Before a fruit tree can bear fruit its flowers need pollinating. Some trees, like 'Victoria' plum and 'Morello' and 'Stella' cherries, are self-fertile and set fruit with their own pollen. However, the majority are self-incompatible and need pollination from a different cultivar of the same fruit type that flowers at the same time. Even self-compatible cultivars set more fruit if cross-pollinated.
Pollination groups
Different cultivars flower at different times. This means a late-flowering cultivar won’t be open in time to pollinate an early-flowering one. To avoid such problems fruit cultivars are divided into groups, according to their flowering period. Choose a pollinating cultivar from the same group for preference, or one from the preceding or following group, as there is likely to be some overlap in the flowering period.
As an example, pollination group 2 apples often flower in late March and include ‘Beauty of Bath’ and ‘Egremont Russet’, while group 5 cultivars which flower later, include both ‘Newton Wonder’ and ‘Mother’.
Complications
Incompatibility groups:
Cultivars in these groups are self- and cross-incompatible.
This means they neither set fruit with their own pollen, or
with pollen from any other cultivar within the same Incompatibility
group.
e.g. Apples: 'Cox's Orange Pippin' & 'Kidd's Orange Red'
Pears: 'Laxton's Progress' & 'William's Bon Chrétien'
Plums: 'Jefferson' & 'Coe's Golden Drop'
Good nurseries will generally be able to advise on compatibility or refer to RHS Fruit and Vegetable Gardening, by Michael Pollock, Dorling Kindersley, 2008, ISBN 9781405331265.
Triploid cultivars:
Most fruit cultivars are diploid and need only one other cultivar
as a pollinator. Triploids (three sets of genes), however, require two diploid cultivars
to cross-pollinate them - and each other as triploid's are sterile.
e.g. Apples: 'Bramley's Seedling', 'Jupiter'
Biennial bearing:
Some fruit cultivars flower well one year, but not the next.
In the poorer year fewer flowers are produced so effectiveness
as a pollinator is reduced.
e.g. Apples: 'Blenheim Orange', 'Laxton's Superb'
Limited space
Neighbouring pollinators must no more than 18m (60ft) away from each other. ‘Family’ trees are available, where up to four compatible pollinators are grafted onto one tree. Alternatively, see if your neighbours have a fruit tree and select a compatible cultivar or suspend a few flowering branches of a suitable pollinator from a neighbour’s garden, in the tree.
Pollination and pesticides
The transfer of pollen from one flower to another is largely carried out by bees. These include the honeybee, bumble bees and many species of solitary bees. Avoid applying a pesticide while fruit trees are in flower as most insecticides are dangerous to bees. Where fruits trees are being grown in grass, mow the grass before an insecticide is applied to remove dandelions and other bee-attractive flowers growing near the trees. Some fruit, for example peach and nectarine, flower in early spring when few bees are active. For these it is helpful to hand pollinate the flowers with the aid of a soft artist’s brush. This also applies to fruits being grown in conservatories.