What should I feed fruit trees and bushes, and when?

Fruit feeding is unusually simple because the requirement is lopsided. Potassium drives flowering, fruit set, fruit size and flavour; nitrogen drives leaf and shoot growth, which past a certain point actively suppresses fruiting and makes soft growth that scab, canker and aphids like. So the default fruit feed is high in potash and low in nitrogen, which is the opposite of a lawn feed and the reason a fruit tree in a fed lawn grows beautifully and fruits badly.

What you'll need

• Sulphate of potash
• Well-rotted manure, garden compost or bark mulch
• Sulphate of ammonia or a balanced fertiliser (optional)
• Ericaceous feed for blueberries (optional)
• Watering can (optional)

Step by step

1. Feed in late winter, February to early March, before growth starts.The feed needs to be in the soil and moving down when roots become active. Feeding in midsummer produces soft late growth that does not ripen before winter and gets damaged by frost.
2. Apply sulphate of potash across the whole root area.Roughly 15–20g per square metre, scattered over the ground beneath the canopy and a little beyond — not in a ring at the trunk, where there are few feeding roots. Rake it lightly into the surface and water it in if the weather is dry.
3. Add nitrogen only to the hungry crops.Plums, damsons, cooking apples, blackcurrants and raspberries respond to extra nitrogen — sulphate of ammonia at about 15–20g per square metre, or a balanced general fertiliser. Dessert apples, pears and gooseberries usually need none, and a tree already growing strongly certainly does not.
4. Mulch after feeding, onto wet soil.A 5–8cm layer of well-rotted manure or garden compost over a metre-wide circle for a tree, or over the whole row for soft fruit. Mulch on dry soil keeps the rain out; mulch on wet soil keeps the water in.
5. Keep mulch and grass off the stems.Leave 10cm of clear soil around a trunk or a bush's base. Mulch touching bark keeps it permanently damp and invites collar rot; long grass against a trunk hides voles and rabbits.
6. Clear the grass circle around young trees.Grass within a metre of a young or dwarf tree competes for exactly the water and nitrogen the tree needs and can halve growth. This makes more difference than any fertiliser you can buy.
7. Treat blueberries and other ericaceous fruit separately.They need an acidic feed and rainwater. Ordinary fertilisers and hard tap water raise the pH and lock up iron, which is why the leaves go yellow with green veins.
8. Feed containers on a completely different schedule.Pots have no reserve. Liquid high-potash feed weekly from bud break to late summer, or slow-release granules in spring, plus an annual top-dressing of fresh compost.
9. Watch the tree rather than the calendar.Long, soft, pale extension growth of 60cm or more with little blossom means too much nitrogen — stop feeding it. Short growth of under 15cm with small pale leaves and heavy small fruit means it is genuinely underfed.

Tips

• Wood ash is a useful free source of potash if it is kept dry until used, but it also raises pH — keep it away from blueberries entirely.
• Comfrey liquid is a genuinely high-potash homemade feed and works well on tomatoes, strawberries and container fruit.
• If a fruit tree stands in a lawn you feed, you are feeding the tree nitrogen every time. That alone explains a lot of vigorous, unfruitful trees.
• Never use lawn weed-and-feed anywhere near fruit: the herbicide component damages fruit trees and bushes, and aminopyralid residues in some manures do the same.
• On thin chalky or sandy soils, an annual mulch matters more than the fertiliser — organic matter is what holds both water and nutrients there.

Common mistakes

• Feeding a non-fruiting tree with general fertiliser — Most general feeds are nitrogen-led, which pushes growth at the expense of flower buds. It makes an unfruitful tree less fruitful, not more.
• Piling manure against the trunk — It holds moisture against the bark, softens the collar and invites rot and canker. Keep a clear collar of bare soil.
• Feeding in summer to rescue a poor crop — The crop is set months earlier. Late feeding produces soft autumn growth that frost damages and canker enters, and does nothing for this year's fruit.
• Using fresh manure — It scorches roots and robs nitrogen as it breaks down. It needs to be well rotted — at least a year old, dark, crumbly and without an ammonia smell.

Keeping on top of it

• Sulphate of potash across the root area of all fruit (Annually, late winter)
• Mulch trees and bushes over damp soil, stems left clear (Annually, after feeding)
• Nitrogen feed for plums, cookers, blackcurrants and raspberries (Annually, early spring)
• Keep a clear metre circle around young and dwarf trees (Check monthly in the growing season)
• Liquid high-potash feed for anything in a container (Weekly, April to August)

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