Fertiliser
Tomato Feed 3-4-6 | Slow-Release, Made with Organic Ingredients
A slow-release 3-4-6 feed for tomatoes.
from £11.50
How Potato Fertiliser compares
Full guide and scienceDr Forest Potato Fertiliser 3-5-8 — slow-release powder
- 20 ingredients, with 7% calcium, 2.4% magnesium and trace minerals
- Mineral potash from sulphate of potash and polyhalite, no muriate
- Applied at planting and earthing up, then every 3–4 weeks through bulking
- Plant meals and seaweed add organic matter as they break down; the biochar lasts
Typical liquid potato feed — diluted concentrate
- NPK, often with little or no calcium or magnesium on the label
- Potash source varies, so check the label for potassium chloride
- Usually mixed and watered on every week or two
- Feeds the plant but adds little or nothing to the soil
Customer highlight
Iv used dr forest potato fertilizer on multiple varieties of normal potato and sweet potatos iv noticed the foliage has explored the stems are nice and thick aswell another great product from Dr forest great service and great knowledge about what fertilizers you need get some before its gone
Editorial highlight from marketplace and store reviews — separate from the full review list below.
Made by Growers · Backed by Science
Organic potato fertiliser 3-5-8 — 20 ingredients, potash-led for starch and flavour
3-5-8 NPK 20 Ingredients Sulphate-Form Potash Slow Release Full Ingredient Transparency Handcrafted in Stockport
Dr Forest Potato Fertiliser is a 3-5-8 organic potato fertiliser: a slow-release, high-potash powder for earlies and maincrops in beds, grow bags and pots. Potassium helps the tuber turn sugar into starch, so the formula leans on K and keeps nitrogen moderate. It is blended in small batches in Stockport from 20 ingredients, each one listed on the Ingredients tab.
The main potash sources are sulphate of potash and Yorkshire polyhalite, with no muriate of potash (potassium chloride), which trials link to lower starch. Alongside it sit 7% calcium, 2.4% magnesium, plant meals, Scottish seaweed, British biochar and a living microbial culture. It goes in at planting and at earthing up, then every 3–4 weeks while the tubers bulk.
3-5-8NPK ratio
7%Calcium
2.4%Magnesium
2.7:1K : N ratio
What this formula does for your potatoes
- Starch and dry matter — 8% potash, mostly in sulphate form. Potassium switches on starch synthase, the enzyme that builds starch.
- Tuber set — 5% phosphate, mainly from a quick source and a slow one, for the weeks when tubers are forming.
- Leaf kept in proportion — 3% nitrogen, mostly from plant proteins and meals, so the plant doesn't run to haulm.
- Calcium in the ridge — 7% calcium, mainly from four ingredients, in the soil right around the tubers, where they take it up.
- Sugar to the tubers — 2.4% magnesium, mainly from three sources; without enough, sugar stays stuck in the leaves.
- Soil that keeps working — seaweed, biochar, clay minerals, humic acid and a microbial culture add what a soluble feed doesn't.
Dr Forest potato fertiliser vs a liquid potato feed
Dr Forest Potato Fertiliser 3-5-8 — slow-release powder
- 20 ingredients, with 7% calcium, 2.4% magnesium and trace minerals
- Mineral potash from sulphate of potash and polyhalite, no muriate
- Applied at planting and earthing up, then every 3–4 weeks through bulking
- Plant meals and seaweed add organic matter as they break down; the biochar lasts
Typical liquid potato feed — diluted concentrate
- NPK, often with little or no calcium or magnesium on the label
- Potash source varies, so check the label for potassium chloride
- Usually mixed and watered on every week or two
- Feeds the plant but adds little or nothing to the soil
Handcrafted in Stockport
Dr Forest was founded in 2020 in Stockport, Greater Manchester, and is named after Joe's grandfather, Dr Forrest, a GP in a Lancashire mining town near Preston who kept a back-garden plot for the runner beans he turned into piccalilli for family and friends. This premium organic plant food comes in compostable kraft packs. More on the potash in polyhalite vs sulphate of potash. Made by Growers. Backed by Science.
What's Inside
All 20 ingredients — what each one does for potatoes
Twenty ingredients, each with a job. The polyhalite is mined in North Yorkshire, the seaweed meal hand-harvested in Scotland, and the biochar, rapeseed meal and clay minerals are British. Each card shows how quickly it releases.
01Steady release
Nitrogen plant extract — plant protein concentrate
The main nitrogen carrier, at 12% N. Soil microbes break the protein down over the weeks after planting, so nitrogen arrives steadily. A surge while tubers are forming pushes growth into the haulm.
02Fast–moderate release
Phosphorous meal — calcined plant meal
A heat-processed plant meal with about 15% P₂O₅ and 9% CaO, and not a rock phosphate. The quicker of the two phosphate sources, there for stolon growth and tuber set after emergence.
03Immediate release
Sulphate of potash — mineral, low chloride
50% K₂O in sulphate form, dissolving straight away to give the young crop its first potash. Also sold on its own as Sulphate of Potash.
04Immediate release
Gypsum (calcium sulphate) — mineral
23% calcium and 18.6% sulphur, both available at once. A neutral salt, so it adds calcium without raising soil pH.
05Sustained release
Micronised magnesium mineral — milled to about 5 microns
20.9% Mg, milled fine to weather readily. Magnesium sits at the centre of every chlorophyll molecule and helps move sugar from leaf to tuber.
06Slow release
Yorkshire polyhalite — North Yorkshire, mined mineral
One crystal carrying 14% K₂O, 17% CaO, 6% MgO and sulphate, mined more than a kilometre down in workings that run out under the North Sea. It releases more slowly than sulphate of potash, so supply carries on after the fast sources are spent. More on what polyhalite is.
07Slow release
Alfalfa meal — plant meal
Dried, milled lucerne: gentle nitrogen and organic matter that soil life works through over the season.
08Slow reserve
Micronised rock phosphate — mined mineral
31% P₂O₅ and 49% CaO. It dissolves slowly, so it is the phosphate still on hand when maincrops are bulking in August.
09Moderate release
Magnesium carbonate — mineral
20% Mg and the quickest of the three magnesium sources. It dissolves within weeks in moist soil and covers the early season while the other two build.
10Slow release
Scottish seaweed meal — hand-harvested
More than 60 trace elements, plus alginates that help the ridge hold its structure and moisture.
11Slow release
Rapeseed meal — British
The pressed meal left after oil extraction. Microbes release its nitrogen gradually and use it as a carbon source.
12Slow release
Mealworm frass — from farmed mealworms
Modest nitrogen and potash, plus chitin from shed skins, which feeds the soil microbes that break it down.
13Chelation
Humic and fulvic acid
Humic substances hold micronutrients in forms roots can use, and reviews link them to more lateral root growth and better nutrient uptake. Fulvic acid is the smaller, more soluble fraction.
14Permanent
Fermented biochar — British
Charcoal made for soil, fermented before blending. Its porous structure lasts, and in a 45-week study of manure-amended soil the highest biochar rate cut nitrogen leaching by 11% and dissolved phosphorus by 69% (Laird et al., 2010).
15Permanent reservoir
Clay minerals — British montmorillonite and illite
Clay surfaces hold potassium, calcium and magnesium and release them gradually, most usefully on light, sandy soils.
16Biostimulant
Seaweed extracts — British coastal
The soluble fraction of seaweed, carrying cytokinins, auxins and betaines, though how they work in the field is still being pinned down.
17Slow weathering
Volcanic rock dust — ground basalt
Weathers slowly, releasing iron, zinc, copper, manganese and silicon over years.
18Living culture
EM-1 microorganisms
A mixed culture of bacteria and yeasts, lactic acid bacteria among them, that gets the meals and minerals breaking down in the soil. Also sold as EM-1 Effective Microorganisms.
19Structural
Silica meal — mineral
A source of silicon, which plants lay down in their cell walls, where it stiffens the tissue.
20Plant-derived
Herbal mixture — comfrey, nettle, yarrow and chamomile
Comfrey is the gardener's traditional potash plant, nettle brings iron and silica, and yarrow and chamomile are the classic compost herbs. Count it as a biological extra; it adds little in the way of nutrients.
How to Use
How to use potato fertiliser: rates, timing and method
Before you start
This product is a milled powder with a bulk density of 1 g/ml, so grams and millilitres are interchangeable. Never apply it in direct contact with seed tubers: always mix it into the surrounding soil with a 10 cm gap. Water thoroughly after application. For best results, mix 1:1 with compost before applying.
Step-by-step: containers and grow bags
- Prepare your compost. 5–7.5g per litre, mixed thoroughly: 5g/L for enriched compost, 7.5g/L for plain or peat-free mixes.
- Fill and plant. Fill to half depth with the prepared compost. Set the seed tuber eyes upward and cover with 10–15cm.
- Earth up as shoots emerge. When shoots are 10–15cm tall, add compost, leaving 5cm exposed. Add 1.5–2.5g per litre of added compost.
- Continue until full. Include the top-dress dose each time. Once the container is full, switch to surface top-dressing.
- Surface top-dress every 3–4 weeks. 1.5–2.5g per litre of container volume, 10cm from the stem. Scratch it in and water. Our guide on how to top dress covers the technique.
- Monitor plant signals. Very dark haulm with few flowers: stretch to 5–6 weeks. Pale lower leaves from midsummer are normal remobilisation.
Application rates
Containers, grow bags & pots
| Situation | Rate (g = ml) | Frequency | Notes |
|---|---|---|---|
| Potting mix preparation | 5–7.5g per litre | Once at planting | 5g/L enriched mixes. 7.5g/L plain or peat-free. |
| Container top-dressing | 1.5–2.5g per litre of pot volume | Every 3–4 weeks | 1.5g/L earlies. 2–2.5g/L maincrops. |
Outdoor beds, raised beds & allotments
| Situation | Rate (g = ml) | Frequency | Notes |
|---|---|---|---|
| Initial soil preparation | 125–175g per m² | Once before planting | Fork into top 15–20cm. 175g/m² for depleted beds. |
| Outdoor top-dressing | 100–150g per m² | Every 3–4 weeks | 100g/m² earlies. 150g/m² maincrops through bulking. |
| Single plant at planting | 30–45g per plant | Once at planting | Mix into planting hole. 10cm gap from tuber. |
| Single plant top-dressing | 20–35g per plant | Every 3–4 weeks | Ring 10–15cm from stem. Time with earthing up. |
Seasonal feeding guide
| Stage | Timing | Rate & frequency | Goal |
|---|---|---|---|
| Bed / container prep | 2–4 weeks before planting | Beds: 125–175g/m². Pots: 5–7.5g/L | Build nutrient-rich root zone |
| At planting | At time of planting | 30–45g per planting position | Localised nutrition for emerging stolons |
| First earthing up | 3–4 weeks after emergence | Beds: 100–150g/m². Pots: 1.5–2.5g/L | K and P into tuber initiation zone |
| Active bulking | 4–6 weeks after tuber initiation | Same, every 3–4 weeks | Sustained K for starch accumulation |
| Ripening & curing | Haulm yellowing | Stop or single low-rate application | Allow skin set; excess N reduces storage life |
Works well combined with…
Use Dr Forest Seaweed Powder as a fortnightly foliar. Apply Dr Forest Liquid Gypsum as a root drench for additional calcium during tuber initiation. Use the Dr Forest All-Purpose 4-4-4 for companion plantings.
Storage
Cool, dry place out of direct sunlight. Keep sealed. Effective for at least 18 months.
Growing Guide
Potato growing guide — earlies, maincrops, chitting, earthing up and feeding by type
Potatoes are easy to grow and easy to grow badly. Most of the difference is timing: which type you plant, when, how evenly the ridge stays moist and when you stop feeding. Written for UK gardens and allotments.
First earlies, second earlies and maincrops
First earlies — new potatoes, the quickest crop
- Plant mid-March in mild areas, late March elsewhere; lift in June and July, about 10–12 weeks after planting
- Rocket, Swift, Casablanca, Lady Christl, Pentland Javelin
- 30cm apart in rows 60cm apart
- Lower feeding rates, 1–2 top-dresses at most
Second earlies — salad and summer potatoes
- Plant in April and lift in July and August, spaced as first earlies
- Charlotte, Anya, Nicola, Kestrel, International Kidney (Jersey Royal when grown on Jersey); lower to mid-range feeding, 1–2 top-dresses
Maincrops — the potatoes you store
- Plant in April, or into early May; lift from late August to October
- Floury: King Edward, Maris Piper, Rooster, Kerr's Pink, Golden Wonder. All-rounders: Desiree, Cara, Sarpo Mira
- 37cm apart in rows 75cm apart; floury types at the upper end of the range, all-rounders mid-range, 2–3 top-dresses through bulking
Feeding adjustments by variety type
First earlies — Rocket, Swift, Casablanca, Lady Christl, Pentland Javelin
Short season (10–12 weeks). Full base dressing, then 1 top-dress at first earthing up; a second only if the season is long. Lifted before starch builds fully, they need less potash than maincrops.
Second earlies & salad — Charlotte, Anya, Nicola, Kestrel, International Kidney (Jersey Royal)
Waxy varieties bred for firm texture. Moderate feeding keeps the waxy character. Harvest when the haulm just begins to yellow.
Floury maincrops — King Edward, Maris Piper, Rooster, Kerr's Pink, Golden Wonder
What this formula was designed for. Floury varieties are bred for high starch but only get there with potassium supplied steadily through a long bulking period. Full programme, upper rates.
All-rounders — Desiree, Cara, Sarpo Mira, Wilja, Estima
Versatile varieties that respond well to standard rates. Wilja and Estima are second earlies, the rest maincrops. Sarpo Mira has exceptional blight resistance and benefits from the full maincrop programme.
Heritage & specialist — Pink Fir Apple, Shetland Black, Highland Burgundy Red, Ratte, Salad Blue
Grown for flavour and looks rather than weight of crop; Pink Fir Apple, for one, is a late maincrop. A bigger dose won't turn a light-cropping variety into a heavy one.
Chitting — do you need to?
Optional, but worth it for earlies
Chitting (pre-sprouting) gives first and second earlies a 2–3 week head start; it matters less for maincrops. Stand tubers upright in egg boxes in a cool (8–10°C), bright room from late January and plant when sprouts are 1.5–2.5cm long. A chitting tuber runs on its own starch and needs no fertiliser.
Containers and grow bags vs beds and allotments
Containers, grow bags and patio pots
- Best for first and second earlies
- Earth up by adding compost in layers; feed at every earthing up, then surface top-dress every 3–4 weeks
- Water daily in warm weather, and make sure the container drains freely
Outdoor beds, raised beds and allotments
- Every type, from first earlies to late maincrops
- Earth up by drawing soil from between the rows, and mulch after the final earthing up
- Water deeply 2–3 times a week in dry spells
- Don't grow potatoes or tomatoes in the same bed two years running
Watering while tubers form
A dry spell while tubers are forming leaves fewer of them; drought followed by a soaking gives cracked, knobbly or hollow ones. Tubers usually start forming around the time the first flower buds appear, and from then through bulking steady moisture counts most.
01
Containers and grow bags
Check daily from June; a full-grown plant can drink a bag dry on a warm afternoon. Water until it drains through, and after every top-dress.
02
Beds and allotments
A good soak two or three times a week in dry weather beats a daily sprinkle that only wets the surface. Aim at the base of the ridge.
Calcium moves with water
Calcium travels with water, and most of that goes to the leaves. Tubers take theirs from the soil right around them, through small roots on the stolons and tubers (Palta, 2010), so feed into the ridge and keep it moist.
Earthing up — why and when
- Keeps tubers dark. Tubers that see light turn green and build up bitter glycoalkaloids (solanine).
- Puts the feed where the tubers are. Apply your top-dress dose just before or during earthing up.
- When to earth up. First time when shoots reach 15–20cm. Second time 2–3 weeks later, when the shoots re-emerge. Container growers add compost layers instead of drawing soil.
- Cover against late frost. If frost is forecast in April or May, draw soil over emerging shoots or cover them overnight with hessian or straw.
UK seasonal timeline
| Month | Task | Feeding |
|---|---|---|
| Jan–Feb | Order seed tubers. Chit earlies at 8–10°C, bright but out of direct sun. | None |
| March | Prepare beds 2–4 weeks before planting. Plant first earlies mid-March in mild areas, late March elsewhere. | Fork in 125–175g/m² base dressing |
| April | Plant second earlies and maincrops (maincrops until early May). Prepare containers. | 30–45g per planting hole. Containers: 5–7.5g/L charged compost |
| May | First earthing up when shoots reach 15–20cm. Keep the soil moist. | First top-dress (100–150g/m²) during earthing up |
| June | Second earthing up. Lift earlies when the flowers open or the haulm begins to yellow. | Continue top-dressing every 3–4 weeks |
| July | Lift first and second earlies. Watch the blight forecast in warm, humid weather. | Maincrops: upper end, every 3 weeks |
| August | Reduce watering slightly in the last 2 weeks before lifting. Cut the haulm if blight appears. | Final top-dress for maincrops |
| Sep–Oct | Lift maincrops on a dry day, leave on the soil 1–2 hours to dry, then store cool, dark and ventilated in hessian or paper sacks. | None |
Common problems
Lots of leaf, few tubers
Very dark, lush haulm with few flowers is the sign. Skip the next top-dress, reduce rates and stretch the interval to 5–6 weeks.
Hollow heart
Water and feed evenly through bulking. Big-tubered maincrops such as King Edward and Maris Piper suffer most; the cavity is harmless.
Green tubers
Earth up thoroughly, re-cover ridges after heavy rain and store the crop in the dark. Green potatoes should not be eaten.
Common scab
Keep the ridge moist for the first few weeks after tubers form, don't lime ahead of potatoes and choose a scab-resistant variety if your ground is prone. If your pH runs high, see our guide to changing soil pH. The marks are skin-deep.
Potato blight
No fertiliser keeps blight away. Grow resistant varieties (Sarpo Mira, Sarpo Axona, Carolus) and follow the Hutton Criteria forecast. If blight appears, cut the haulm to ground level at once and don't compost it; tubers are usually fine if the haulm comes off promptly.
The Science
The science of starch, flavour and the potato tuber — and why feeding matters
A tuber is a starch store the plant fills with sugar made in its leaves, and texture and flavour depend on how well that filling went. Flavour starts as precursors the plant builds, mainly sugars, amino acids, RNA and lipids, which cooking turns into the compounds you taste; variety, growing conditions and storage all shift them (Jansky, 2010).
Why the 3-5-8 ratio works
Potatoes hold more potassium than any other major nutrient, about 1.7% of dry matter, and a 30 t/ha crop removes around 250 kg of it per hectare (Torabian et al., 2021; Koch et al., 2020). A high nitrogen supply can delay or suppress tuber formation (Koch et al., 2020). Hence a K:N ratio of 2.7:1, with 5% phosphate for tuber set.
3-5-8NPK ratio
1.7%K in tuber dry matter
250 kgK per ha, 30 t crop
−2%Starch with muriate
For starch, the rate potassium reaches the tuber matters more than the total it holds.
What makes a potato taste like a potato
| Compound | What it does | Feeding link | Source |
|---|---|---|---|
| Starch and dry matter | Floury or waxy texture | Potassium activates starch synthase; potassium chloride gave about 2% less starch than sulphate | Nitsos & Evans, 1969; Torabian et al., 2021; Naumann et al., 2020 |
| Sugars | Sweetness; browning when roasted or fried | Exported from the leaves to the tuber, an export that magnesium shortage holds back | Jansky, 2010; Hauer-Jákli & Tränkner, 2019 |
| Glutamate and 5'-nucleotides | Savoury (umami) depth; tracked panel flavour-intensity scores (R² 0.83) | Differed mainly by variety in this study, which did not test feeding | Morris et al., 2007 |
| Tuber calcium | Cell-wall strength; low levels linked to hollow heart and internal brown spot | Taken up from the soil around the tuber | Palta, 2010; Naumann et al., 2020 |
Why a slow-release, multi-input feed suits potatoes
01
Potassium builds the starch, and timing matters
In the classic study, adding potassium strongly raised starch synthase activity in potato and other crops, and the sweet corn enzyme could not work without it (Nitsos & Evans, 1969); potato reviews link potassium to higher starch (Torabian et al., 2021). In tubers, the rate of potassium arriving tracked starch production more closely than the total held (Lindhauer & De Fekete, 1990). Hence fast sulphate of potash, slower polyhalite and a top-dress every 3–4 weeks.
02
Sulphate beats muriate for starch
In a German trial reported by Naumann et al. (2020), potassium chloride cut starch by about 2% and starch yield by about a tonne per hectare compared with the sulphate form, and a second review found the sulphate better for dry matter and starch (Torabian et al., 2021).
03
Nitrogen in proportion
High nitrogen can delay tuberisation and favours stems over tubers (Koch et al., 2020). Too little is no answer either: a lower nitrogen supply can raise reducing sugars by 60–100% (Naumann et al., 2020), which matters if you roast or fry. So 3%, released gradually as the meals and minerals break down.
04
Phosphate for tuber set
Phosphorus has a significant effect on tuber setting, especially early in growth (Koch et al., 2020): calcined plant meal covers the first weeks, rock phosphate the late season.
05
Calcium comes from the ridge
Calcium moves with water in the xylem and little of that water reaches the tubers, which rely on roots growing from the stolons and the tubers themselves. In-season calcium raised tuber calcium and lowered hollow heart, internal brown spot and bruising in Palta's work (Palta, 2010).
06
Magnesium moves the sugar
Under magnesium shortage, sucrose transport from leaves to sink organs is inhibited and sugars pile up in the leaves (reviewed by Hauer-Jákli & Tränkner, 2019). In a potato the main sink is the tuber.
07
Organic matter feeds soil biology
Across 56 studies, organic systems carried 32–84% more microbial biomass and activity than conventional ones (Lori et al., 2017). In a 45-week column study of manure-amended soil, biochar cut nitrogen leaching by 11% and dissolved phosphorus by 69% (Laird et al., 2010). Humic substances are linked to more lateral root growth (Canellas et al., 2015); seaweed carries growth-active compounds whose mode of action is still poorly understood (Khan et al., 2009).
What we don't claim
Across three field experiments, polyhalite improved potato skin appearance only moderately, and mainly when applied after the haulm had been desiccated; earlier applications did not change the peel's mineral make-up (Keren-Keiserman et al., 2019). So we don't promise better skins. Nor better taste from growing organically: over four years and eight varieties, organic tubers were lower in nitrate and higher in vitamin C, but glycoalkaloids ran higher in some and taste panels found no significant difference (Hajšlová et al., 2005).
Study data
| Study | Scope | Finding |
|---|---|---|
| Naumann et al. (2020) | Review; KCl data from one German trial (2003) | Potassium chloride: starch about 2% and starch yield about 1 t/ha lower than sulphate |
| Palta (2010) | Review of the author's calcium research | In-season calcium: higher tuber calcium, less hollow heart and internal brown spot |
| Hajšlová et al. (2005) | Eight varieties, four harvests | Organic: lower nitrate, more vitamin C; no significant taste difference |
Scientific references
- Torabian, S., Farhangi-Abriz, S., Qin, R. et al. (2021). Potassium: a vital macronutrient in potato production — a review. Agronomy, 11(3), 543.
- Koch, M., Naumann, M., Pawelzik, E. et al. (2020). The importance of nutrient management for potato production Part I: plant nutrition and yield. Potato Research, 63(1), 97–119.
- Naumann, M., Koch, M., Thiel, H. et al. (2020). The importance of nutrient management for potato production Part II: plant nutrition and tuber quality. Potato Research, 63(1), 121–137.
- Lindhauer, M.G. & De Fekete, M.A.R. (1990). Starch synthesis in potato (Solanum tuberosum) tubers: activity of selected enzymes in dependence of potassium content in storage tissue. Plant and Soil, 124(2), 291–295.
- Nitsos, R.E. & Evans, H.J. (1969). Effects of univalent cations on the activity of particulate starch synthetase. Plant Physiology, 44(9), 1260–1266.
- Palta, J.P. (2010). Improving potato tuber quality and production by targeted calcium nutrition: the discovery of tuber roots leading to a new concept in potato nutrition. Potato Research, 53(4), 267–275.
- Keren-Keiserman, A., Singh Baghel, R., Fogelman, E. et al. (2019). Effects of polyhalite fertilization on skin quality of potato tuber. Frontiers in Plant Science, 10, 1379.
- Jansky, S.H. (2010). Potato flavor. American Journal of Potato Research, 87(2), 209–217.
- Morris, W.L., Ross, H.A., Ducreux, L.J.M. et al. (2007). Umami compounds are a determinant of the flavor of potato (Solanum tuberosum L.). Journal of Agricultural and Food Chemistry, 55(23), 9627–9633.
- Lori, M., Symnaczik, S., Mäder, P. et al. (2017). Organic farming enhances soil microbial abundance and activity — a meta-analysis and meta-regression. PLOS ONE, 12(7), e0180442.
- Laird, D., Fleming, P., Wang, B. et al. (2010). Biochar impact on nutrient leaching from a Midwestern agricultural soil. Geoderma, 158(3–4), 436–442.
- Khan, W., Rayirath, U.P., Subramanian, S. et al. (2009). Seaweed extracts as biostimulants of plant growth and development. Journal of Plant Growth Regulation, 28(4), 386–399.
- Canellas, L.P., Olivares, F.L., Aguiar, N.O. et al. (2015). Humic and fulvic acids as biostimulants in horticulture. Scientia Horticulturae, 196, 15–27.
- Hajšlová, J., Schulzová, V., Slanina, P. et al. (2005). Quality of organically and conventionally grown potatoes: four-year study of micronutrients, metals, secondary metabolites, enzymic browning and organoleptic properties. Food Additives and Contaminants, 22(6), 514–534.
- Hauer-Jákli, M. & Tränkner, M. (2019). Critical leaf magnesium thresholds and the impact of magnesium on plant growth and photo-oxidative defense: a systematic review and meta-analysis from 70 years of research. Frontiers in Plant Science, 10, 766.
Figures describe the published literature on these ingredient classes and are not product-specific yield guarantees.
Questions & Answers
Frequently asked questions about potato fertiliser
A potash-led feed with moderate nitrogen, its potash in sulphate form, and calcium and magnesium alongside, which is what this 3-5-8 blend is built to be. Feed before planting and at earthing up, and keep the ridge moist: no feed makes up for a dry July.
More potash than nitrogen. Potatoes hold more potassium than any other major nutrient, and a high nitrogen supply can delay tuber formation (Koch et al., 2020). This feed is 3-5-8, a K:N ratio of 2.7:1, with 5% phosphate for tuber set.
On rich, well-manured ground you'll get a crop without it. In most allotment soils, grow bags and containers, feeding pays: a good crop removes about 25 g of potassium from every square metre (Torabian et al., 2021), and bagged compost runs short long before a maincrop finishes.
Into the bed or container 2–4 weeks before planting, at planting, at first earthing up (3–4 weeks after emergence), then every 3–4 weeks through active bulking. At haulm yellowing, stop or give a single low-rate application. Rates for each stage are on the How to Use tab.
Yes. Earlies: lower rates, 1–2 top-dresses. Maincrops: upper rates, 2–3 top-dresses through bulking. Same base dressing for both. The Growing Guide tab breaks it down by variety type.
Yes. Use 5g/L rather than 7.5g/L for the initial mix, and begin top-dressing at 6–8 weeks rather than immediately at first earthing up.
That is excess nitrogen relative to potassium. Skip the next top-dress, reduce rates and stretch to 5–6 weeks. It is common in recently manured soil.
Because the chloride form costs starch. In a German trial reported by Naumann et al. (2020), potassium chloride gave about 2% less starch and around a tonne less starch per hectare than the sulphate form. The mineral potash here comes from sulphate of potash and Yorkshire polyhalite, which is also sold on its own as Polyhalite Fertiliser.
Don't buy it for that. Scab comes down to growing conditions: it is worst when the soil dries out while tubers are forming, and on alkaline or freshly limed ground. Keep the ridge moist in those weeks, don't lime ahead of potatoes and pick a scab-resistant variety if your soil is prone.
Yes. Potato roots partner with arbuscular mycorrhizal fungi, and an inoculant such as our mycorrhizal fungi powder can go in alongside this feed: apply it as its own label directs and keep this feed the usual 10 cm from the seed tuber. See our guide to mycorrhizal fungi.
Yes. It is made from organic and mineral ingredients, and there is no withholding period before harvest. Dogs like the smell of meal-based feeds, so fork it in, water it and keep the bag closed.
It is made with organic and natural ingredients (plant meals, seaweed, mealworm frass, mined minerals, humic substances and a live microbial culture) and no GMO inputs. The finished blend is not registered with an organic certification body, so there is no certification logo on the bag.
The high potash and moderate nitrogen suit sweet potatoes broadly; use lower rates. It was designed for Solanum tuberosum, though. For a mixed vegetable plot the Fruit & Vegetable Fertiliser 4-5-6 fits better, and tomatoes, which belong to the potato family, have their own tomato fertiliser.
For beds and allotments, fork 125–175 g per m² into the top 15–20 cm before planting (175 g for depleted ground), then top-dress at 100–150 g per m² every 3–4 weeks: 100 g for earlies and 150 g for maincrops through bulking. For single plants, mix 30–45 g into the planting hole, keeping it 10 cm from the tuber. In containers and grow bags, top-dress at 1.5–2.5 g per litre of pot volume every 3–4 weeks. Feed generously for big maincrop tubers, but don't overdo the nitrogen.
Customers also bought
48% of buyers here also chose Organic Tomato Fertiliser
Fertiliser
Fruit & Vegetable Fertiliser (Veg Feed) 4-5-6
A balanced 4-5-6 feed for fruit and veg.
from £11.50
Fertiliser
Chilli & Pepper Fertiliser | Organic 3-3.5-7
A balanced slow-release feed for chillies and peppers.
from £11.50
