Why thinning is the best thing you can do for your apples

Left to its own devices, an apple tree sets far more fruit than it can ever bring to a decent size. A mature tree might carry a thousand fruitlets in June and have the resources to swell perhaps two hundred of them properly. The rest stay small, hard and sour, or drop before they ripen. Thinning is the gardener's way of making that decision on the tree's behalf, and it is the single most effective thing you can do between now and harvest.

It is not only about size, though size is the reward you notice first. Removing the surplus:

• Lets the remaining apples grow larger, colour better and develop more sugar and aroma.
• Eases the strain on the tree, which helps break the cycle of biennial cropping — a heavy crop one year, almost nothing the next.
• Opens up the canopy so air and light reach the fruit, which means less scab and less brown rot.
• Stops apples touching each other, denying wasps, codling moth and fungal spores the dark, damp corners they love.
• Takes weight off the limbs, so branches are far less likely to snap under a summer storm.

When to thin

Apple trees do some of this work themselves. About four to six weeks after petal fall, usually in late June or early July, they shed a proportion of their fruitlets in what is known as the June drop. It looks alarming, but it is simply the tree balancing its books. Do not panic and do not rush out with the secateurs beforehand — you would be thinning twice over.

Wait until the drop has finished, then thin when the fruitlets are roughly the size of a walnut, about 2–3cm across. In most UK gardens that means late June through mid-July, a little later in the north or after a cold spring. Choose a dry, overcast day rather than a baking afternoon; the tree is under less stress, and you are less likely to knock off fruit you meant to keep.

How much to leave

The aim is one or two fruits per cluster, with clear air between them. In practice, work to a spacing along the branch:

• Dessert apples: leave one fruit every 10–15cm.
• Large culinary varieties such as Bramley or Howgate Wonder: 15–20cm, because each apple will be genuinely big.
• Cider and small-fruited varieties: 8–10cm is often enough. Bittersweet and bittersharp cider apples are usually thinned more lightly than dessert fruit — you want volume for the press, but the fruit still needs room to ripen evenly.

When you look at a cluster, you will see a central fruit, the king fruit, with smaller ones around it. The king is often the biggest, but it is also the most likely to be misshapen. Take it out along with the runts, any fruit with blemishes or maggot holes, and anything growing in a tight corner against a branch. What you leave should be a well-shaped, unblemished lateral fruit with room to swell.

The technique, and how not to damage the tree

Use your thumb and forefinger to grip the fruit and twist it gently sideways until the stalk snaps cleanly. Do not pull downwards — that is how spurs, the short stubby shoots that carry next year's blossom, get torn off. If a stalk is stubborn, a pair of small snips is fine, but leave the spur intact whatever you do.

• Work from the top of the tree downwards and from the inside outwards, so you are not fighting branches you have already cleared.
• Support the branch with your free hand while you work; it steadies you and saves bark.
• Thin the whole tree in one pass, then walk round and check your spacing. It is easy to be timid at the start and ruthless by the end.
• Wear gloves. Apple spurs are sharp, and the sap makes your hands sticky within minutes.

Varieties that need it most — and a word for cider makers

Some trees thin themselves reasonably well; others need firm handling. The classic biennial bearers — Bramley, Discovery, Katy, Egremont Russet — repay thinning generously, because a lighter crop this year means blossom next year. Tip-bearing varieties can be thinned a little more cautiously, as you may be removing fruit from the wood that would have cropped next season anyway.

If you make cider in small batches, thinning earns its keep twice over. Evenly spaced fruit ripens together, so you can press a single variety at its peak instead of sorting through a mix of ripe, unripe and half-rotted apples. Cleaner fruit means less spoilage in the fermentation, and larger apples give more juice for the same amount of picking and milling. Thinning is, in a very real sense, the first step of the cider season.

Afterwards: use the thinnings, then keep an eye out

Do not leave the thinnings lying under the tree — rotting fruit attracts wasps and harbours brown rot spores. Compost them, feed them to the chickens, or use them while still green and hard: unripe apples are high in pectin and make excellent setting agent for jam, and they add a sharp note to a chutney.

Give the tree a good soak if the weather turns dry, top up the mulch, and go back a fortnight later. If clusters still look crowded, take a second, lighter pass — a few minutes now saves a great deal of disappointment at picking time.