Why one bumper year so often follows another

If your apple tree gave you a wheelbarrow-load last autumn and barely a dozen fruits this time round, you have met biennial cropping. It is not bad luck and it is not a disease. It is simply the tree's way of balancing the books. A heavy crop drains the tree of carbohydrates and nutrients during the very weeks when it should be busy forming flower buds for the following spring. Those buds are laid down in midsummer, so a tree carrying too much fruit in July effectively talks itself out of a crop next year. The result is the familiar rhythm: a glut, a famine, a glut.

The good news is that this is one of the few problems in the garden you can fix with your own two hands in a single afternoon. Thinning — removing crowded fruitlets in early summer — breaks the cycle and gives you a steadier, more useful harvest year after year.

Timing: catch them just after the June drop

Most apple trees shed a proportion of their fruitlets naturally in early summer, a process gardeners call the June drop. It is the tree's own attempt at thinning, and it usually is not nearly enough. Wait until that drop has finished, then step in.

In most of the UK that means late June to mid-July, when the remaining fruitlets are roughly the size of a marble or a small walnut, about 20–25mm across. This window matters more than many gardeners realise. Thinning later than mid-July may still improve the size of this year's fruit, but it comes too late to influence whether the tree sets buds for next year — which is the whole point of the exercise.

If you can only manage one pass, do it then. If you have the time, a second look in early August lets you tidy up any clusters you missed.

How much to take off

The first time you thin properly, it will feel brutal. You are removing perhaps 80 to 90 per cent of the fruitlets on a heavily laden tree, and every instinct will tell you to stop. Trust the process. A tree left to its own devices will produce a great heap of small, knobbly apples; a thinned tree produces fewer fruits that are noticeably larger, better coloured, sweeter and far less prone to rot.

• Dessert apples: leave one fruit roughly every 10–15cm along the branch — about a handspan apart.
• Culinary apples: aim for 15–20cm, since these growers are expected to swell to a good size for cooking.
• Clusters: reduce each cluster to a single fruit. Two or three apples pressed together will rub, bruise and rot.
• Young trees: be especially ruthless. Letting a two or three-year-old tree carry a heavy crop can check its growth for years.

A useful sanity check is to glance along a branch you have finished. You should still see a scattering of fruit, evenly spaced, rather than a string of beads.

Choosing which fruitlets to keep

Once you know how many to leave, the question becomes which ones. Work through each cluster and keep the best-shaped, cleanest, healthiest-looking fruit. Remove the rest.

Many growers deliberately take off the central "king" fruit of each cluster. It is often the largest, but because it sits in the middle it can be misshapen from uneven pollination. The smaller side fruitlets are frequently better proportioned. Take out anything that shows:

• Codling moth holes or the telltale frass at the eye
• Ribbon-like scars from apple sawfly
• Frost marking, russeting or scabby patches
• Distorted, lopsided or undersized growth

Removing damaged fruit early also prevents problems spreading. Rot, in particular, travels quickly between apples that are touching, and a single brown, mummified fruit can spoil the ones around it.

The technique, and doing it kindly

Use your thumb and forefinger to twist the fruitlet gently until it parts from the spur. A sharp pull can tear the spur and damage next year's bud, so ease rather than yank. Where clusters are tight, small garden snips or even nail scissors let you cut the stalk cleanly without disturbing the neighbours. Snips are also easier on the hands if you have a lot of trees.

Work from the top of the tree downwards and from the inside outwards, so you are not fighting your way through branches. Use a stable step ladder and never overreach — a fall from a ladder in July is a far more serious business than an imperfectly thinned tree. If you have a large, unpruned old tree, do not despair at the scale of the job. Thinning even the lower branches and the fruit you can comfortably reach makes a real difference, and partial thinning is infinitely better than none.

Drop the thinned fruitlets into a bucket rather than leaving them on the ground. Take them to the green waste collection or put them in the bin, not on the compost heap, as this helps break the life cycle of codling moth and sawfly.

Other fruits that repay thinning

Apples are the classic case, but the same principle applies elsewhere on the plot.

• Pears: thin clusters to a single fruit, spaced about 10–12cm apart.
• Plums: notorious for overcropping and snapping branches under the weight. Thin to 5–8cm, and you will get larger fruit and a healthier tree.
• Cherries: 5–8cm spacing suits both sweet and acid types.
• Trained apples and pears: cordons, espaliers and fans are less prone to biennial bearing, but thinning still improves fruit size on heavily set spurs.

Keeping the tree in balance afterwards

Thinning is the main lever, but it works best alongside sensible aftercare. Water young and heavily cropping trees during dry spells, particularly while the fruit is swelling in July and August. Mulch in spring to hold moisture, and avoid heavy nitrogen feeding, which pushes leafy growth at the expense of fruit and flower buds. A balanced feed in late winter suits most garden trees, and a light dressing of sulphate of potash in spring helps fruit quality.

Do it once, do it properly, and you will notice the change within a season or two: less of a glut, no barren year, and apples that fill your hand rather than your pocket.