I live in Thornhill, near Steeles Avenue West. The tree is about 4 years old (in my garden). The soil is not too bad and it gets some sun and some shade. It seems pretty healthy and has a diameter of about 3′ and a height of about 3′. Can it be pruned and how should I do it? I am a member of the Society even though I don’t live in Toronto.
Japanese maples are beautiful specimen trees and wonderful focal points for any garden. In general, the spread of Japanese maples can be altered somewhat, but not the height. If you remove the top you will lose the form of the tree. Young trees are prone to thin, whip-like branch growth that many owners feel detract from the overall appearance of the tree. However, these wispy branches can grow into strong scaffold branches, and their early pruning encourages more growth of these spindly branches.
Japanese maples are not very fussy in terms of when they can be pruned, however spring is not the best as the sap is running now. Pruning in winter will allow you to clearly see the structure of the branches you are trying to shape and pruning in summer gives you a good perspective on how the foliage fills out the overall shape of the tree, and as well as on the health of individual branches. Prune out any dead branches and twigs and any crossed branches. Pruning in summer is also less likely to encourage new branch growth, but avoid pruning more than 20% of the crown, and no more than a quarter of the foliage on any parent branch. Removing too much foliage at one time inhibits the tree’s ability produce nutrients and can expose the inner branches and trunk to sun damage. It is best to prune over a few years only taking off some branches each year. When cutting off a branch, follow it down to where it attaches to a main branch and cut it there. Cutting back to main branches thins out the crown and allows more air flow and a greater resistance to disease. If you cut only the end of the branches, the buds remaining on that branch will grow in random directions and wreck the natural elegant form of the tree. Don’t prune these trees in the heat of summer – temperature greater than 26 Deg C
This article contains detailed information on good pruning practices for different types of Japanese maples, and how to sustain and enhance structure as the tree grows. You may be also interested in the Toronto Master Garden’s guide to growing Japanese maples found here.