What can I do about exposed tree roots?
"Fielding Questions" columnist Don Kinzler answers questions about roots running on the surface, as well as birch trees that are not leafing out and how to handle the nuisance of tree seedlings in flowers.
Q: We have two maple trees in the backyard with roots running on the surface. What can we do with this issue? — Jim E.
A: A tree’s root system is much shallower than we often consider. Tree roots spread more horizontally than deep, with most roots contained in the upper 1 to 2 feet of soil, radiating out from the tree.
As trees age and roots thicken, it’s natural for parts of larger roots to extend above the surface. Some tree species are more inclined to develop surface roots, such as maples. When we walk through a forest, we often need to watch our step, so we don’t stumble over roots protruding from the surface. It’s a natural part of the tree’s system.
Some sources have recommended cutting and removing the offending roots, indicating it might be safe to cut and remove one large root per year. This is NOT recommended by many universities, including Cornell and New Mexico State University. Cutting these large roots can diminish a tree’s natural support, making it more prone to uprooting in severe storms. Cutting roots can allow disease and rotting organisms to enter and can lead to branch death in the tree’s canopy.
To deal with surface roots, you might opt to do nothing, leaving them exposed, as nature does. You can mitigate the effects by filling around the roots with no more than 1 to 2 inches of good quality, non-heavy topsoil. A too-deep layer will smother root systems and lead to tree decline. Adding compost is good, instead of adding heavy clay soil.
Another option is to mulch the area around the tree and between surface roots with shredded wood products, keeping the mulch away from direct contact with the main tree trunk.
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Q: I have two birch trees that are not leafing out. Both are 5 to 6 years old so a good size. They were healthy and vigorous growers last summer. Any idea what happened? Was it our strange fall weather? Some branches snap when tested; some do not. Should we make campfire wood out of them or wait and see if they come back? — Deb G.
A: Birches love moisture, and no matter how we water, nothing seems to satisfy like a good soaking rain, and last fall was dry in many regions. Birches went into winter stressed in many locales.
Moisture-stressed birches are more susceptible to winter injury, especially on upper branches. Upper branches on many of these trees are slow to leaf out this spring. You’re not alone, as I've been getting many questions about birches this spring. I'm recommending that we all wait for at least two weeks before taking action. By early June we should know if branches are dead, or if they are just slow.
In the meantime, birch trees would love a good, slow soaking underneath the tree's canopy, by letting the hose slowly trickle. Watering will help reduce stress until adequate rainfall returns.
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Q: Every year we get tree saplings growing in or flower beds. We would like something that kills the saplings but not flowers and other plants. Please advise us. — Glenn C.
A: I can appreciate the annoyance of tree seedlings in flowers. My wife, Mary, and I have Siberian elms that drop seeds all over our flower beds and the seeds sprout almost immediately. Tree seedlings can be a nuisance, and they grow very quickly in the centers of perennial flowers, making removal difficult.
There are no chemicals or herbicides that will selectively kill tree seedlings without damaging flowers and other plants, once the tree seedlings are growing. There are several options to rid flower beds of these seedlings. Although it’s labor-intensive, I hand-pull small tree seedlings, which is easier when the soil is wet or the seedlings are small. Larger seedlings can be cut off deeply below ground level and usually won’t regrow, if removed low enough.
Although there are no herbicides that can be safely applied over the tops of existing flowers to selectively remove tree seedlings, there are ways to diminish the problem before tree seeds sprout. To prevent tree seeds from successfully germinating, pre-emergent herbicides, such as Preen, can help somewhat. It prevents or kills seeds as they sprout. It has no effect on tree seedlings that are already growing, but it can help reduce future seed from popping up in flower beds. It's safe to use on established flowers, since it only kills germinating seeds. Follow label directions for effective application.
If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at firstname.lastname@example.org. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.