Potash & Potassium Fertilisers

Potash and potassium: what they do and who needs them

Potassium runs the plumbing of a plant. It governs how water moves, how sugars are made and stored, and how well a plant stands up to drought, cold and stress. In the garden that shows up as fruit size and flavour, flower colour, and the difference between a tomato that splits and one that does not. A high potash fertiliser is the feed for anything that flowers or fruits, and the thing to reach for when a plant has plenty of leaf and not much else. Everything here is chloride-free; potassium chloride is cheap but hard on soil life and on sensitive crops like strawberries and potatoes, and we do not use it.

The straight potassium sources

• Sulphate of Potash, 50% K₂O. The concentrated option: a mined mineral potassium sulphate, sprinkled around fruit trees, tomatoes and flowering shrubs, or worked into the potato bed. Polyhalite versus sulphate of potash explains when to choose it.
• Potassium Rich Fertiliser, 11% K. A potassium plant food at a gentler analysis, easier to spread evenly and kinder on seedlings.
• Organic Liquid Potassium Feed, 15% K₂O. The chloride-free liquid potash for containers and for a quick lift at flowering and fruit set.
• Polyhalite. Mined in Yorkshire: potassium with calcium, magnesium and sulphur in the same slow-release granule. What is polyhalite has the geology and the numbers.

The crop feeds that lean towards potassium

If you would rather buy one blend than balance your own, Organic Tomato Fertiliser 3-4-6, Strawberry Fertiliser and the liquid Organic Liquid Fertiliser 3-2-6 are all built with potassium ahead of nitrogen, which is the shape a fruiting plant wants from first flower onwards. The full set of crop blends is in tomatoes and edibles.

Common questions