Potassium deficiency
Scorched, browning leaf margins on older leaves while the leaf centre stays green, with poor flowering and small, badly coloured fruit. It is most often seen on light sandy soils and on long-cropping container plants, where potassium is either washed out or simply used up.
What brings it on
Light, sandy or chalky soils where potassium leaches readily, and containers cropped for a long season without feeding. Heavy-fruiting plants have the highest demand.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Potassium deficiency
Checked 2026-08-13
Preventing it
Ordered by how much difference each measure actually makes, not by how often it is repeated.
- Feed long-cropping container plants through the season with a fertiliser formulated for fruiting, and incorporate organic matter on light soils to improve retention.
source
Sourced guidancemoderate confidence
- Royal Horticultural Society: Potassium deficiency — prevention
Checked 2026-08-13
Dealing with it once it is there
- Correct with a potassium-containing fertiliser applied at the rate its label states. The scorched margins on existing leaves do not recover; the test of whether it worked is the condition of the new growth.
source
Sourced guidancemoderate confidence
- Royal Horticultural Society: Potassium deficiency — treatment
Checked 2026-08-13
Signs that lead here
Each of these lists the other things that produce the same sign, and how to tell them apart.
On sprays and treatments
GrowingHQ does not tell anyone what to apply, at what rate, or how often. Pesticide approvals differ by country, change without notice, and the product label is legally binding — it is also the document you are holding. What is described here is cultural and physical control, which is what a home grower can act on without a label in front of them.