Advice
RHS Help & Advice
Biennial bearing
Biennial bearing occurs when apples have 'on' years, with abundant crops, and 'off' years when little is gathered. Some apples, 'Laxton's Superb' and 'Beauty of Bath' for example, do this naturally, while others are tipped into this mode by a frosty spring for example, when no blossom is pollinated.
Without a crop to support, the trees use their resources to produce flower buds leading to tremendous blossom the following year. The resulting heavy crop reduces the trees resources, so that little blossom is made for the following year.
It appears that flower initiation for the following year occurs when shoot growth is finished and leaves are mature. The seeds within developing fruit seem to inhibit flower bud initiation, and most of the inhibition takes place in the first few weeks after pollination.
Sometimes poor pruning, where insufficient new growth is encouraged and too much older flower-bearing wood is retained, can cause this.
Thinning the blossom, removing nine out of 10 flower clusters, without removing any foliage, can help. With big trees only some branches need to be treated. However permanently modifying cropping patterns from biennial to annual bearing might take several years of blossom thinning.
Thinning fruits, however early it is done, is much less effective than thinning blossom at preventing biennial bearing.