Fruit trees and berries are hungry plants, but they are hungry in a particular way: they need enough nutrition to grow strong wood and set fruit, and not so much that they grow soft, leafy shoots at the expense of fruit. The most common fertilising mistake in a fruit garden is too much nitrogen at the wrong time. A tree fed heavily in spring grows a mass of soft leaves, flowers poorly, and is more vulnerable to frost, aphids and disease. A tree fed modestly, with compost in spring and potash as the fruit swells, grows steadily and fruits well year after year.
The foundation of fruit feeding is not a bag of fertiliser but the soil itself. A soil rich in compost and organic matter holds nutrients, holds water, and feeds the soil life that makes nutrients available to roots. A mulch of compost each spring does more for most fruit than any fertiliser, and it is almost impossible to overdo. Chemical fertiliser has its place — for a quick correction, or for a hungry crop such as raspberries — but it should be the supplement, not the staple.
Before you feed anything, know what your soil already has. A soil test, available cheaply from a garden centre or through your extension service, tells you the pH and the levels of the major nutrients, and it stops you guessing. Blueberries, for example, need acidic soil, and feeding them with an ordinary fertiliser that raises the pH will do more harm than good. If you are unsure about a variety, a spray, or a diagnosis, check your local extension service — its advice is matched to your climate and soil.
What fruit actually needs: the three nutrients that matter
The three nutrients fruit needs most are nitrogen, phosphorus and potassium, usually called NPK. Nitrogen drives leafy growth and is needed in spring when the tree leafs out, but too much produces soft growth and little fruit. Phosphorus supports root growth and flowering, and is usually adequate in a soil with plenty of compost. Potassium — potash — is the fruiting nutrient: it encourages flowering, helps fruit swell and ripen, improves flavour and colour, and helps the wood harden before winter. That is why fruit feeds are usually high in potash and relatively low in nitrogen, and why tomato fertiliser, which is high in potash, is a good general feed for fruiting plants. Fruit also needs trace elements, especially iron, magnesium and boron, and a deficiency shows up as yellowing leaves or poor fruit set — but trace deficiencies are usually a sign of the wrong soil pH rather than a missing fertiliser, and fixing the pH is the real cure. The fertiliser calculator can help you work out how much to apply.
Compost and manure: the foundation feed
Well-rotted compost or manure, spread as a mulch in spring, is the best general feed for almost all fruit. Spread two to three inches over the root zone, keeping it away from the trunk, and let the worms and the rain carry it down. Compost feeds slowly all season, improves the soil structure, and holds moisture — three benefits no bagged fertiliser offers. Use well-rotted manure, not fresh manure, which can burn roots and carries weed seeds and pathogens. For berries, a spring mulch of compost is usually all the feeding they need in a year. For trees, compost plus a potash feed at fruit-swelling time is a complete programme for most gardens. Do not dig compost into the soil around established roots — spread it on the surface and let nature do the work. If your soil is poor or sandy, feed with compost twice a year, in spring and again in autumn.
When and how to feed each type of fruit
Feed fruit trees in early spring, just as growth starts, and again with a high-potash feed as the fruit begins to swell. Stop feeding by midsummer so new growth can harden before winter — late feeding is one of the commonest causes of winter damage. Raspberries and blackberries are hungry and benefit from a spring feed of compost plus a potash feed in early summer. Strawberries need feeding after the main crop, not before it: feed June-bearing strawberries after fruiting, and everbearing types lightly through the season. Blueberries need an acid fertiliser made for ericaceous plants, applied in spring, and they should never be given lime or ordinary fertiliser. Citrus is the hungriest fruit tree of all and needs feeding every two weeks through spring and summer with a citrus fertiliser. Grapes need very little feeding — too much nitrogen makes them grow leaves instead of fruit — and a spring mulch of compost is usually enough. Figs are similar: a light feed in spring, and little else.
Reading the plant: signs of too much and too little
A fruit tree tells you what it needs if you know what to look for. Pale yellow leaves and weak, thin growth usually mean nitrogen shortage, and a spring feed of compost or a balanced fertiliser will help. Leaves that yellow between green veins often mean iron deficiency, which in blueberries almost always means the soil is too alkaline rather than short of iron — check the pH before adding iron. Dark green, lush, soft growth with few flowers means too much nitrogen, and the cure is to stop feeding and let the tree settle. Small fruit that drops early can mean the tree is short of potash or water, or simply carrying too much fruit — thin the crop before blaming the feed. Brown leaf edges can mean potash shortage or salt damage from over-fertilising. If the symptoms do not fit a simple explanation, or if several plants are affected, the plant disease checker can help rule out disease, and your extension service can arrange a soil test.
Organic feeds and what they do
The organic feeds most useful for fruit are compost, well-rotted manure, seaweed meal or liquid seaweed, bone meal and wood ash. Seaweed is a good general tonic: it supplies trace elements and growth hormones, and a liquid seaweed feed every few weeks through the season suits berries and young trees. Bone meal supplies phosphorus and is useful at planting time, mixed into the bottom of the hole. Wood ash supplies potash and raises pH, so it suits apples and plums on acidic soil but must never be used on blueberries. Epsom salts supply magnesium and can help if a soil test shows a deficiency, but they are not a general tonic and should not be used routinely. Coffee grounds and eggshells are often recommended, but their effect is small and slow — they are better in the compost heap than spread directly. Whatever you use, follow the label rate: more is not better, and excess fertiliser washes into waterways and damages soil life.
Fertilising mistakes to avoid
The classic mistakes are feeding at the wrong time, feeding too much, and feeding the wrong plant. Feeding in late summer or autumn pushes soft growth that winter frost kills. Feeding a newly planted tree heavily can burn its roots — compost at planting is enough in year one. Feeding blueberries with lime or ordinary fertiliser raises the pH and turns the leaves yellow. Scattering fertiliser against the trunk can burn the bark; always spread it over the root zone, under the canopy edge, and water it in. And feeding will not fix a problem that is not nutritional: a tree that is short of water, planted in shade or diseased will not fruit better because you fed it. Fix the light, the water and the drainage first, and feed second.
Frequently asked questions
When should I fertilise a fruit tree?
In early spring as growth starts, with a high-potash feed as the fruit swells. Stop feeding by midsummer so new growth hardens before winter.
What is the best fertiliser for fruit trees?
A mulch of compost in spring plus a high-potash feed at fruit-swelling time suits most fruit. Tomato fertiliser works well as a potash feed, and citrus needs a citrus fertiliser.
Why are my fruit tree leaves yellow?
Pale yellow leaves can mean nitrogen shortage; yellowing between green veins often means iron deficiency caused by alkaline soil, especially in blueberries. Check the soil pH before adding fertiliser.
Can I use manure on fruit trees?
Yes, well-rotted manure as a spring mulch is excellent. Never use fresh manure, which can burn roots and carry pathogens, and keep it away from the trunk.
Should I fertilise blueberries like other fruit?
No. Blueberries need acidic soil and an ericaceous fertiliser, and they must never be given lime or ordinary fertiliser, which raises the pH and turns the leaves yellow.
Feed fruit like a good cook seasons food: modestly, at the right time, and with the right ingredient for the dish. Compost in spring, potash as the fruit swells, and nothing late in the season. For the feeding needs of individual fruits, see the growing guides, including apples and blueberries, and use the fertiliser calculator to work out rates.