Encouraging successful pollination
To successfully produce fruit, the flowers need pollinating. This is usually done by flying insects like honey bees, bumblebees, flies, beetles and wasps.
Whereas most soft fruit produce compatible flowers and pollen and are therefore self-fertile, many fruit trees have self-incompatible flowers, meaning that they need another different cultivar of the same fruit that flowers at the same time growing nearby to pollinate their flowers.
If you live in a built-up area there are likely to be other fruit trees growing in close proximity, so there may be adequate pollination nearby and just the one tree will be enough in your garden. Although pollinating bees can travel 3–4km (1–2miles), the general rule of thumb is that trees for cross-pollination should be within 18m (55ft) of each other to be really effective.
Some fruit trees, such as ‘Victoria’ plums and ‘Stella’ cherries are self-fertile, so that insects pollinating their own flowers will lead to successful fruit set. This is ideal in a small garden as only one tree is needed to produce fruit. However, even self-fertile varieties tend to crop better when another cultivar is planted nearby for pollination.
As flowering time is critical, fruit trees are classified into various flowering groups, so that it is easy to choose cultivars that will flower at the same time and effect pollination.
To complicate things further, a few apple and pear cultivars (known as triploids) such as ‘Bramley’s Seedling’, ‘Holstein’, ‘Ribston Pippin’, ‘Blenheim Orange’ and ‘Catillac’ produce mainly sterile pollen. These won’t be any use for cross-pollinating other trees, and still need other trees to set their fruit. Therefore if you grow a triploid cultivar you will also need two other trees that will pollinate each other as well as the triploid, and these three cultivars must all flower at the same time.
Crab apples are particularly useful for pollinating apples as they produce an abundance of flowers over a long period.