My greatest garden nemesis — aside from slugs and too much shade — is the source of one of those other problems, namely, Norway maple trees. First to leaf out in the spring, and last to drop its leaves in the fall, this genuine thug of a tree evolved to dominate. And dominate they do.

Not only do the extra large leaves of this tree work to shade out anything that might attempt to grow underneath it, its expansive root system extends out, and up to the surface, with a solid network of roots that pretty much eliminates that possibility. Add to that a copious amount of seeds produced and dropped, which results in thousands of seedlings, and you’ve got a tree bound to succeed.

Norway maple bonsai tree. Photo by Lynette Walther.

No wonder these invasive trees are taking over woodlands. And there’s more not to like about Norway maples than just those big leaves. Turns out, in the areas where they have invaded natural woodlands those leaves are destroying the leaf-litter base, which, in turn, has negative consequences for native wildlife because it breaks down too quickly. Norway maple leaves contain higher nitrogen levels than the leaves of other native deciduous trees. While that makes them a great addition to the compost pile, that also means they decompose more rapidly than the native trees’ foliage. But, in the meantime, those big leaves tend to form nearly impenetrable mats that if left in place will kill lawns underneath, or make it impossible for spring-flowering bulbs to find a way through them.

While other trees have long-since dropped their leaves, Norway maples are just now getting around to that process.

If you are “blessed” with these trees, I encourage you to see about having them removed. One of the reasons they became popular was they grow so quickly, providing a huge shade tree in just a few years. However because of that rapid growth pattern, they tend to be especially brittle. And because they leaf out early, and hold their leaves late, they are vulnerable to wind storms with their canopies serving as levers. Several of the especially large specimens have crashed down in my neighborhood; more than one of them crashed through the roof of the nearest house. They do make passable firewood, after all. But if removing them is not an option, mind those mats of leaves on the lawn and where you have bulbs planted.

Norway maple gets cut. Photos by Lynette Walther.

But forget bagging and removing them entirely, same for the leaves of other deciduous trees and shrubs. Turns out every fall there are tons of fall leaves that unnecessarily end up in landfills. And we are learning of the actual benefits of some of those leaves when they are allowed to remain in the landscape. Eventually fallen leaves drift around the bases of perennials and shrubs, and there they provide winter cover for those plants, and over time decompose to add slow-release nutrients right where they are needed.

Even more importantly, fall leaves provide nesting places and winter cover for a variety of beneficial insects. The dramatic decline in insect populations in recent years has set off alarm bells, as we have also witnessed a decline in bird populations as well. No matter what the bird — even those seed eaters and nectar birds like hummingbirds — all birds feed insects to their young. Considering that more than 95 percent of insects are either benign or beneficial, we get the idea that helping out the insect world is to our advantage.

What this means is that a light layer of leaves left in ornamental or even vegetable beds is perfectly acceptable, preferable even. We just want to avoid thick mats. Mowing the lawn late in the season can quickly shred leaves there, making them decompose faster to provide added nutrients for the grass. Or, rake lawns, and add the leaves to the compost. Either way you will be putting those leaves to work, while keeping them out of the landfill, and giving Nature a helping hand in the process.

filed under: