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Tree Size

We receive many requests about tree size, and how it can be controlled. Tree size is also an important factor when choosing trees to plant in a mini-orchard, a garden, or in a pot on the patio. On this page we provide some general background information on tree size, and some guidance on choosing the right type of tree in your “orchard pack.”

It is mistaken to think that tree size can be controlled by pruning. The fundamental factor involved in determining tree size is the rootstock. Most fruit trees consist of two parts. The first is the “rootstock” or “stock,” which comprises the root system and the lower part of the stem, normally from soil level (the so-called “nursery mark”) to about 15 cm above the ground. The second is the “scion” which comprises the rest of the stem and the branches, and so it is this part that bears the fruit. Trees are created by grafting a tree variety – say Cox apple or Victoria plum – onto a rootstock, usually when scion and rootstock have a stem diameter of 8-10 mm.

This system is adopted to control the size of the tree and to improve cropping. So, for example, for apples, the rootstock named MM106 gives rise to a tree reaching a height of about 12 feet, while M26, M9 and M27 produce progressively smaller trees. M27 and M9 are therefore known as “dwarfing rootstocks.” The effect of rootstock is very marked on apples, less so on plums and pears. Another fact to remember is that the size of a tree at the time of planting does not affect the size eventually achieved. Likewise, the height of the tree at the time of planting has no effect on when the tree comes into production.

Other factors are involved in determining the height of a tree at maturity. These include type of soil, height of the location above sea level, exposure to cold winds or frost pockets, and the winter rest level of water in the soil. Equally important is tree spacing. The further trees are spaced apart, the greater their final height will be.
To help you planning your mini-orchard, here are some recommended planting distances, with a very approximate guide figure for final tree height (say 5 years after planting), for different fruit varieties:

You may ask, why can’t we be specific about planting distance? Why 8-12 feet and not, say, 10 feet? This is due to the many factors involved. Apart from the rootstock used, the variety of fruit, the depth of the soil, the available light and moisture throughout the growing season, all will influence the crop load and therefore the size of the tree. A heavy cropping tree will put on less new growth (extension growth) compared with a light-cropping tree. As an example of variety difference, Bramley’s Seedling makes a larger tree than, say, James Grieve. Trees grown on deep, water-retentive soil become larger than trees on drier or shallow soils. Trees grown in the shade crop less, and so tend to get larger than trees growing in sunshine. Fruit trees which go short of moisture during the summer months stop growing earlier each year, and will make shorter shoot extension growth. Fruit trees which are poorly pollinated will produce less fruit and therefore the annual extension growth will be much greater.

Finally there is the influence of the tree’s overall health, the site, microclimate, grass, weeds around the tree, depth of planting, nutrition, type of pruning, and the season in which pruning is performed. In fact, late summer pruning (in late July and August) tends to reduce the rate at which a tree will grow, whereas traditional winter pruning (November-March) produces strong regrowth of long new shoots.

So it’s a complicated equation, but it is one for which we are always available to give guidance and advice when you are ordering your orchard pack.

One rule of thumb that always applies is: if you have room, give the trees as much space as possible, so at the top end of the space range as detailed above. This gives them the chance to develop a fine tree canopy.

Let’s return to apples for a moment, because this is the fruit for which there are most rootstocks. We can safely say that MM106 is by far the best and most robust stock for a mini-orchard, and so they are the best choice for inclusion in our Standard Orchard Pack and Multi-fruit orchard pack. In addition, MM106 is suitable for all soils. At the other end of the scale, the dwarfing stock M27 is suitable for growing in a pot on the patio. If you have limited space, you may prefer one of the dwarfing varieties, but it is important to remember that M26, M9 and M27 require lots of attention, and water in the summer. M27 in particular is good for a patio or pot, but it has to be watered twice a week in summer. M26 and M9 are good for small gardens with limited space. They need a stake throughout the life of the trees, and extra water in summer.

For successful apple tree growing, then, MM106 is the best choice. It has proved itself over many years; it forms a healthy tree which fruits at a young age. MM106 is suitable for all soils, including heavy clay soils, provided the soil is not waterlogged.