Dwarfing Rootstocks for Fruit Trees

Fruit and nut trees are a long-term investment in the home orchard. Gardeners selecting fruit trees need to make wise decisions concerning varieties, rootstocks, pollination requirements, planting distances, staking and trellising requirements, hardiness and season of maturity. In addition, fruit taste and how the fruit will dry, freeze, can or store is very important. It is also important to consider the growing conditions available in your garden.

One problem with growing fruit trees in a backyard situation is simply lack of space. Large fruit trees take a great deal of room that many back yards lack. Another consideration is the time it takes fruit trees to come into production. Since the average American moves every seven years, that becomes important.

You can tell when moving time has come because you have finally started to pick some fruit from the trees that you planted when you moved in. We often are unable to harvest fruit from our trees because it takes so long for them to start producing.

In an attempt to produce earlier and larger fruit crops, a great deal of work has gone into selecting dwarfing rootstocks. In general, you can select from dwarf, semi-dwarf or full-size trees. This tree-size rating is important because it enables us to select rootstocks that will produce smaller trees. Smaller trees are easier to prune, spray and harvest. They also start producing fruit much sooner than a standard type tree.

Dwarf fruit trees are created by combining several different trees. The fruiting part of the tree is called scion variety. It is dwarfed by the rootstock or interstem. These rootstocks or interstems produce a small tree with full-size fruit. In addition, there are some true genetic dwarf trees, in which the entire tree is dwarfed. Unfortunately the variety selection in these genetic dwarfs is very limited.

If we are trying to select a satisfactory dwarfing rootstock, we need to understand a little bit about the designation of Malling (M) or Merton-Malling (MM), which are rootstocks. These rootstocks were collected and standardized by experiment stations in Great Britain so growers would have an indication of tree size.

The chart on this page shows the percentage of dwarfing available on different rootstocks. Standard trees are full-size trees; Malling 7a trees are about 40 percent of standard tree size; and Malling 27 are only about 25 percent standard tree size. As you select trees, select them not only on the basis of size but on the basis of what the rootstock is going to do in our area. In general, we recommend the Malling 7a for heavier soils. Malling 7a is resistant to some root diseases and will produce a tree about 15 to 18 feet tall.

A tree with a Malling 7a root makes a semidwarf tree. This is an excellent choice for a backyard orchard. Unfortunately, good dwarfing rootstocks are only available for apples. Pears are often grafted onto quince rootstocks, but these often become sickly and die in hot weather.

All of the stone fruits lack a good dwarfing rootstock. Many trees are sold on dwarfing rootstocks, but about 50 percent of these will develop graft incompatibility problems and will eventually die. Stone fruits, with the exception of cherries, can be kept within the bounds of most backyard gardens by proper training and pruning.

In addition to the rootstock, many other things affect the size and productivity of your trees. Of course, training and pruning have a major effect on this. Two dimensional trees, that is, trees grown by an espalier method, are often very satisfactory in backyard orchards.

If you are going to add to your home orchard this year, start thinking of those selections. First, do you have the space needed for those trees? Fruit trees do not do well growing in full shade nor under the canopy of large shade trees. They will not tolerate wet soils and should not be planted in flower beds or lawns because of their different watering requirements.

You may have to shop around to get the combination of varieties as well as root stocks that you want. Many local nurseries will be getting their fruit trees in shortly. If you are looking for a special variety, get there early, as many of the choice varieties are often sold out quickly.

Bare-root trees work very well, provided they are planted and cared for properly early in the season. If you do have a favorite old variety of fruit tree, gather some scion wood right now. Cut 12- to 18-inch lengths of vigorous twigs that grew last year. Select twigs that are slightly larger than a pencil.

Wrap them in some moist toweling and put them in a plastic bag and store them in the vegetable bin of your refrigerator. Grafting and budding cannot be done for several weeks, but you must have dormant scion buds to do the propagating.

Written by:

Larry A. Sagers Extension Horticulture Specialist Utah State University Thanksgiving Point Office