Can a Full-Size Japanese Maple Be Pruned Back Smaller?

Timing

• Although a Japanese maple tree handles pruning quite well, it's best to restrict pruning to times of low growth, which include winter, early spring, midsummer or late-fall. The tree grows most actively during late spring, early and late summer, and early fall, so avoid these periods. Pruning during periods of high growth can cause loss of sap and increase the chance of insects or disease getting into pruning wounds, putting extra stress on the tree. Pruning during late fall or winter after leaves have fallen also helps you see the branches clearly when deciding where to make cuts.

Pruning

• You can prune away major branches on a full-size Japanese maple to reduce its size, but you shouldn't remove more than half the total mass of the tree, according to experts at Davidsan's Japanese Maples. Fine Gardening warns that removing more than one-fifth of the tree's crown might stimulate growth of spindly new branches, so prune gradually and with care. Exactly how you prune also depends on your goal. To shorten the tree, concentrate on upper branches, removing some completely and cutting back others to a point where new growth will look attractive and fill in well. If you want to decrease the tree's width, prune side branches back in a balanced way so that the tree becomes less wide on all sides, but never remove more than one-quarter of the foliage on any branch, because this can starve the remaining branch of nutrients.

Details

• When choosing branches to remove, avoid cutting off any that are larger than half the diameter of the tree's trunk, because this can stress the tree. For an older tree, it's preferable to limit yourself to branches that aren't more than one-quarter or one-third of its trunk diameter. Remove branches that cross and rub on other branches, because these can injure the tree's bark, allowing easy entry for pests. Make cuts close to the origin of the branch, leaving the branch collar on the tree. This is the slightly raised area beneath the branch, where it attaches to the tree. Always use sharp pruning shears or a pruning saw and sterilize your tools between cuts by soaking them in a 50 percent solution of rubbing alcohol or a 25 percent solution of household bleach.

Other Factors

• A Japanese maple tree responds best to pruning when it's healthy and unstressed, helping it put out strong new growth. Keep the tree well-watered in any year you're planning to prune, especially during summer dry spells or in fall as winter approaches. Adding a thick layer of organic mulch in the spring helps conserve soil moisture during hot summers, while also keeping down weeds that compete for soil nutrients. Fertilizing the tree in early spring also helps it respond well to pruning. Use a complete fertilizer such as a 16-4-8 formula labeled for use on trees. Apply it at a rate of 2 pounds of nitrogen per 1,000 square feet under the tree, or about 12.5 pounds of a 16-4-8 fertilizer.