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Pruning Maples, Birches and More
Now, as the leaves are disappearing (or accumulating on the lawn, demanding in a whiney voice to be raked up and used for mulch) I am pruning hardwoods like maples, birches and other deciduous trees and shrubs. For me, happiness on a sunny fall day is improving the looks and long-term health of trees by pruning – so I’m out doing some now most nice days.
It’s easier to see the form and structure of trees and shrubs at this time of year because the leaves are mostly gone. I know that some gardeners prefer to prune in the spring – I do fruit trees then – but not all trees can be pruned then. Maples and birches, among others, bleed lots of sap if pruned in March. So I do them now.
Before pruning a young tree, take some time to look at mature trees in your neighborhood. The best ones have open arms: their branches are well spaced and have branches angling off at a 45 degree angle from the trunk. Often these are trees that grow along a fence line or a dirt road so that they had sunshine coming from all sides as they grew.
Trunks too close together
You may also see some trees that have several fat trunks or stems growing almost parallel, reaching for the sky. These are the trees that split and break off in wind or ice storms. Why? An arborist might use the words “included bark.” This refers to bark that gets engulfed by the growth of 2 trunks that grow too close together. As the trunks grow fatter, bark between them is swallowed up by the two competing trunks, and creates a weak spot that can more easily split.
Recently I saw a large native cherry tree that had split in half. It was, according to my count of the rings, 65-75 years old and it was more than 50 feet tall. Sadly, it had twin trunks and one half split off and fell during a wind storm. I could see that fungus had weakened the wood – the seam between the two trunks was not a tight seal, allowing water and the fungus to enter. And now the remaining trunk is open to the elements and will not survive as long as it might otherwise.
If you have a young tree that has branches or trunks that are growing together and have a tight angle between them, you should act. You will need to remove one of the competing stems. This may seem drastic, and is best done before the stems are more than 2 or 3 inches in diameter. I removed a few recently while working at the Kilton Library in West Lebanon, NH.
Of course, removing a 2-inch stem also means you will lose all the side branches that are growing on it, too. Before unsheathing my big pruning saw I walked around each tree for several minutes. I looked at the two competing stems and tried to mentally erase one from the picture I was looking at. Would there be a big gap in the canopy? Would there be small branches that could fill in after surgery? Yes, there are always small branches that will fill in.
There are also “dormant buds” on trees that can produce branches if the tree “senses” a gap in the canopy. Trees, obviously, don’t have brains that tell them when to send out new branches. But there are stimuli such as sunshine coming through an empty spot in the canopy that will “tell” the tree to set out new growth.
At Kilton Library (where all the trees were planted in 2010) I studied the trees that I had pruned last year. I had removed some two-inch diameter stems that were growing together too tightly. I was pleased to see that the trees looked full. No big gaps. In general, removing a big stems or branch does not seem so drastic after it’s gone – even though it seems scary when it’s time to cut. And removing a big branch helps the tree to be more open, thus allowing every leaf to get some direct sunshine, which is good.
Cherry tree split due to included bark
At the back of the property there is a maple that “wanted” to send branches over the fence and reach out for sunshine on the neighbor’s property. I noticed that one branch I had removed last year – only an inch in diameter or so – had sent a new branch back over the fence. Amazingly, it had grown 5 feet in one year! Interestingly, the leaves on it were nearly twice the size of the leaves on the rest of the tree. So trees will keep on producing branches to take advantage of sunshine, no matter what we do.
So if you haven’t taken a good look at the arrangement of trunks and larger branches on your trees, this is a good time to do so. You might be able to prune them yourself, but you might have to call an arborist who can take out a large branch or trunk if need be. It would be money well spent – 50 years from now you just might lose a tree, or half a tree, if you don’t do so.
Henry Homeyer is the author of 4 gardening book, and a children’s chapter book, a fantasy-adventure about a boy and a cougar. His web sites are www.gardening-guy.com and www.henryhomeyer.com.