Fruit Tree Rootstocks

Fruit Rootstocks

As many gardeners will know, fruit trees are very seldom grown from cuttings or from seeds or pips. The reason for this neglect of the apparently obvious and cheapest way of growing trees is really quite straightforward.

Almost all tree fruits are of a specific variety; each is quite distinct from all others. This is the way we buy the trees and also the fruit. Unfortunately, seeds and pips from most tree fruit like apples, pears, plums and berries, will not come true to type. That is to say, trees raised from seeds will be unlike ether parent; so will the fruit. Clearly, this is useless state of affairs and it means that all named varieties have to be propagated vegetatively if you want to produce identical offspring.

The easiest way of doing this is from cuttings but, and here’s the snag, most fruit trees are very difficult to root as cuttings. Nursery owners are, therefore, clearly not going to waste time, labour and space and tend to use another method.

The methods that are virtually 100 per cent successful are budding and grafting. Both involve planting a ready-made set of roots, called the rootstock, and then binding a piece of the required tree onto it.

'T' budding

With budding, a single bud of the wanted variety is inserted under the bark of the rootstock in July and, within a year a small tree has grown from the introduced bud.

Grafting uses the same principle, but is carried out in spring with a short length of shoot instead of a single bud. The rootstock is cut to a few inches high and the length of shoot is joined to it in a special way. Once again, a bud grows out to form a new tree.

Whip and Tongue Grafting

There is, though, a reason other than ease of propagation for using a rootstock. Originally, rootstocks were seedlings because they could be raised cheaply and it didn’t matter if their characteristics varied because they were only wanted for their roots.

However; it was then realised that the rootstocks imparted certain features to the trees that were then grown on them. For instance, a vigorous and strongly growing rootstock gave rise to a similarly behaved tree, while a weak rootstock gave a small tree. This was, and still is, the most important feature of this method of propagation. It enables one to raise any number of identical fruit trees of a known and predetermined character.

The very fact that apples form by far the largest slice of the commercial fruit acreage means that more research has gone into growing them than other fruits. This has led to a wide range of different rootstocks for apples.

Obviously, we as gardeners are going to benefit from all the development work as well, but, luckily, our standard of growing doesn’t have to be as high as that of commercial growers. For that reason, the number of different rootstocks used by nurserymen when raising trees for amateurs is mercifully small.

 

Apple Rootstocks

Rootstocks are always described with reference to the vigour. There are three in common use for sale in garden centres.

M9 is normally the most dwarfing one and is useful where a small tree is wanted. These, though, need the support of a stake throughout their life as the root system is small and far from robust. Trees on M9 need good soil if they are to give of their best. It is used for intensive tree forms like cordons, dwarf pyramids and, sometimes, bush trees.

M26 has slightly more vigour and is suitable for small trees on poor soils. Trees should be staked after planting and may need to be always. M26 does not suit all varieties and soils so advice from the nurseryman should be sought. Suitable tree forms are the same as above, with the addition of espaliers.

The most widely used apple rootstock is without a doubt MM106. It is described as semi-dwarfing and is suitable for all garden tree forms and sizes. The only time that it would be inappropriate is for small trees on good soil, when M26 or M9 would be better.

Another rootstock, M27, has appeared on the scene recently. This is very dwarfing and is not normally suitable for gardens unless you are an experienced gardener and know your soil.

 

Pear Rootstocks

Pear trees are not grown on pear rootstocks but on quince. The choice is limited to Quince A and Quince C. Quince C, however, has had a chequered history and is seldom used now.

Quince A is by far the more common and is certainly the one used by most nurserymen. It produces quite a large tree, but one that is perfectly satisfactory for most gardens and uses.

 

Plum Rootstocks

Here again, the choice is really between two: the much more common and rather vigorous St Julien A and the newer and smaller Pixy.

Pixy is seldom used now; it had a short and inglorious life because the tree size is not significantly smaller than those on St Julien A, whereas the fruits are. Some nurseries still use it for raising a fewVictoria plum trees, but it has little to commend it and nurserymen are unwilling to take up space with another unnecessary rootstock.

St Julien A (but not Pixy) is also used for peaches, nectarines and apricots.

 

Other Rootstocks

With the arrival of the new and semi-vigorous Colt rootstock, cherries came within the grasp of more home gardeners. However, they are not sufficiently dwarfing to allow cherries to be grown in small gardens.

The main dwarfing rootstocks for this are Gisela 5 and 6. Both are derived from Prunus cerasus x P canescens. These two rootstocks are not only dwarfing, but they are also far less susceptible to the two main cherry viruses. They do, though, get phytophthora root rot on wet land.

14. May 2011 by admin
Categories: Fruit Gardening, Fruit Trees | Tags: , , | Leave a comment

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