Apples - Avoiding Biennial Bearing
Some apple trees bear heavily one year and sparsely the next. This is called biennial bearing. A very heavy crop one year may prevent adequate bud formation for the following year.
Varieties which are expecially prone are Blenheim Orange, Bramley, Claygate Permain, Tom Putt, Devonshire Quarrenden, Early Victoria, Wyken Pippin, Ellison's Orange, Elstar, Laxton's Superb, Laxton's Fortune, Rev. W. Wilks, Tydeman's late orange.
Preventing biennial bearing on some trees is difficult. There's also the problem that a group of trees will often become biennial together.
The remedy, which sometimes works, is to thin. Authorities differ as to how and when.
"Early, heavy thinning during the large-yield year. Thin fruit to between 9" apart and 5" apart depending on size, within 30 days of the petals coming off".
"Do it early, soon after fruit-set. Don't wait for the June Drop. Thin fruit to between 3" and 5" apart".
"Thin leaving a single apple every 6 to 8 inches - this will double the percentage of large fruit".
Some growers suggest rubbing out some of the fruit buds in the heavy-cropping year.
Joan Morgan and Alison Richards ( who wrote "The Book of Apples") recommend thinning when the apples are just under half an inch across. Eaters to 4 - 6 inches apart; cookers a bit further apart. "Pinch out the fruitlets as soon as possible after the fruit has set."
When a tree starts going biennial some of the buds look odd in the "off" year. I've taken photographs to illustrate this. These swollen
buds send out two or three wood shoots rather than
blossom. These buds plus their shoots have to be
cut off; they contribute nothing useful to the tree.
Nigel Deacon / Diversity website
