• Organic Potassium Fertiliser — pile of fine pale-cream potassium powder
  • Organic Potassium Fertiliser — 150g kraft pouch with dr forest Micro-K 11% Potassium, Micronised Potassium Mineral
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Dr Forest

Potassium Rich Fertiliser 11% K

£6.99
£6.99
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  • ✓Free UK delivery on orders over £40
  • ✓Handcrafted and dispatched from Stockport
  • ✓Made with organic ingredients
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Micro-K — micronised potassium rock dust, 11% K₂O, solution-grade mineral fertiliser

11% K₂O Potassium Micronised Powder Solution Grade Foliar & Soil Drench Organic Approved Quarry-Extracted

Potassium is the nutrient that drives fruit quality, flavour development, disease resistance, and water regulation. Most potassium fertilisers are soluble salts — they deliver a sharp pulse of K that peaks fast and leaches within days. Micro-K is different. It is a potassium-rich mineral rock dust, quarry-extracted and micronised to solution-grade fineness, delivering 11% K₂O in a form that releases gradually as the particles dissolve in soil moisture.

The ultra-fine particle size means it can be suspended in water for foliar spraying and soil drenching — giving you the flexibility of a liquid feed with the sustained release characteristics of a mineral amendment. It can also be broadcast directly onto soil for long-term potassium building. Chloride-free, no synthetic processing, organic approved.

11%K₂O (Potash)
MicronisedSolution Grade
Foliar& Soil Drench
NaturalMineral Origin

What Micro-K is used for in the garden

  • Fruiting and flowering crops — potassium regulates sugar transport, fruit ripening, and flower colour intensity; essential for tomatoes, strawberries, peppers, roses, and all fruiting plants
  • Flavour and quality improvement — adequate potassium increases soluble sugar content, vitamin C, and dry matter in fruit and vegetables
  • Drought and frost resistance — potassium regulates stomatal opening and cell turgor pressure, reducing water loss and improving survival under temperature extremes
  • Disease resistance — potassium strengthens cell walls, increases cuticle wax deposition, and activates plant defence enzymes
  • Soil remineralisation — broadcast application rebuilds potassium reserves in depleted soils, with a slower, more sustained release profile than soluble K salts
  • Foliar potassium for rapid response — the micronised particle size allows suspension in water for direct foliar application during peak demand or visible deficiency
  • Lawn winter hardening — potassium toughens turf against frost, improves wear tolerance, and supports root development ahead of winter dormancy
  • Long-term soil building — unlike soluble potassium which leaches rapidly, mineral-bound K releases as soil biology and root exudates break down particles over the growing season

Why micronised rock potassium instead of soluble potash?

Micronised Potassium Rock Dust — Micro-K

  • Natural mineral — quarried, ground, and packaged with no chemical processing
  • Sustained release — potassium held in mineral matrix, released gradually
  • Micronised to solution-grade — suspends in water for foliar or drench use
  • Also effective as a dry broadcast for long-term soil K building
  • Contains trace minerals from the parent rock alongside potassium
  • Low salt index — no risk of root burn or salt stress

Sulphate of Potash / Muriate of Potash

  • Higher K₂O concentration (50–60%) — more potassium per gram
  • Fully soluble — fast-acting but leaches rapidly in rain and watering
  • Higher salt index — greater risk of root burn in confined volumes
  • MOP adds chloride; SOP adds sulphur — additional considerations
  • Ideal for acute deficiency correction or peak-demand supplementation
  • Best used in combination with slower-release mineral sources
Handcrafted in Stockport

Every Dr Forest product is made by hand in small batches at our workshop in Stockport, Greater Manchester. We source ingredients for quality, not cost. Recyclable packaging on the 1.5 kg, 3 kg, and 9 kg sizes.

The science of potassium in plant nutrition

The quality nutrient

Potassium is the most abundant cation in plant tissue and the single most important nutrient for fruit quality. It does not become part of organic molecules — instead it operates as a free ion, regulating water pressure, activating over 60 enzymes, balancing electrical charges, and transporting sugars from leaves to developing fruit. Plants deficient in potassium produce smaller, less flavourful fruit with reduced shelf life and weaker resistance to disease.

01

Sugar Transport & Fruit Quality

Potassium is essential for phloem loading — the active process by which sucrose is pumped into the phloem for transport to developing fruit, roots, and storage organs. Potassium-deficient plants accumulate sugars in leaves while fruit remains undersized, under-sweetened, and poorly coloured. This is why potassium is called the "quality nutrient" — it does not increase the quantity of growth so much as the quality of what is produced.

02

Stomatal Regulation & Drought Tolerance

Potassium is the primary ion controlling stomatal aperture. Guard cells accumulate K⁺ to increase turgor and open stomata for gas exchange; they release K⁺ to close stomata and conserve water under drought stress. Plants with adequate potassium respond faster to water stress, lose less water per unit of CO₂ fixed, and recover more quickly from drought episodes. This makes potassium the most important nutrient for water use efficiency.

03

Disease Resistance & Cell Wall Strength

Potassium strengthens cell walls by promoting lignin and cellulose synthesis, increases cuticle wax deposition, and activates pathogenesis-related (PR) proteins. Potassium-sufficient plants show reduced incidence of fungal diseases including powdery mildew, botrytis, and fusarium wilt. The mechanism is physical — stronger cell walls resist penetration by fungal hyphae — combined with faster enzymatic defence cascades.

04

Frost Hardiness

Potassium lowers the freezing point of cell sap by increasing solute concentration, maintaining membrane integrity under temperature extremes. Autumn applications of potassium are standard practice in professional turf management and orchard care specifically to harden tissue against winter frost damage.

05

Micronised Rock Dust — Sustained Release

In soluble form (SOP, MOP), potassium is immediately available but highly mobile in soil solution — it leaches rapidly in rain and irrigation, particularly in sandy and container soils. Potassium held within a mineral rock matrix releases as the particle surface dissolves in soil moisture and is attacked by root exudates and microbial organic acids. The micronisation of Micro-K dramatically increases the surface area available for this dissolution, accelerating release compared to coarse rock dust while maintaining the sustained-availability advantage over fully soluble salts.

06

Deficiency Symptoms

Potassium is phloem-mobile, so deficiency symptoms appear on older leaves first. The classic sign is marginal leaf scorch — brown, dry edges on lower leaves that progress inward. Other symptoms include poor fruit set, small fruit, weak stems, and increased susceptibility to disease and frost damage. In lawns, potassium deficiency manifests as poor winter survival and slow spring recovery.

Scientific References

  1. Mengel, K. & Kirkby, E.A. (2001). Principles of Plant Nutrition. 5th ed. Kluwer Academic.
  2. Marschner, P. (2012). Marschner's Mineral Nutrition of Higher Plants. 3rd ed. Academic Press.
  3. Wang, M. et al. (2013). The critical role of potassium in plant stress response. Int. J. Mol. Sci., 14, 7370–7390.
  4. Pettigrew, W.T. (2008). Potassium influences on yield and quality production for maize, wheat, soybean and cotton. Physiologia Plantarum, 133(4), 670–681.

How to use Micro-K: application rates & guide

Solution-grade micronised powder

Micro-K suspends in water for foliar spraying and soil drenching. Stir or shake well before and during application — as a mineral suspension it will settle over time. It can also be broadcast directly onto soil as a dry amendment for long-term potassium building.

Application rates

Soil drench — liquid application

Rate: 0.5–1g per litre of water  |  Frequency: Every 2–4 weeks during the growing season

Suspend in water and apply to the root zone. Particularly useful during peak fruiting and flowering when potassium demand spikes. Use at the higher rate for heavy-feeding crops like tomatoes and peppers.

Foliar spray — rapid potassium delivery

Rate: 0.5–1g per litre of water  |  Frequency: Every 7–14 days during fruiting

Spray both leaf surfaces in early morning or late evening. Stir the solution regularly during spraying to maintain suspension. Foliar potassium is absorbed rapidly and can supplement root uptake during peak demand.

Soil broadcast — dry application for beds and borders

Rate: 150–350g per m²  |  Frequency: Once or twice per year

Scatter evenly and work into the top layer if possible. Water in. The micronised particles release potassium gradually as they dissolve in soil moisture. Use the higher rate for known-deficient soils or heavy-feeding crops.

Trees and shrubs

Rate: 5–15 kg per plant  |  Frequency: Annually in spring or autumn

Spread around the drip line and work into the soil. Water in thoroughly. Particularly important for fruit trees, vines, and ornamental trees where potassium supports fruit quality and winter hardiness.

Lawns and turf

Rate: 50–150g per m²  |  Frequency: Twice per year — spring and autumn

Broadcast evenly and water in. The autumn application is particularly important for winter hardening. Potassium improves frost tolerance, wear resistance, and spring recovery.

Step-by-step preparation for liquid application

  1. Measure the powder. For a 10-litre watering can, measure 5–10g (1–2 level teaspoons).
  2. Add to water and stir vigorously. The micronised powder suspends in water but will settle over time. Stir or shake regularly during application.
  3. Apply to foliage or root zone. For foliar sprays, use a sprayer with good agitation. For root drenches, apply evenly around the base of the plant.
  4. Time to demand. Potassium demand peaks during flowering and fruit development. Begin supplementing when the first flowers appear and continue through to harvest.
  5. Store dry powder sealed. Keep in a cool, dry place. Shelf life is indefinite when kept dry.
Works well combined with…

For higher-concentration soluble potassium during peak fruiting, combine with Sulphate of Potash (50% K₂O). Use alongside Yorkshire Polyhalite for balanced K, Ca, Mg, and S. Pair with Micro-Mag to maintain K:Mg balance — high potassium can induce magnesium deficiency if Mg is not also supplemented. Add Seaweed Powder for biostimulant activity.

Frequently asked questions about Micro-K

Micro-K is a natural rock dust, not a refined salt. The potassium is bound within the mineral matrix and releases gradually as particles dissolve in soil moisture. Sulphate of potash is a concentrated soluble salt — higher K per gram but it leaches faster and has a higher salt index. The two products serve different purposes: Micro-K for sustained background potassium and soil building, SOP for acute supplementation during peak demand. Many growers use both.
Marginal leaf scorch on older leaves — brown, dry edges that progress inward. Because potassium is mobile in the plant, deficiency always appears on older leaves first as K is remobilised to new growth. Other signs include poor fruit set, small or poorly flavoured fruit, weak stems, and increased susceptibility to disease and frost damage.
Yes. The micronised particle size suspends in water for sprayer application. Stir or shake regularly during use as particles will settle. Foliar potassium is absorbed through the leaf surface and can supplement root uptake during periods of high demand. Spray in early morning or late evening for best absorption.
Yes. Micro-K is a natural mineral rock dust containing no chloride. It is safe for chloride-sensitive crops including tomatoes, strawberries, potatoes, grapes, and salad crops.
Yes. Natural quarry-extracted potassium-rich rock dust with no synthetic processing or chemical additives. Suitable for use in organic growing systems.
Yes. Potassium is essential for turf winter hardiness, drought tolerance, and wear resistance. Apply 50–150g per m² in spring and autumn. The autumn application is particularly important for hardening turf against frost and winter damage.
No — like all rock dust products, Micro-K forms a suspension rather than a true solution. The micronised particle size allows it to suspend effectively for spraying and drenching, but it will settle over time. Stir or agitate regularly during application. This is normal and does not reduce effectiveness.
Potassium and magnesium compete for root uptake sites. Very high potassium levels can suppress magnesium absorption, particularly in containers where the root zone is confined. If you are applying potassium heavily during fruiting, consider supplementing with Micro-Mag or Yorkshire Polyhalite (which contains both K and Mg) to maintain the balance.
The 1.5 kg, 3 kg, and 9 kg sizes are supplied in recyclable packaging. The 500g size is not currently in recyclable packaging.
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