Japanese maples caught short

Rx for when leaves don't fall

You may be noticing something odd about your own or others’ Japanese maples, even at 45 mph. Why are they still holding leaves into winter? What can you do?

 "Is it a bad thing?"

Judging by recent email queries, quite a few Japanese maples failed to drop their leaves this year.

“They just sort of faded to light brown but didn’t fall. They are all still there,” says J.P. “Is this a bad thing? It’s a pretty tree, maybe 15 feet tall. It came with the house so we don’t know what to expect now, whether this is normal.”

When December arrives and all the other trees are bare but your Japanese maple is still holdng its foliage, the tree will probably need help.

When December arrives and all the other trees are bare but your Japanese maple is still holdng its foliage, the tree will probably need help.

Not normal, but common

It’s not normal but it is common. The shedding of leaves is a living process. Once the tree feels colder, longer nights each leaf accelerates its transmission of nutrient-rich starch, pouring out into the tree’s shoots (buds) and wood all that it’s making plus its own substance. As it does so it gradually plugs the openings that brought it water and carry the starch, until finally the leaf base separates cleanly from the tree.

Sometimes Japanese maples in the open, evolved for the understory where big trees’ canopies stave off the first rounds of winter cold, don’t get enough time between their first cold cues and a freeze hard enough to kill leaves. Leaves killed by cold cannot continue the living process of leaf shed.

Holey maple, stressed tree

When that process is interrupted, the leaves are eventually pulled off by wind and the weight of snow and ice. Their points of attachment, incompletely plugged, are holes rather than sealed openings. Moisture from within the wood can escape through those gaps. That will create stress down the road.

The water stress may present as tip dieback - small twigs may die. It may result in foliage being smaller next year than it could be, and overall growth less. The tree may still be losing more water than it can take up when it’s very hot and dry the next summer, and lose foliage or more branches.

We can’t change the fact that the leaves didn’t finish separating themselves from the tree but we can intervene to help the tree weather the aftermath. We can also guard it against additional stresses.

What you can do

Give it regular water next year, checking by probing the soil that what you apply is enough to keep the top few inches of soil beneath the tree moist – not soggy. Keep that up all season, especially through the heat of summer when the tree is using the most water.

Mulch the root zone well and protect its roots. That is, if work you plan to do or have done to the house and yard requires digging within the tree’s branch-spread, hold off a year.

If there is an ice storm while the leaves remain on the tree, think about putting props under main branches. That’s because not only will the tree’s wood become ice-coated, the foliage will collect ice, too. So much extra weight on each branch could cause breaks.

If the tree is exposed to afternoon sun in winter, shade the trunk. More on the why and how of protecting the trunk, in Pretty Protected Maple Trunk and What’s Coming Up 68.