People often hesitate to prune maples because of the sap. Cut a maple in late winter and it can drip for days. That looks like the tree is bleeding to death, but it is not. Choosing the right month is still worth a little thought, because it affects how well the cuts close and how much new growth you get.
The short answer: for most maples, the best times to prune are late winter, while the tree is dormant, or early summer, once the leaves are fully open and have darkened. Late-winter cuts may drip sap, which does not harm a healthy tree. Avoid pruning while the leaves are opening in spring and in late summer to fall. Remove no more than about a quarter of the live crown in one year.
Option 1: late winter
In much of the northern United States, late winter (roughly February to March) is the classic pruning window for deciduous trees. The tree is dormant, you can see the branch structure clearly without leaves, and the cuts begin to close as soon as growth starts in spring.
Maples are known for bleeding sap from late-winter cuts. Iowa State University Extension says the sap flow is unsightly but does not harm the tree, and there is no need to treat or seal the wounds. The tree is not losing a meaningful amount of its reserves.
Option 2: early summer
The University of Minnesota Extension suggests waiting until early summer to prune maples and other heavy bleeders, such as birch and walnut, if the sap bothers you. By the time the leaves have fully expanded and turned dark green, sap pressure is much lower and the cuts drip little.
Early summer pruning has another benefit: you can see which branches are dead, because they have no leaves.
When not to prune a maple
| Time of year | Why it is a poor choice |
|---|---|
| While buds are opening and leaves are expanding (spring) | The tree has just spent its reserves on new leaves, and the bark tears more easily |
| Late summer to fall | Cuts close slowly before winter, and pruning can trigger late growth |
| During a drought | The tree is already stressed; wait for normal moisture |
Dead, broken or hazardous branches are the exception. Remove those at any time of year, safely.
How much to remove
The International Society of Arboriculture’s guidance for mature trees is to remove only what is needed and generally no more than about 25 percent of the live crown in a single year. On large, established maples, the reasons to prune are usually narrow:
- Removing dead, diseased or broken branches.
- Removing branches that rub or cross.
- Raising the crown to clear a roof, walk or driveway.
- Reducing a branch that is growing toward a structure.
Avoid topping, which means cutting large branches back to stubs. It weakens the tree and leads to a dense mass of weakly attached shoots.
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Making good cuts
- Cut just outside the branch collar, the slightly swollen ring where the branch meets the trunk or a larger limb. Do not cut flush with the trunk, and do not leave a stub.
- For branches more than an inch or two thick, use three cuts: an undercut a foot or so out, a top cut just beyond it to drop the limb, then a final cut at the collar.
- Use sharp, clean tools. Ragged cuts close slowly.
- Do not paint or seal the cuts. The tree closes them on its own.
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Young maples: shape them early
The most valuable pruning a maple ever gets happens in its first ten years. Small cuts on a young tree prevent large cuts on an old one. Each late winter, look for two stems competing to be the main leader and remove or shorten the weaker one. Remove branches that grow at very narrow angles, which tend to split later, and space the main branches along the trunk. Raise the lowest branches gradually over several years rather than all at once. Silver maples in particular form weak, tight forks if left alone, so early structural pruning pays off.
Japanese maples
Japanese maples follow the same general rules. Light shaping and removal of crossing twigs can be done in late winter or in early summer after the spring growth hardens. Many are slow growing, so remove less than you think you need.
When to call a certified arborist
Work that needs a ladder, a chainsaw or cuts on branches over the house or power lines belongs with a professional. A certified arborist will also know local rules about trees near utility lines. The ISA Find an Arborist directory lists certified arborists by area.
If you are pruning because of dead branches or a thinning crown, check why a maple tree may be dying first. More seasonal care is in the Pruning & Seasonal Care hub.
Sources
- Plants to Prune in March, University of Minnesota Extension
- Sap is flowing from a pruning cut on my maple tree. Should I be concerned?, Iowa State University Extension
- Pruning Mature Trees, International Society of Arboriculture, TreesAreGood.org
Top photo: Dietmar Rabich, CC BY-SA 4.0, via Wikimedia Commons