Is May a good time to prune an amur maple? It seems to form a canopy of leaves in the summer, so I’m concerned if I prune about 25% off the top now it may not leaf out sufficiently.
Thank you for contacting the Toronto Master Gardeners.
In general, the best time to prune an Amur maple (Acer ginnala) or any maple tree is during the winter months and possibly in the very early spring, when the tree is dormant. Pruning the tree in May is not advisable unless one is removing dead branches. You mention pruning “25% off the top”–it is unclear how big the tree is, or if it is multi-stemmed, or why you want to prune it “off the top”. Amur maples can be grown as a single-stemmed specimen tree or as hedging; is hedging your intention?
Amur maples are generally smallish trees with a rounded habit; the leaves become brilliant red in the fall. Even though Amur maples can tolerate heavy pruning, most references recommend pruning during the winter months (when the tree is dormant) or during the summer–maples tend to ‘bleed’ sap during the spring when pruned or cut–considering the amount of branches you want to prune, May would definitely not be the best time to prune. You should wait at least until the summer months. Furthermore, once the leaves have fallen in the late fall, it would be easier to see where the tree should be pruned.
Perhaps you can cut back a few of the branches once the tree has completely leafed out; but cutting “off the top” now would not be recommended.
Here is an Article from our library with links giving advice and techniques for pruning the smaller Maples.