Apples are perfectly hardy in this country, but given the protection of a wall some of the finest varieties, such as ‘Cox’s Orange Pippin’, will succeed in the north of England when they would not do so in the open garden. Apples make very pretty wall trees everywhere, in fact, with their blossom in spring and their ripening fruit in summer through to the autumn. They are best trained as vertical or diagonal cordons, or as espaliers, with the branches in horizontal tiers on each side of the trunk. Diagonal cordons grow about 3m (10 ft) long, and occupy 2.1 m (7 ft) of wall height. An espalier will grow about 2.4m (8 ft) tall, and 3.0-3.6m (10- 12 ft) across. Some varieties, such as ‘Bramley’s Seedling’, are too vigorous for the tight training of the cordon or espalier, but responsible nurserymen do not supply this type of tree in an unsuitable variety.
All apples crop better if there is another variety nearby as a pollinator, and no commercial grower would dream of planting an orchard with only one variety for that reason. Gardeners usually have neighbours who are growing apples, and there is generally enough pollen from different trees being carried about by bees and other insects to cross-everybody’s apples, except the most self-sterile varieties. Unfortunately, the most popular English apple, ‘Cox’s Orange Pippin’, is one of the difficult ones, being almost completely self-sterile, so if you want to be sure of a good crop, you should plant a pollinator nearby – try ‘James Grieve’ or ‘Worcester Pearmain’.
General care: Apples like a deep, fertile soil, well drained but kept moist. For this reason, avoid a hot, sunny wall which might dry out in the summer. Before planting, set up the training wires on the wall. For cordons, set horizontal wires 90 cm (3 ft) and 1.8m (6 ft) from the ground, with canes stuck into the ground and fixed to the wires, diagonally or vertically. Cordons are usually grown diagonally because they need less wall height that way, and because they fruit better. The height and number of horizontal wires for espaliers depend on how many tiers of branches you want to grow, and what distance apart they are, but five or six tiers each 37.5 cm (15 inches) apart is usual.
Buy partly trained trees, two or three years old, and plant any time in the winter, but as early as possible. Single cordons are planted 60 cm (2 ft) apart. Each winter, reduce the extension growth which the tree has made that year by a half, to encourage laterals. Tie the tree to the cane as it goes up it. When it gets to the top, cut back to a lateral which is pointing upwards and carry on as before. When the cordon is established, cut back all the long laterals each winter to within a couple of buds of the base. Espaliers are usually started off by the nurseryman, but there is no reason why you should not go on adding a tier a year until you get to the top of your wall.
In spring, select three good buds at the top of the tree and remove the rest. The middle one will form the extension shoot, and the other two branches either side of the main trunk. In the summer, fix the side branches to grow at about 45°, and in the winter carefully bring them down to the horizontal, tie them to the wire, and start to make the next tier. When the espalier is established it is pruned as if it were a number of horizontal cordons.
After the June/July natural drop of fruit, apples should be thinned to 10 cm (4 inches) apart. Give anmulch of or well-rotted farmyard manure, and water in a dry summer, especially for young plants. Apples have a high requirement of potassium, and should be given 15g per tree of sulphate of potash annually to maintain fruit quality once the tree starts cropping. Give nitrogen in the form of 30g (1 oz) of sulphate of ammonia per tree annually from planting time, but cut this down if the tree makes too much vegetation. Give phosphate in the form of superphosphate – 15g (1/2oz) per tree annually.
Propagation: Apples are budded or grafted commercially on to one of a range of specially bred rootstocks.
Pests and diseases: Birds eat the flower buds, and peck holes in the fruit. Try strands of cotton strung between the branches, or nets. Apple saw-fly and codling moth caterpillars burrow into and eat the fruit. Spray with fenitrothion at petal-fall, then again one month later, and again three weeks after that. A tar oil wash every winter will control many pests.
Three fungal diseases can be controlled by spraying with benomyl: apple canker, which attacks the bark; apple, which affects the young shoots; and apple scab, which affects the fruit.
Fire-blight, a notifiable bacterial disease, causes a blackening and shrivelling ofand and dieback of branches. There is no effective treatment. Affected branches must be cut away well below the infection and burned. Brown-orange spots on the indicate that the tree is not getting enough magnesium. Spray or water the whole tree with Epsom salts.