Biennial bearing is a problem in some fruit trees, particularly apples and pears, where they crop heavily in one year and then produce little or nothing the next. Some cultivars are naturally biennial but weather conditions and soil fertility can contribute to the problem.
What is biennial bearing?
Biennial bearing occurs in fruit trees where they carry a heavy crop one year and little or none the next. Without a crop to support in any one year, trees use their resources to produce flower buds leading to tremendous blossom the following year. The resulting heavy crop reduces the tree’s resources so that little blossom is made the following year.
This is a common disorder with apples and pears but can occur with a range of tree fruits.
Some apple cultivars, are prone to biennial bearing including ‘Blenheim Orange’, ‘Bramley’s Seedling’ and ‘Laxton’s Superb’ but almost any apple or pear can fall into this pattern of cropping.
It is most likely to be initiated where trees are starved or receive insufficient moisture. This makes them unable to carry a heavy crop which in turn stimulates the production of excessive flower buds for the following year.
Biennial bearing can also be started by frost destroying the blossom one spring.
Once a tree is into a pattern of biennial bearing it can be difficult to correct. Try the following:
Thinning fruit buds
Firstly, identify your fruit buds. Then, in early spring before an expected heavy crop year, rub off half to three-quarters of the fruit buds, leaving just one or two per spur. Simply rub them off the branch with your thumb and forefinger.
Alternatively, select half the branches in any one year, mark them and remove all the fruit buds on them. Do the other non-marked half the following year.
Another method is to, a week or ten days after the flowers open, use scissors or pinch out each blossom at the stem, taking care not to damage the leaves below.
The aim with thinning flower buds is to encourage the tree to produce a moderate crop, leaving enough resources for the formation of fruit buds for the following year.
Thinning fruits, however early it is done, is much less effective than thinning the fruit buds in early spring. However it has the benefit of increasing the average size of remaining fruits, and is often done for this reason alone.
Watering and feeding
Ensure trees are receiving adequate moisture by clearing away competing grass and weeds from around the base of the tree over a radius of 1m (3½ft). Small trees should also be mulched with compost or well-rotted manure to a depth of 5-8cm (2-3in) over the cleared area.
In dry spells water well applying 20 litres per square metre (4½ gallons per square yard) over the entire root area every 10 days.
Feed in early spring, applying 100g of general purpose fertiliser per square metre (3oz per square yard).