Fruit tree height calculator
Try out our fruit tree height calculator here.
Almost all fruit trees are produced in fruit tree nurseries by grafting the desired scion variety (e.g. Braeburn apples or Victoria plums) on to a rootstock. The rootstock has a number of characteristics but the most important is that it controls the size of the mature tree.
Many fruit tree text books have a table showing you the likely size of the mature tree on different rootstocks. For example in the case of apples, sizes go from M27 – which limits the height of the tree to around 2m – to M25 – which produces a tree with a mature height of 6m or so. The implication is that the rootstock is the only factor affecting the final size of the tree.
However in practice it is not as simple as that, and the size is strongly influenced by two other factors: the quality of the soil, and the natural vigour of the scion variety. Trees growing on poor soils will not be as big as the same variety on the same rootstock growing on better soil. Similarly a Bramley’s Seedling apple tree growing in the same soil and on the same rootstock as a Cox’s Orange Pippin is always going to produce a much bigger tree, because of the inherent vigour of this variety.
One of our contributors, N. Buck, has produced a formula linking rootstock, soil quality, and the natural vigour of the fruit tree variety. This method potentially gives a more accurate prediction of the likely mature height of a fruit tree.
Assessing soil quality
The calculator ranks soil quality on a 5-point scale:
- Poor
- Below average
- Average
- Above average
- Very good
There are no specific rules for deciding what your soil quality is, but if you take into account the following guidelines you should be able to make a good guess of how your soil ranks.
- Shallow soils will generally be less than average.
- Sandy soils will generally be less than average.
- Shaded roots (e.g. due to a fence or hedge) in well-drained soil will help retain moisture and will boost the apparent soil quality due to slower drying in the summer.
- Hard (rocky) subsoils can prevent root growth and may have shallow topsoil.
- Soils with a pH that is far from near-neutral (pH 6.5 - 7.0 is ideal) may slow growth.
- Chalky soils are often shallow and raised in pH.
- Soils prone to waterlogging (unless tree planted on a mound).
- Low-rainfall regions may reduce vigour.
- You are unlikely to have very good soil unless you have basically average soil that has then been heavily worked with compost, and fertiliser over a period of several years (allotment soils are often in this category).
- Similarly, you are unlikely to have very poor soil unless nothing else grows either.
To help get a better idea of your soil characteristics it is a good idea to dig a hole, as deep as you can, to see how deep the soil is and what type of material lies underneath it - the subsoil. Try wetting some of the topsoil and then squeezing it gently in your fingers to get an idea of whether it's sandy (feels gritty) or clay (feels slimy) or whether it's the perfect middle-ground in-between, with an equal mix of sand, clay and organic material.
Another approach is to half-fill the a jam jar with water, then add a quarter jar of your topsoil. Replace the lid and mix well, then allow it to stand. After a short while the soil components will separate out so that you can see how much sand is in your soil.
Another simple method is the "bucket of water test". Dig a bucket-sized hole, pour a bucket of water into it and see how long it takes to drain. Too fast drainage (e.g. measured in minutes) could reduce vigour by losing the water and nutrients before the roots can grab it. An excessively fast-draining soil may absorb several inches of water per hour and the soil will become too dry in summer.
Too slow drainage (e.g. measured in days) could reduce vigour by waterlogging, partial suffocation of roots, rotting of roots, or by the soil remaining relatively cold. Excessive moss and algae will also be present in slower-draining soils, although moss/algae can simply be a feature of a shady location that remains damp, but not necessarily badly waterlogged. An excessively slow-draining soil may absorb less than an inch of water per hour and may remain waterlogged for long periods.
If you are not sure what your soil quality is, assume it is average.
Scion vigour
The scion vigour is the inherent vigour of the chosen variety that has been grafted on to the rootstock and is based on a 6-point scale:
- Small, e.g. Court Pendu Plat, Greensleeves
- Slightly small – e.g. Braddick’s Nonpareil, Grenadier
- Average – e.g. Charles Ross, Empire
- Slightly large – e.g. Katy
- Large – e.g. Howgate Wonder, Laxton’s Superb
- Very large – e.g. Blenheim Orange and Bramley’s Seedling.
In practice the scale is essentially a 5-point scale from small to large (with average being the mid-way point), but Blenheim Orange and Bramley’s Seedling are exceptionally vigorous and merit a separate category. The same principle applies to plums and pears, except the range of vigour in the varieties is less. There are more examples of variety vigour on our fruit tree height calculator here.
Many varieties on this website already have a vigour ranking set by us. If you disagree, or you have information on varieties that we have not assessed, please get in touch.
Note that whilst scion vigour has an important effect on the size of the tree, it has no affect on the size of the fruit.
Also remember that the natural vigour of the scion variety can be significantly affected by the age of first fruiting, since when a fruit tree begins fruiting it tends to switch some of its energies from growth to fruit production. Therefore if you encourage a young tree to start fruiting earlier in its life than it otherwise would, it will probably not reach the same size as one that has been left to develop at its own pace. (Encouraging early fruiting is therefore a useful method of controlling vigour if you have a bought a tree on a more vigorous rootstock than you intended).
Using the tree height calculator
We have applied the formula described here to many of the varieties listed on this website. If the data is available for the variety you are viewing, you will see a table with a matrix of tree heights by soil quality. We are working to add this feature to more varieties over time.
One of the advantages of this formula is that if you are planning a small orchard based around the popular apple MM106 rootstock, you will see that you might want to use MM111 for the weaker-growing varieties, and M26 for the more vigorous varieties, to achieve an overall balanced size of tree. Similarly you can use the St. Julien A rootstock to get a plum tree of the same size, and the Quince A rootstock to get a pear tree of a similar size.
The formula has been developed based on observations in the southern UK, which is a good (cool temperate) climate for many fruit varieties. It may not be accurate in other climates although the general principles will still hold. For example the apple M26 rootstock is known to be particularly variable in its performance in different climates and soil conditions.
Try out our fruit tree height calculator here.
If you would like to contact N. Buck, the author of this formula, please get in touch with Orange Pippin and we will forward your enquiry.
Disclaimer. Use this calculator at your own risk. We do not accept responsibility for errors or adverse occurrences related to the use of this calculator, and we may also update the calculations from time to time. We welcome your feedback on the accuracy of this calculator compared to your own observations.