magnesium sits at the centre of every chlorophyll molecule, so leaf colour and flower quality both depend on it.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTop fruit and soft fruit\u003c\/strong\u003e — apples, pears, currants and raspberries on light soils lose magnesium to leaching over winter.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eEricaceous plants\u003c\/strong\u003e — rhododendron, camellia, azalea and blueberry need magnesium but cannot take dolomitic lime, which would push the pH up.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eLawns\u003c\/strong\u003e — magnesium deepens the green without forcing the soft, disease-prone growth a nitrogen-only feed gives you.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSulphur correction\u003c\/strong\u003e — UK soils have received far less atmospheric sulphur since coal burning declined. Brassicas, onions and leeks notice.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOver-limed beds\u003c\/strong\u003e — excess calcium suppresses magnesium uptake. Kieserite corrects it without raising pH further.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNo-dig beds\u003c\/strong\u003e — broadcast over the mulch and water in. No cultivation needed.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eKieserite compared with the alternatives\u003c\/h3\u003e\n\u003cdiv class=\"drf-compare\"\u003e\n\u003cdiv class=\"drf-compare-box\"\u003e\n\u003ch4\u003eKieserite granules — soluble sulphate, soil-applied\u003c\/h4\u003e\n\u003cul\u003e\n\u003cli\u003e15% magnesium, half as much again per kilo as Epsom salt\u003c\/li\u003e\n\u003cli\u003e393 g\/L soluble, so the magnesium is available as soon as it wets\u003c\/li\u003e\n\u003cli\u003eWorks at any soil pH, including ericaceous beds and acid-loving fruit\u003c\/li\u003e\n\u003cli\u003eCarries 20% sulphur alongside the magnesium\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-compare-box\"\u003e\n\u003ch4\u003eEpsom salts — soluble sulphate, foliar-first\u003c\/h4\u003e\n\u003cul\u003e\n\u003cli\u003e9.8% magnesium, so you spread more product for the same dose\u003c\/li\u003e\n\u003cli\u003e710 g\/L soluble — also fast, and better suited to a spray tank\u003c\/li\u003e\n\u003cli\u003eFine crystal rather than a granule, so it spreads less evenly on soil\u003c\/li\u003e\n\u003cli\u003eThe right tool for a foliar correction on a plant already yellowing\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-compare-box\"\u003e\n\u003ch4\u003eMagnesium oxide and dolomitic lime — barely soluble\u003c\/h4\u003e\n\u003cul\u003e\n\u003cli\u003eMagnesium oxide dissolves at 0.006 g\/L, dolomite little better\u003c\/li\u003e\n\u003cli\u003eReleases only as soil acid attacks it, so it stalls at pH 7 and above\u003c\/li\u003e\n\u003cli\u003eDolomite raises pH, ruling it out on blueberries, azaleas and camellias\u003c\/li\u003e\n\u003cli\u003eMonths to respond, and often no response at all on alkaline ground\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-pullquote\"\u003eMagnesium sits at the centre of the chlorophyll molecule. Take it away and the leaf cannot build sugar, however much nitrogen you feed it.\u003c\/div\u003e\n\u003ch3\u003eTypical analysis\u003c\/h3\u003e\n\u003ctable\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003cth\u003eParameter\u003c\/th\u003e\n\u003cth\u003eValue\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMagnesium oxide (MgO)\u003c\/td\u003e\n\u003ctd\u003e25%\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMagnesium (elemental Mg)\u003c\/td\u003e\n\u003ctd\u003e15%\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSulphur trioxide (SO₃)\u003c\/td\u003e\n\u003ctd\u003e50%\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSulphur (elemental S)\u003c\/td\u003e\n\u003ctd\u003e20%\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eChloride\u003c\/td\u003e\n\u003ctd\u003eNil\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSolubility in water\u003c\/td\u003e\n\u003ctd\u003eApprox. 393 g\/L — fully soluble\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003epH in solution\u003c\/td\u003e\n\u003ctd\u003eApprox. 7.0 (neutral)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eForm\u003c\/td\u003e\n\u003ctd\u003eGranular, magnesium sulphate monohydrate MgSO₄·H₂O\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eIngredients\u003c\/td\u003e\n\u003ctd\u003eKieserite. Nothing else.\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003cp\u003eOne ingredient, screened and graded, nothing added. Safe around children, pets and bees once watered in. \u003cem\u003eMade by Growers. Backed by Science.\u003c\/em\u003e\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c!-- ═══════════ TAB 2: THE SCIENCE ═══════════ --\u003e\n\u003cdiv class=\"drf-panel\" id=\"drf-ks-panel2\"\u003e\n\u003ch2\u003eWhy magnesium is the nutrient most UK gardens are quietly short of\u003c\/h2\u003e\n\u003ch3\u003eThe chlorophyll problem\u003c\/h3\u003e\n\u003cp\u003eEvery chlorophyll molecule holds a single magnesium ion at its centre. Between 15 and 35% of the magnesium in a leaf is committed to chlorophyll; the rest activates enzymes and stabilises ribosomes in the cytoplasm (Marschner, 2012). When supply runs short, the plant strips magnesium out of its oldest leaves and moves it to the growing tip. That is why deficiency shows as yellowing between the veins on the \u003cem\u003elower\u003c\/em\u003e leaves first while new growth still looks healthy.\u003c\/p\u003e\n\u003cp\u003eThe damage starts before the yellowing does. Cakmak and Kirkby (2008) showed that magnesium shortage blocks sugar export from the leaf well before any visible symptom appears. Sugars accumulate, photosynthesis backs up, and surplus light energy generates reactive oxygen species that bleach the tissue. A plant can be losing yield for weeks while still looking green.\u003c\/p\u003e\n\u003chr class=\"drf-sep\"\u003e\n\u003ch3\u003eHow magnesium behaves in soil\u003c\/h3\u003e\n\u003cp\u003eMagnesium is a divalent cation held on clay and organic matter, but it binds more weakly than calcium and carries a larger hydration shell, so it sits further from the exchange surface. Gransee and Führs (2013) identify this as the reason magnesium leaches more readily than any other major cation. On sandy or free-draining ground, a wet UK winter strips a meaningful fraction of exchangeable magnesium out of the root zone.\u003c\/p\u003e\n\u003cp\u003eUptake is competitive too. Potassium, calcium and ammonium all compete with magnesium at the root surface, and high concentrations of any of them suppress it (Senbayram et al., 2015). This is the trap most tomato growers fall into: a summer of high-potash liquid feed drives magnesium deficiency in a soil that has plenty of magnesium in it.\u003c\/p\u003e\n\u003ch3\u003eMechanisms of action\u003c\/h3\u003e\n\u003cdiv class=\"drf-mech\"\u003e\n\u003cspan class=\"drf-mech-num\"\u003e01\u003c\/span\u003e\n\u003ch4\u003eChlorophyll assembly\u003c\/h4\u003e\n\u003cp\u003eMagnesium chelatase inserts magnesium into the protoporphyrin ring, the committed step of chlorophyll biosynthesis. Without enough magnesium the pathway stalls and the leaf cannot build the pigment, no matter how much nitrogen is available.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-mech\"\u003e\n\u003cspan class=\"drf-mech-num\"\u003e02\u003c\/span\u003e\n\u003ch4\u003ePhloem loading and sugar export\u003c\/h4\u003e\n\u003cp\u003eSucrose export runs on a proton gradient maintained by magnesium-activated H⁺-ATPase. Cakmak and Kirkby (2008) showed magnesium-deficient plants accumulating carbohydrate in the source leaf while roots and fruit are starved. Roots shrink first, which then worsens uptake of everything else.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-mech\"\u003e\n\u003cspan class=\"drf-mech-num\"\u003e03\u003c\/span\u003e\n\u003ch4\u003eEnzyme activation and ATP\u003c\/h4\u003e\n\u003cp\u003eATP is biologically active as the Mg-ATP complex. Every kinase, every phosphatase, every ATP-spending step of the Calvin cycle needs magnesium as the counter-ion. Tränkner et al. (2018) place magnesium alongside potassium as a co-limiting factor for photosynthetic efficiency for exactly this reason.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-mech\"\u003e\n\u003cspan class=\"drf-mech-num\"\u003e04\u003c\/span\u003e\n\u003ch4\u003ePhotoprotection\u003c\/h4\u003e\n\u003cp\u003eA leaf that cannot export sugar still absorbs light. The surplus energy produces reactive oxygen species, and magnesium-deficient leaves are markedly more prone to photooxidative damage in high light. Greenhouse tomatoes and south-facing rose beds show symptoms first in a bright summer.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-mech\"\u003e\n\u003cspan class=\"drf-mech-num\"\u003e05\u003c\/span\u003e\n\u003ch4\u003eSulphate for protein synthesis\u003c\/h4\u003e\n\u003cp\u003eThe 20% sulphur arrives already as sulphate, the form roots absorb. Sulphur builds cysteine and methionine, and sits at the heart of the glucosinolates that give brassicas and alliums their flavour and pungency. Guo et al. (2016) note that magnesium and sulphur deficiency now frequently occur together in intensively cropped soils.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-mech\"\u003e\n\u003cspan class=\"drf-mech-num\"\u003e06\u003c\/span\u003e\n\u003ch4\u003eSolubility decides everything\u003c\/h4\u003e\n\u003cp\u003eOnly water-soluble magnesium can be absorbed directly by the root. Kieserite dissolves at roughly 393 g\/L; magnesium oxide manages 0.006 g\/L and magnesium carbonate 0.106 g\/L. That is a gap of four to five orders of magnitude, and it is why a bag of magnesium oxide can sit in a neutral soil for a season and do almost nothing.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003chr class=\"drf-sep\"\u003e\n\u003ch3\u003eKieserite against magnesium oxide\u003c\/h3\u003e\n\u003cp\u003eOrlovius and McHoul (2015) compared kieserite with magnesium oxide on potato and sugar beet across multiple sites. Kieserite gave consistently higher leaf magnesium concentrations, because sulphate magnesium is available to the plant straight away while oxide and carbonate forms depend on soil acidity to release them. On neutral or alkaline ground the oxide barely moves at all.\u003c\/p\u003e\n\u003ctable\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003cth\u003eMagnesium source\u003c\/th\u003e\n\u003cth\u003eCompound\u003c\/th\u003e\n\u003cth\u003eSolubility in water\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eEpsom salt\u003c\/td\u003e\n\u003ctd\u003eMgSO₄·7H₂O\u003c\/td\u003e\n\u003ctd\u003e710 g\/L\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e\u003cstrong\u003eKieserite\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd\u003eMgSO₄·H₂O\u003c\/td\u003e\n\u003ctd\u003e\u003cstrong\u003e393 g\/L\u003c\/strong\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMagnesium carbonate\u003c\/td\u003e\n\u003ctd\u003eMgCO₃\u003c\/td\u003e\n\u003ctd\u003e0.106 g\/L\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMagnesium hydroxide\u003c\/td\u003e\n\u003ctd\u003eMg(OH)₂\u003c\/td\u003e\n\u003ctd\u003e0.009 g\/L\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMagnesium oxide\u003c\/td\u003e\n\u003ctd\u003eMgO\u003c\/td\u003e\n\u003ctd\u003e0.006 g\/L\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003cp\u003eBoth sulphates are fast. Everything below them on that table is effectively locked up until the soil is acid enough to dissolve it, which is why a magnesium problem on a chalky or limed garden does not respond to dolomite at all.\u003c\/p\u003e\n\u003ch3\u003eWhere magnesium fits with calcium\u003c\/h3\u003e\n\u003cp\u003eMagnesium and calcium compete, so correcting one without thinking about the other creates the opposite problem. On a heavy soil that needs both, pair kieserite with \u003ca href=\"\/products\/granulated-gypsum-clay-breaker\"\u003egranulated gypsum\u003c\/a\u003e — calcium sulphate supplies calcium and sulphur without shifting pH, which lets you lift both cations while keeping the ratio sane. The historic 5:1 calcium-to-magnesium \"ideal ratio\" from the Albrecht school has not held up: Kopittke and Menzies (2007) reviewed the evidence and found no consistent yield benefit from targeting a fixed ratio. Feed to the deficiency, not to a ratio.\u003c\/p\u003e\n\u003cdiv class=\"drf-refs\"\u003e\n\u003ch4\u003eScientific references\u003c\/h4\u003e\n\u003col\u003e\n\u003cli\u003eCakmak, I. \u0026amp; Kirkby, E.A. (2008). Role of magnesium in carbon partitioning and alleviating photooxidative damage. \u003cem\u003ePhysiologia Plantarum\u003c\/em\u003e, 133(4), 692–704.\u003c\/li\u003e\n\u003cli\u003eGransee, A. \u0026amp; Führs, H. (2013). Magnesium mobility in soils as a challenge for soil and plant analysis, magnesium fertilization and root uptake under adverse growth conditions. \u003cem\u003ePlant and Soil\u003c\/em\u003e, 368, 5–21.\u003c\/li\u003e\n\u003cli\u003eSenbayram, M., Gransee, A., Wahle, V. \u0026amp; Thiel, H. (2015). Role of magnesium fertilisers in agriculture: plant–soil continuum. \u003cem\u003eCrop and Pasture Science\u003c\/em\u003e, 66(12), 1219–1229.\u003c\/li\u003e\n\u003cli\u003eGuo, W., Nazim, H., Liang, Z. \u0026amp; Yang, D. (2016). Magnesium deficiency in plants: an urgent problem. \u003cem\u003eThe Crop Journal\u003c\/em\u003e, 4(2), 83–91.\u003c\/li\u003e\n\u003cli\u003eTränkner, M., Tavakol, E. \u0026amp; Jákli, B. (2018). Functioning of potassium and magnesium in photosynthesis, photosynthate translocation and photoprotection. \u003cem\u003ePhysiologia Plantarum\u003c\/em\u003e, 163(3), 414–431.\u003c\/li\u003e\n\u003cli\u003eHermans, C. \u0026amp; Verbruggen, N. (2005). Physiological characterization of Mg deficiency in \u003cem\u003eArabidopsis thaliana\u003c\/em\u003e. \u003cem\u003eJournal of Experimental Botany\u003c\/em\u003e, 56(418), 2153–2161.\u003c\/li\u003e\n\u003cli\u003eGrzebisz, W. (2013). Crop response to magnesium fertilization as affected by nitrogen supply. \u003cem\u003ePlant and Soil\u003c\/em\u003e, 368, 23–39.\u003c\/li\u003e\n\u003cli\u003eOrlovius, K. \u0026amp; McHoul, J. (2015). Effect of two magnesium fertilizers on leaf magnesium concentration, yield, and quality of potato and sugar beet. \u003cem\u003eJournal of Plant Nutrition\u003c\/em\u003e, 38(13), 2044–2054.\u003c\/li\u003e\n\u003cli\u003eKopittke, P.M. \u0026amp; Menzies, N.W. (2007). A review of the use of the basic cation saturation ratio and the \"ideal\" soil. \u003cem\u003eSoil Science Society of America Journal\u003c\/em\u003e, 71(2), 259–265.\u003c\/li\u003e\n\u003cli\u003eDadebo, M.M., Tan, Q., Wu, S., Sun, X., Li, M., Hashem, I.A. \u0026amp; Hu, C. (2026). Foliar magnesium application enhances fruit external and interior quality and nitrogen use efficiency of tomato under high nitrogen supply. \u003cem\u003eAgronomy\u003c\/em\u003e, 16(13), 1218.\u003c\/li\u003e\n\u003cli\u003eBai, R., Liu, H., Liu, Y. \u0026amp; Yong, J.W.H. (2024). Effects of foliar application of magnesium fertilizer on photosynthesis and growth in grapes. \u003cem\u003eAgronomy\u003c\/em\u003e, 14(11), 2659.\u003c\/li\u003e\n\u003cli\u003eShaddox, T. \u0026amp; Munshaw, G. (2019). \u003cem\u003eMagnesium for Kentucky turfgrasses\u003c\/em\u003e. University of Kentucky Cooperative Extension Service, AGR-243.\u003c\/li\u003e\n\u003cli\u003eMarschner, P. (ed.) (2012). \u003cem\u003eMarschner's Mineral Nutrition of Higher Plants\u003c\/em\u003e, 3rd edition. Academic Press, London.\u003c\/li\u003e\n\u003c\/ol\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c!-- ═══════════ TAB 3: HOW TO USE ═══════════ --\u003e\n\u003cdiv class=\"drf-panel\" id=\"drf-ks-panel3\"\u003e\n\u003ch2\u003eHow to use kieserite — directions for use by crop\u003c\/h2\u003e\n\u003cdiv class=\"drf-callout drf-callout-gold\"\u003e\n\u003cspan class=\"drf-callout-title\"\u003eMeasuring and moisture\u003c\/span\u003e\n\u003cp\u003eA level tablespoon holds roughly 15 g, a level teaspoon about 5 g. Kieserite needs soil moisture to dissolve, so scatter it on damp ground and water it in, or apply just before rain. Broadcast onto bone-dry soil in July it will sit on the surface doing nothing until the weather breaks.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-callout-dark\"\u003e\n\u003cspan class=\"drf-callout-title\"\u003eMore is not better\u003c\/span\u003e\n\u003cp\u003eMagnesium competes with calcium and potassium at the root. Overloading a soil with magnesium suppresses calcium uptake, which brings blossom end rot in tomatoes and bitter pit in apples, and it degrades the crumb structure of clay soils. \u003cstrong\u003eDo not exceed 30 g per square metre in a season\u003c\/strong\u003e, and skip the application entirely if a soil test shows a Magnesium Index of 3 or above. If leaves are yellow but the veins are yellow too, the problem is nitrogen or iron, not magnesium.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003ch3\u003eApplication rates by crop\u003c\/h3\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eTomatoes, peppers and aubergines\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 20 g\/m² before planting  |  \u003cstrong\u003eTop-up:\u003c\/strong\u003e 10 g\/m² at first truss\u003c\/div\u003e\n\u003cp\u003eThe classic case. A summer of high-potash tomato feed suppresses magnesium uptake and the lower leaves yellow between the veins by midsummer. Work 20 g\/m² into border soil before planting, then scatter a second 10 g\/m² and water it in as the first truss sets. In pots and growing bags, mix 3–5 g per 10 litres of compost before planting.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003ePotatoes\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 25–30 g\/m²  |  \u003cstrong\u003eTiming:\u003c\/strong\u003e In the trench at planting\u003c\/div\u003e\n\u003cp\u003ePotatoes remove more magnesium than almost anything else on the plot, and the haulm shows it early: interveinal yellowing on lower leaves spreading upward as tubers bulk. Scatter along the trench and cover. Use the upper end of the range on light sandy soils.\u003c\/p\u003e\n\u003cspan class=\"drf-rate-cite\"\u003eRate scaled from field trials on potato and sugar beet, Orlovius \u0026amp; McHoul (2015), J. Plant Nutrition 38(13): 2044–2054.\u003c\/span\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eRoses and flowering shrubs\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 20 g\/m² in spring  |  \u003cstrong\u003eSecond dose:\u003c\/strong\u003e 15 g\/m² after the first flush\u003c\/div\u003e\n\u003cp\u003eApply in March as growth breaks, spread across the root zone rather than at the stem, and water in. A second dose after the first flush carries colour through the later blooms. Roses on chalk or heavily limed beds respond particularly well, because the excess calcium has been suppressing magnesium uptake.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eApples, pears and top fruit\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 25 g\/m²  |  \u003cstrong\u003eTiming:\u003c\/strong\u003e Late winter to early spring, annually\u003c\/div\u003e\n\u003cp\u003eSpread evenly under the canopy out to the drip line, never in a ring at the trunk. Magnesium deficiency in apples shows as interveinal yellowing followed by early leaf drop from the base of the shoot, and it is worse in a heavy cropping year. Repeat annually on sandy orchard soils.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eStrawberries, raspberries and currants\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 15–20 g\/m²  |  \u003cstrong\u003eTiming:\u003c\/strong\u003e Early spring, before flowering\u003c\/div\u003e\n\u003cp\u003eSoft fruit on light soil loses magnesium over winter. Apply along the row in March and water in. For strawberries, apply after cutting back old foliage rather than during fruiting. Blackcurrants are especially prone and benefit from the sulphur as well.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eBrassicas, onions and leeks\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 15 g\/m²  |  \u003cstrong\u003eTiming:\u003c\/strong\u003e Worked in before planting out\u003c\/div\u003e\n\u003cp\u003eThis group is fed as much for the sulphur as the magnesium. Sulphur builds the compounds responsible for flavour and pungency in cabbage, sprouts, onions and leeks. Rake into the top 10 cm of the bed a week or two before transplanting.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eGrapes and vines\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 20–25 g\/m²  |  \u003cstrong\u003eTiming:\u003c\/strong\u003e Early spring, before bud break\u003c\/div\u003e\n\u003cp\u003eMagnesium deficiency in vines is common and unmistakable: yellowing between the veins on basal leaves, often with a reddish margin on dark varieties, worsening as bunches fill. Apply around the base out to the spread of the canopy and water in well.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eRhododendron, camellia, azalea and blueberry\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 15 g\/m²  |  \u003cstrong\u003eTiming:\u003c\/strong\u003e Spring, once a year\u003c\/div\u003e\n\u003cp\u003eThese plants need magnesium but cannot tolerate the pH lift from dolomitic lime, which makes kieserite the sensible route for ericaceous beds. Scatter over the mulch, water in, and top the mulch back up.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eLawns — dry granules\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 15–20 g\/m²  |  \u003cstrong\u003eTiming:\u003c\/strong\u003e Spring or early autumn\u003c\/div\u003e\n\u003cp\u003eMagnesium deepens turf colour without forcing the lush, soft growth a straight nitrogen feed produces. Apply to damp grass on a still day, \u003cem\u003ewater in properly\u003c\/em\u003e, and leave the mower for two or three days. Granules left sitting dry on turf in sun can mark the leaf. Useful on sandy lawns that have been sanded and top-dressed repeatedly, where magnesium leaches out fastest. Turf research puts the useful range at 0.5–1 lb magnesium per 1,000 sq ft, which works out at 16–32 g\/m² of kieserite; stay at the lower end unless a soil test has confirmed a shortage, and never exceed 30 g\/m² in a season.\u003c\/p\u003e\n\u003cspan class=\"drf-rate-cite\"\u003eShaddox \u0026amp; Munshaw (2019), Magnesium for Kentucky turfgrasses, University of Kentucky Cooperative Extension AGR-243.\u003c\/span\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eLawns — liquid feed\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eLight top-up:\u003c\/strong\u003e 3 g\/L at 1 L\/m², every 3–4 weeks  |  \u003cstrong\u003eFull correction:\u003c\/strong\u003e 3–4 g\/L at 5 L\/m², once in spring\u003c\/div\u003e\n\u003cp\u003eLiquid suits turf better than most things, because you cannot rake granules into an established lawn and anything left on the surface has to wait for rain. Dissolve, strain, and apply through a watering can with a fine rose or a hose-end feeder, then water the lawn afterwards to move it off the leaf and into the root zone.\u003c\/p\u003e\n\u003cp\u003eThe light top-up delivers about 3 g\/m² a pass and matches the foliar rate in the turf literature. Published turf foliar guidance is written for low-volume professional sprayers and works out near 79 g\/L, which will scorch a domestic lawn applied through a can — the rates here deliver the same magnesium per square metre at a concentration turf tolerates. Do not go above 13 g\/L on grass.\u003c\/p\u003e\n\u003cspan class=\"drf-rate-cite\"\u003eConverted from Shaddox \u0026amp; Munshaw (2019), AGR-243 — foliar 0.1 lb Mg per 1,000 sq ft.\u003c\/span\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-callout-dark\"\u003e\n\u003cspan class=\"drf-callout-title\"\u003eMagnesium is not the lawn greener you may be thinking of\u003c\/span\u003e\n\u003cp\u003eThe product that turns a lawn dark green within days and blackens moss is \u003cstrong\u003eiron sulphate\u003c\/strong\u003e, not magnesium sulphate. They are different minerals doing different jobs, and they are constantly confused. Magnesium builds chlorophyll over three to six weeks and does nothing to moss. If your lawn is pale because it is short of magnesium — older leaves yellowing between the veins, worst on sand, worst after a hard winter — kieserite is the right answer. If you want an instant colour hit or you are fighting moss, buy iron and leave this on the shelf.\u003c\/p\u003e\n\u003cp\u003eWorth testing before you treat. Turf guidance says apply magnesium when a soil test reads at or below 20 ppm; in UK terms that is Magnesium Index 0 or 1. Lawns that have been limed recently, or fed heavily on autumn potash, are the likeliest to be genuinely short, because calcium and potassium both displace magnesium from the soil's exchange sites.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eConifers and evergreen hedging\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 20–25 g\/m²  |  \u003cstrong\u003eTiming:\u003c\/strong\u003e Early spring\u003c\/div\u003e\n\u003cp\u003eBronzing and yellowing of older needles on the inside of the plant is a classic magnesium picture in conifer hedging, particularly on hedges that have never been fed. Apply along both sides of the hedge line out to the spread of the branches.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eGeneral soil correction — beds, borders and no-dig plots\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 15–25 g\/m²  |  \u003cstrong\u003eFrequency:\u003c\/strong\u003e Once a year, spring\u003c\/div\u003e\n\u003cp\u003eAt Magnesium Index 0 or 1, use 25 g\/m². At Index 2, use 15 g\/m² as maintenance. At Index 3 or above, do not apply. On sandy soils an annual application is normal; on heavy clay every second or third year is usually enough. For no-dig beds, broadcast over the mulch and water in — no cultivation needed.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003chr class=\"drf-sep\"\u003e\n\u003ch3\u003eUsing kieserite as a liquid feed\u003c\/h3\u003e\n\u003cp\u003eThe granules are made for broadcasting, but the mineral itself is fully soluble, so you can dissolve it and water it on or spray it. Two things to understand before you do.\u003c\/p\u003e\n\u003cp\u003eFirst, dissolving takes time. A 2–5mm granule in cold, still water needs \u003cstrong\u003etwo to four hours\u003c\/strong\u003e to go into solution. That is granule size and surface area, not low solubility — kieserite saturates at around 393 g per litre, and the 13 g\/L foliar rate below is barely 3% of that. Warm water and a stir at the start and end cut the time considerably.\u003c\/p\u003e\n\u003cp\u003eSecond, this is mined rock rather than a refined laboratory salt, so a little insoluble grit is normal. Let the solution stand, then decant the clear liquid or strain it through muslin before it goes anywhere near a sprayer.\u003c\/p\u003e\n\u003cdiv class=\"drf-callout-dark\"\u003e\n\u003cspan class=\"drf-callout-title\"\u003eNever tank-mix with a calcium feed\u003c\/span\u003e\n\u003cp\u003eMagnesium sulphate solution plus any soluble calcium — gypsum, calcium nitrate, an amino-chelated calcium — precipitates calcium sulphate on the spot. Calcium sulphate dissolves at roughly 2.4 g per litre against kieserite's 393, so it drops out as a white sludge that blocks nozzles and takes both nutrients out of solution with it. \u003cstrong\u003eMix and apply them separately.\u003c\/strong\u003e Applied to soil on different days they work together perfectly well; in the same tank they cancel each other out.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003ch4\u003eHow to make it up\u003c\/h4\u003e\n\u003col class=\"drf-steps\"\u003e\n\u003cli\u003e\n\u003cstrong\u003eWeigh into a bucket.\u003c\/strong\u003e Work out the total volume you need first, then the weight from the rate cards below. A level tablespoon is roughly 15 g.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eStart with warm water.\u003c\/strong\u003e Add about a third of the final volume, hand-warm rather than hot, and stir hard for a minute.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eLeave it two to four hours.\u003c\/strong\u003e Cover it and walk away. Stir again when you come back — the last of the granules go quickly once the water is saturated near the bottom.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTop up to volume and settle.\u003c\/strong\u003e Add the remaining cold water, then leave it twenty minutes for any grit to drop out.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDecant or strain.\u003c\/strong\u003e Pour off the clear liquid, or strain through muslin. Essential for a sprayer, optional for a watering can. Use it within a day or two.\u003c\/li\u003e\n\u003c\/ol\u003e\n\u003ch4\u003eWorking out the rate\u003c\/h4\u003e\n\u003cp\u003eMost published magnesium spray guidance is written for Epsom salt. Kieserite carries about half as much magnesium again per gram, so use roughly two-thirds the Epsom weight for the same dose.\u003c\/p\u003e\n\u003ctable\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003cth\u003ePublished Epsom rate\u003c\/th\u003e\n\u003cth\u003eEpsom\u003c\/th\u003e\n\u003cth\u003eMagnesium delivered\u003c\/th\u003e\n\u003cth\u003eKieserite equivalent\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e0.5% solution\u003c\/td\u003e\n\u003ctd\u003e5 g\/L\u003c\/td\u003e\n\u003ctd\u003e0.49 g Mg\/L\u003c\/td\u003e\n\u003ctd\u003e3 g\/L\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e1% solution\u003c\/td\u003e\n\u003ctd\u003e10 g\/L\u003c\/td\u003e\n\u003ctd\u003e0.99 g Mg\/L\u003c\/td\u003e\n\u003ctd\u003e6.5 g\/L\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e\n\u003cstrong\u003e2% solution\u003c\/strong\u003e (standard horticultural foliar)\u003c\/td\u003e\n\u003ctd\u003e20 g\/L\u003c\/td\u003e\n\u003ctd\u003e1.97 g Mg\/L\u003c\/td\u003e\n\u003ctd\u003e\u003cstrong\u003e13 g\/L\u003c\/strong\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e5% solution (field-scale, not for gardens)\u003c\/td\u003e\n\u003ctd\u003e50 g\/L\u003c\/td\u003e\n\u003ctd\u003e4.93 g Mg\/L\u003c\/td\u003e\n\u003ctd\u003e33 g\/L\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eFoliar spray — general correction\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 6.5 g\/L to start, 13 g\/L maximum  |  \u003cstrong\u003eFrequency:\u003c\/strong\u003e Every 2–3 weeks, up to three sprays\u003c\/div\u003e\n\u003cp\u003eTwo per cent Epsom solution is the long-standing horticultural foliar rate, and 13 g\/L of kieserite matches it. Start at 6.5 g\/L on anything you have not sprayed before and test a few leaves first. Spray early morning or evening, never in strong sun, and wet the undersides as well as the tops — most magnesium goes in through the lower leaf surface.\u003c\/p\u003e\n\u003cspan class=\"drf-rate-cite\"\u003e2% w\/v magnesium sulphate, three applications: Dadebo et al. (2026), Agronomy 16(13): 1218.\u003c\/span\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eFoliar spray — tomatoes and peppers\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 13 g\/L  |  \u003cstrong\u003eFrequency:\u003c\/strong\u003e Three sprays through the growing period\u003c\/div\u003e\n\u003cp\u003eThe tomato trial behind this rate applied 2% magnesium sulphate three times during vegetative growth and recorded gains in fruit yield, vitamin C, titratable acidity and colour alongside better nitrogen use. Useful as a rescue on plants already yellowing between the veins, where the soil correction will take too long to save the current crop.\u003c\/p\u003e\n\u003cspan class=\"drf-rate-cite\"\u003eDadebo et al. (2026), Agronomy 16(13): 1218.\u003c\/span\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eFoliar spray — apples, pears and top fruit\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 13 g\/L  |  \u003cstrong\u003eFrequency:\u003c\/strong\u003e From petal fall, repeat 2–3 times at 2–3 week intervals\u003c\/div\u003e\n\u003cp\u003eTree fruit guidance puts Epsom at 2 kg per 100 litres, which is the same 2% solution. Start once the leaves are properly developed or at petal fall, and repeat where symptoms are already showing. Soil correction still does the long-term work; the spray buys you this season's crop.\u003c\/p\u003e\n\u003cspan class=\"drf-rate-cite\"\u003eBC Tree Fruit Production Guide, magnesium section — 2 kg magnesium sulphate per 100 L.\u003c\/span\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eFoliar spray — grapes and vines\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 0.3–0.5 g\/L  |  \u003cstrong\u003eFrequency:\u003c\/strong\u003e Up to four times during fruit fill\u003c\/div\u003e\n\u003cp\u003eGo far lighter here than anywhere else. The vine trial that measured this found the response peaked at 2.14 mM and fell away above it — the equivalent of about 0.35 g of kieserite per litre. Spraying vines at the tomato rate during fruit fill overshoots the optimum rather than improving on it. Late afternoon on a dry day.\u003c\/p\u003e\n\u003cspan class=\"drf-rate-cite\"\u003eBai, Liu, Liu \u0026amp; Yong (2024), Agronomy 14(11): 2659 — optimum 2.14 mM MgSO₄·7H₂O.\u003c\/span\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eSoil drench — beds and borders\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 3–5 g\/L applied at 5 L\/m²  |  \u003cstrong\u003eFrequency:\u003c\/strong\u003e Once, in spring\u003c\/div\u003e\n\u003cp\u003eThis is the dry soil rate delivered in water rather than a different dose. Four grams per litre over five litres per square metre puts down 20 g\/m², exactly the general bed rate. Use it where you want the magnesium down at root depth immediately, or on a no-dig bed where you would rather not have granules sitting on the mulch. The seasonal ceiling of 30 g\/m² is the same whichever way you apply it.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-rate\"\u003e\n\u003ch4\u003eSoil drench — pots, containers and growing bags\u003c\/h4\u003e\n\u003cdiv class=\"drf-rate-meta\"\u003e\n\u003cstrong\u003eRate:\u003c\/strong\u003e 1–2 g\/L  |  \u003cstrong\u003eFrequency:\u003c\/strong\u003e Monthly through the growing season\u003c\/div\u003e\n\u003cp\u003eWater it on in place of one normal watering, enough to wet the whole rootball and just start to run from the base. One gram per litre monthly through a season lands close to the 3–5 g per 10 litres you would have mixed into the compost at potting. Skip it if the feed you are already using declares magnesium.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-callout drf-callout-gold\"\u003e\n\u003cspan class=\"drf-callout-title\"\u003eDissolving does not change the total\u003c\/span\u003e\n\u003cp\u003eA litre of solution is a delivery method, not an extra dose. Whatever goes on as liquid counts towards the same 30 g per square metre seasonal ceiling as the dry granules, and the same rule applies about not applying at all above Magnesium Index 3. Foliar sprays are the one exception worth noting — they bypass the soil entirely, so they correct the plant without loading the ground, which is exactly why they suit a mid-season rescue.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003chr class=\"drf-sep\"\u003e\n\u003ch3\u003eStep-by-step application\u003c\/h3\u003e\n\u003col class=\"drf-steps\"\u003e\n\u003cli\u003e\n\u003cstrong\u003eCheck the symptom first.\u003c\/strong\u003e Magnesium deficiency yellows the tissue \u003cem\u003ebetween\u003c\/em\u003e the veins while the veins stay green, and it starts on the oldest leaves. If the whole leaf is pale, or new growth is affected first, look at nitrogen or iron instead. Our guide to \u003ca href=\"\/blogs\/the-dr-forest-blog\/why-are-my-tomato-leaves-turning-yellow\"\u003eyellow leaves on tomato plants\u003c\/a\u003e walks through the patterns.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWeigh it rather than guessing.\u003c\/strong\u003e Twenty grams per square metre is roughly a heaped tablespoon — far less than most people scatter by eye.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSpread evenly on moist soil.\u003c\/strong\u003e Broadcast across the whole root zone. Never pile it against stems or trunks.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWater it in.\u003c\/strong\u003e Five to ten litres per square metre, or apply just before forecast rain. This is what starts the dissolution.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eReassess on the new growth.\u003c\/strong\u003e Leaves already damaged will not re-green, because magnesium moves out of them and does not come back. Judge the result on leaves that emerge afterwards, three to six weeks on.\u003c\/li\u003e\n\u003c\/ol\u003e\n\u003ch3\u003eFive common mistakes\u003c\/h3\u003e\n\u003cul class=\"drf-uses\"\u003e\n\u003cli\u003e\n\u003cstrong\u003eApplying it dry and walking away\u003c\/strong\u003e — without water the granules do nothing.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eExpecting old leaves to recover\u003c\/strong\u003e — they will not. The plant has already withdrawn their magnesium.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTipping dry granules into a sprayer\u003c\/strong\u003e — they need two to four hours in water first, and straining afterwards. Dissolve properly and the solution sprays fine; skip that step and you block the nozzle. See the liquid feed section above, and our take on when a magnesium spray helps in \u003ca href=\"\/blogs\/the-dr-forest-blog\/epsom-salt-for-roses-does-it-actually-work-2\"\u003eEpsom salt for roses: does it actually work?\u003c\/a\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMixing it with a calcium feed in one tank\u003c\/strong\u003e — you get calcium sulphate sludge and lose both nutrients.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAdding magnesium to an already magnesium-rich clay\u003c\/strong\u003e — many UK clays are. Test before correcting.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAssuming any yellow leaf means magnesium\u003c\/strong\u003e — overwatering, nitrogen shortage and iron chlorosis each yellow foliage in a different pattern.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cdiv class=\"drf-callout\"\u003e\n\u003cspan class=\"drf-callout-title\"\u003eWorks well combined with…\u003c\/span\u003e\n\u003cp\u003e\u003ca href=\"\/products\/granulated-gypsum-clay-breaker\"\u003e\u003cstrong\u003eGranulated Gypsum\u003c\/strong\u003e\u003c\/a\u003e is the natural partner. Kieserite supplies magnesium and sulphur; gypsum supplies calcium and sulphur. Because magnesium and calcium compete at the root, lifting one without the other tends to create the deficiency you have just corrected in reverse. Both are pH neutral and both are granular, so they spread together and suit the same beds — particularly heavy clay, where the gypsum also improves structure. Apply them in the same pass as dry granules, at their own rates, and water in together. What you must not do is dissolve the two into one watering can: sulphate plus calcium precipitates calcium sulphate and you lose both.\u003c\/p\u003e\n\u003cp\u003eAvoid stacking kieserite with dolomitic lime in the same year. Both supply magnesium and you will overshoot.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-callout drf-callout-gold\"\u003e\n\u003cspan class=\"drf-callout-title\"\u003eStorage and handling\u003c\/span\u003e\n\u003cp\u003eKeep the bag closed in a dry place, off a concrete floor. Kieserite draws moisture from the air, so an open bag in a damp shed will cake into a block — break it up with a trowel and use it as normal, the analysis is unchanged. Wear gloves if you have sensitive skin, wash hands afterwards, and store out of reach of children and pets as you would any garden fertiliser.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c!-- ═══════════ TAB 4: FAQ ═══════════ --\u003e\n\u003cdiv class=\"drf-panel\" id=\"drf-ks-panel4\"\u003e\n\u003ch2\u003eKieserite questions, answered\u003c\/h2\u003e\n\u003cdiv class=\"drf-faq\"\u003e\n\u003cinput type=\"checkbox\" id=\"drf-ks-faq1\"\u003e\u003clabel class=\"drf-faq-q\" for=\"drf-ks-faq1\"\u003eCan I take this as a magnesium supplement, or use it in the bath?\u003c\/label\u003e\n\u003cdiv class=\"drf-faq-a\"\u003e\n\u003cdiv\u003eNo. This is a garden fertiliser for plants and soil. It is not food grade, it has not been tested to the heavy-metal limits that apply to supplements or cosmetics, and it is not intended for human or animal consumption or for bathing. If you want magnesium for yourself, buy a product sold for that purpose from a pharmacy. Everything on this page is about feeding plants.\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-faq\"\u003e\n\u003cinput type=\"checkbox\" id=\"drf-ks-faq2\"\u003e\u003clabel class=\"drf-faq-q\" for=\"drf-ks-faq2\"\u003eWhat is kieserite and what does it do?\u003c\/label\u003e\n\u003cdiv class=\"drf-faq-a\"\u003e\n\u003cdiv\u003eKieserite is the mineral form of magnesium sulphate monohydrate, MgSO₄·H₂O. It is mined, dried and graded rather than chemically manufactured. As a garden fertiliser it supplies 25% MgO (15% magnesium) and 50% SO₃ (20% sulphur), both as sulphate, which is the form plant roots take up directly. Magnesium sits at the centre of the chlorophyll molecule; sulphur builds the amino acids cysteine and methionine.\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-faq\"\u003e\n\u003cinput type=\"checkbox\" id=\"drf-ks-faq3\"\u003e\u003clabel class=\"drf-faq-q\" for=\"drf-ks-faq3\"\u003eWhat is the difference between kieserite and Epsom salts?\u003c\/label\u003e\n\u003cdiv class=\"drf-faq-a\"\u003e\n\u003cdiv\u003eWater of crystallisation, which changes the concentration and the format rather than the speed. Epsom salt is magnesium sulphate heptahydrate — seven water molecules, 9.8% magnesium, 710 g\/L soluble. Kieserite is the monohydrate — one water molecule, 15% magnesium, 393 g\/L soluble. Both are fully soluble sulphates and both act quickly. The practical split is format. Kieserite comes as a granule for broadcasting over soil and gives you half as much magnesium again per kilo; Epsom salt is a fine crystal that dissolves in seconds. If you want to spray kieserite you can, but it needs two to four hours in water and a strain first — see the liquid feed section under How to Use, which includes the conversion table for turning any published Epsom rate into a kieserite one.\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-faq\"\u003e\n\u003cinput type=\"checkbox\" id=\"drf-ks-faq4\"\u003e\u003clabel class=\"drf-faq-q\" for=\"drf-ks-faq4\"\u003eHow much magnesium fertiliser do I need per square metre?\u003c\/label\u003e\n\u003cdiv class=\"drf-faq-a\"\u003e\n\u003cdiv\u003eFor most garden plants, 15–25 g\/m² once a year in spring. Potatoes and top fruit take the upper end at 25–30 g\/m². Leafy vegetables and ericaceous shrubs need less, around 15 g\/m². A level tablespoon is roughly 15 g. Do not exceed 30 g\/m² in a season.\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-faq\"\u003e\n\u003cinput type=\"checkbox\" id=\"drf-ks-faq5\"\u003e\u003clabel class=\"drf-faq-q\" for=\"drf-ks-faq5\"\u003eHow do I know my plants actually need magnesium?\u003c\/label\u003e\n\u003cdiv class=\"drf-faq-a\"\u003e\n\u003cdiv\u003eLook at the pattern, not the colour alone. Magnesium deficiency yellows the tissue between the veins while the veins themselves stay green, and it always starts on the older, lower leaves because the plant moves magnesium up to new growth. A uniformly pale leaf points to nitrogen. Yellow new leaves with green veins point to iron. A soil test giving a Magnesium Index settles it properly.\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-faq\"\u003e\n\u003cinput type=\"checkbox\" id=\"drf-ks-faq6\"\u003e\u003clabel class=\"drf-faq-q\" for=\"drf-ks-faq6\"\u003eWill kieserite change my soil pH?\u003c\/label\u003e\n\u003cdiv class=\"drf-faq-a\"\u003e\n\u003cdiv\u003eNo. Magnesium sulphate is pH neutral in solution, which is the main reason to choose it over dolomitic lime. Dolomite supplies magnesium but raises pH, so it is unusable on blueberries, rhododendrons, azaleas and camellias, and it does little on soils already at pH 7 or above. Kieserite works at any pH.\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-faq\"\u003e\n\u003cinput type=\"checkbox\" id=\"drf-ks-faq7\"\u003e\u003clabel class=\"drf-faq-q\" for=\"drf-ks-faq7\"\u003eCan I apply too much?\u003c\/label\u003e\n\u003cdiv class=\"drf-faq-a\"\u003e\n\u003cdiv\u003eYes, and it matters. Magnesium competes with calcium and potassium for uptake at the root. Push magnesium too high and you suppress calcium, which brings \u003ca href=\"\/blogs\/the-dr-forest-blog\/blossom-end-rot-tomatoes\"\u003eblossom end rot in tomatoes\u003c\/a\u003e and bitter pit in apples. On clay soils, excess magnesium also degrades crumb structure and makes the ground harder to work. Stay within 30 g\/m² per season and skip it entirely if a soil test shows Magnesium Index 3 or above.\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-faq\"\u003e\n\u003cinput type=\"checkbox\" id=\"drf-ks-faq8\"\u003e\u003clabel class=\"drf-faq-q\" for=\"drf-ks-faq8\"\u003eHow quickly will I see results?\u003c\/label\u003e\n\u003cdiv class=\"drf-faq-a\"\u003e\n\u003cdiv\u003eThree to six weeks in the new growth, provided the soil stays moist. Judge it on leaves that emerge after the application. Leaves already yellow will not re-green, because the plant has withdrawn their magnesium and redistributed it — that damage is permanent on those leaves.\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-faq\"\u003e\n\u003cinput type=\"checkbox\" id=\"drf-ks-faq9\"\u003e\u003clabel class=\"drf-faq-q\" for=\"drf-ks-faq9\"\u003eIs it organic, and is it safe for children, pets and bees?\u003c\/label\u003e\n\u003cdiv class=\"drf-faq-a\"\u003e\n\u003cdiv\u003eKieserite is a mined mineral, screened and graded, with nothing added. It is a mineral rather than a certified organic input, so we do not describe it as certified organic. It has no pesticide action, so it poses no risk to bees or other pollinators. Water it into the soil after applying and keep children and pets off the treated area until you have.\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-faq\"\u003e\n\u003cinput type=\"checkbox\" id=\"drf-ks-faq10\"\u003e\u003clabel class=\"drf-faq-q\" for=\"drf-ks-faq10\"\u003eCan I mix it with other Dr Forest products?\u003c\/label\u003e\n\u003cdiv class=\"drf-faq-a\"\u003e\n\u003cdiv\u003eYes. It pairs particularly well with \u003ca href=\"\/products\/granulated-gypsum-clay-breaker\"\u003eGranulated Gypsum\u003c\/a\u003e — kieserite brings magnesium and sulphur, gypsum brings calcium and sulphur, and because the two cations compete at the root it makes sense to lift them together rather than one at a time. Both are pH neutral and both are granular, so they spread in the same pass. It also sits happily alongside granular fertilisers. Two things to avoid: applying it in the same season as dolomitic lime, since both supply magnesium; and dissolving it into the same tank as any calcium feed, which precipitates calcium sulphate and takes both nutrients out of solution. As dry granules on soil they pair perfectly — it is only in the watering can that they clash.\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"drf-faq\"\u003e\n\u003cinput type=\"checkbox\" id=\"drf-ks-faq11\"\u003e\u003clabel class=\"drf-faq-q\" for=\"drf-ks-faq11\"\u003eCan I dissolve kieserite in water and use it as a liquid feed?\u003c\/label\u003e\n\u003cdiv class=\"drf-faq-a\"\u003e\n\u003cdiv\u003eYes. It is fully soluble at around 393 g\/L, so a foliar spray or a soil drench both work. The catch is time: a 2–5mm granule needs two to four hours in water, ideally started warm and stirred at both ends. Because this is mined rock rather than a refined salt, let the solution settle and decant or strain it before it goes in a sprayer. As a rule of thumb, kieserite carries about half as much magnesium again per gram as Epsom salt, so use roughly two-thirds the weight of any published Epsom rate — the standard 2% foliar solution works out at 13 g of kieserite per litre. Full rates by crop, and the conversion table, are in the How to Use tab.\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e","brand":"Dr Forest","offers":[{"title":"1.5kg","offer_id":58378071212406,"sku":"DF-KIES-1.5","price":10.49,"currency_code":"GBP","in_stock":true},{"title":"4kg","offer_id":58378071245174,"sku":"DF-KIES-4","price":19.35,"currency_code":"GBP","in_stock":true},{"title":"9kg","offer_id":58378071277942,"sku":"DF-KIES-9","price":30.99,"currency_code":"GBP","in_stock":true},{"title":"15kg","offer_id":58378071310710,"sku":"DF-KIES-15","price":44.49,"currency_code":"GBP","in_stock":true},{"title":"30kg","offer_id":58378071343478,"sku":"DF-KIES-30","price":89.99,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0049\/8194\/8504\/files\/keiseritemineralupclose.jpg?v=1785577099","url":"https:\/\/www.drforest.co.uk\/products\/kieserite-magnesium-sulphate-fertiliser","provider":"Dr Forest","version":"1.0","type":"link"}