The short version
Fertiliser is not plant food: plants make their own food from light. Fertiliser supplies the minerals they build with. Soil worked with compost supplies most of it, and the plants that need more are the ones cropping heavily over a long season.
What you need
Compost or well-rotted manure
The base. Worked in before planting, it carries most crops through.
A general feed
Balanced N-P-K for growth. Used when growth is the goal.
A high-potassium feed
For flowering and fruiting. Tomato feed is the common one, and it suits anything that fruits.
How to do it
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Feed the soil first
Compost before planting does more than any liquid feed applied later.
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Match the feed to the stage
Nitrogen for leaves, potassium for flowers and fruit. Feeding nitrogen to a fruiting plant gives you a big green plant and little crop.
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Start feeding when the plant starts working
For fruiting crops, usually once the first flowers set, not before.
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Follow the dilution on the bottle
Stronger is not better. Over-feeding scorches roots and pushes soft growth that pests find first.
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Stop feeding towards the end
Late feeding pushes soft growth into cold weather, which is exactly what does not survive it.
When it goes wrong
Pale, small leaves
- Nitrogen
Often nitrogen shortage, but check pH first: locked-up nutrients look identical to absent ones.
Lush leaves, no fruit
- Too much nitrogen
Too much nitrogen, not enough potassium. Switch feeds.
Brown scorched leaf edges
- Over-feeding
Fertiliser burn or salt build-up in containers. Flush the pot through with plain water.
Frequently asked questions
Do I need to feed at all?
In soil enriched with compost, many crops need nothing. Heavy feeders in containers need it most, because there is no reserve.
Organic or synthetic?
Plants take up the same ions either way. Organic feeds release slowly and feed the soil life as well, which matters over years.
