Consider this before pruning your trees this winter

A common piece of advice you will hear is to prune trees during the winter while they are dormant. I often give that advise myself and, for most kinds of trees, that is a good rule to follow.

However, just because winter pruning is preferred for most species of trees, that doesn't mean it is appropriate for all trees in Michigan.

The problem lies with the fact that more than 50% of trees in Michigan cities and towns are maple trees, putting them squarely in the majority of trees.

Maple trees pruned during the winter are prone to “bleeding” sap from pruning cuts done during the late winter through early spring. This directly corresponds with the time maple sap run occurs.

When maple syrup makers drill holes in the trunk of maple trees for placing their taps, they are intentionally creating a wound that severs the vessels inside the tree from which sap flow. It is a carefully planned trauma that allows for the controlled collection of sap.

When a maple tree is pruned before the sap run, the pruning cut also creates a trauma that will allow sap to flow.

Many gallons of sap can flow from even a relatively small pruning cut. All of that sap can become unsightly as it flows out and stains the branches and trunk near the cut. Insects, mostly harmless, are also attracted to the sap due to the sugar content. Sap that collects can ferment on warmer days and attract even more insects.

While it can be alarming to see, the volume of sap lost from pruning will not harm the tree. Maple trees tapped for syrup can provide up to 80 gallons of sap during an ideal season. However during a typical year, the yield is much smaller, around 10 to 20 gallons would be closer to what could be expected.

If all of that running sap and resulting stain is disconcerting to you, wait until the sap run is over to prune your maple tree. The maple sap run ends when the temperatures stay above freezing and the tree buds begin to open.

I often wait until June to prune maples. That way, the sap run is completely over and the tree has plenty of time to begin healing while the tree is making good growth.

On the other hand, if you are pressed for time or you don’t mind looking at sap flowing from your pruning cuts, you can still do your pruning knowing that you will not be harming your maple tree. Plus you’ll get a head start on your spring gardening tasks.

Speaking of which, the first day of spring is only six weeks away.