Size Controlling Rootstocks

Apple varieties do not grow true to type from seed. A seed from a McIntosh apple will not grow in to a McIntosh tree. As a result, apple trees are propagated by grafting or budding the desired variety onto a suitable rootstock. Thus apple trees are composed of two parts, namely rootstock and scion variety.

Originally apple trees were grafted onto seedling rootstocks resulting in a tree 25 ft tall and 30 ft wide (7.6m - 9.1m). These were called standard trees. In the 1960’s, semi-standard rootstocks were used resulting in trees about 18 feet x 20 feet (5.5m - 6m).

In the 1980’s semi-dwarf rootstocks came in giving trees 12ft tall and 15 ft wide (3.6m - 4.5m). In the 1990’s fully dwarfing rootstocks have become popular, resulting in trees 8 ft tall x 10 ft wide, or smaller (2.4 - 3m).

Some rootstocks can result in apple trees 6 ft tall x 6 ft wide (1.8m -1.8m). Home gardeners may not have much choice in the size of apple trees that they can buy. Commercial orchardists want small trees and the nurseries are obliged to provide these. Typical dwarfing rootstocks are M26, M9, M27, B9 and 03.

*Note - All apple trees on dwarf rootstock will require support. The trees are very small with thin wood. The fruit produced is of normal size. A full crop of apples on a small tree is a heavy weight to support. Branches can break off. The root system is shallow and trees may fall over.

The most common form of support is to pound a 2 inch diameter post (5cm) into the ground beside the tree. The trunk and branches are tied to this support post. Various trellis systems can also be built.

Planting

Planting distances will depend on the rootstock being used. Choose nursery stock that is suited to the space available. Select a well grown one or two year old tree from the nursery. Two year old apple trees should have at least four or five well spaced branches with a good root system.

Dwarf apple trees should have many branches (feathers). The usual practice is to plant early in the spring but planting can be completed in the fall when weather conditions are good and the soil is moist.

Prepare a hole slightly larger than the root spread. Trim off any injured or broken roots before planting. If the tree is in a plastic pot, remove the pot. If the tree is in a fiber pot, you can slit the sides of the pot and plant with the pot-or remove the pot.

Sprinkle a handful of bone meal in the bottom of the hole (phosphorus) to help the root system get established quickly. Place the tree in the hole, mix in some peat moss or compost with the planting soil. Replace the soil in the hole, treading the soil firmly around the roots to ensure that the tree is firmly anchored. Give the tree a good watering.

*Make sure on dwarf apple trees that the graft union remains 2 to 3 inches (5cm - 8cm) above the permanent soil level. If soil is piled up over the graft union, scion rooting may occur and the dwarfing effect will be lost.

Pruning

Dwarf apple trees are normally grown to a central leader system. At planting time, if there are no side branches, cut the tree back to 32"-34"(81-86 cm) above the ground. If the tree has lots of side branches (feathers) cut the leader back to 8" (20 cm) above the top branch. Remove any branches closer to the ground than 20" (50 cm).

Aim to develop a framework of well spaced branches that are capable of bearing crops without breaking. In subsequent years, switch from heading to thinning cuts. Cut out entire shoots that are crowded or crossing into the centre of the tree. Narrow angled crotches should be avoided as these are sources of weaknesses. As the tree starts to bear fruit, prune for convenience in picking, spraying, and to allow light to enter all parts of the tree.

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