How to Garden Under Established Trees
We often receive questions about how to garden under established trees. Usually that’s because gardeners don’t want to risk damaging the tree. So they reach out for help understanding what to plant under established trees in their gardens. For instance, Barbara from Lancaster, CA wrote in to ask for help about gardening under her very old tree:
“We just purchased a house with a beautiful, very old birch (weeping) tree in the front yard. A large area around the tree is raised due to roots and many years of growing. We’d like to keep the tree as it is huge. It was probably planted when the house was built. That was 1965. We need to roto-till the entire yard to put down a new lawn. What should we do about the raised tree area? We could put a large, very large circular brick wall around it but then could we put dirt over the roots near the surface to plant some small shrubs, flowers? What to do, what to do?”
What an Arborist Shares About Gardening Under Established Trees:
Guest contributor Katy Bigelow chimed in to share her perspective Barbara’s challenge around planting a garden under her big, old tree. She began by congratulating Barara for purchasing a piece of history and working to preserve it. But then she really dug into the challenge of gardening under big, old trees like this birch.
Steps to Avoid when Gardening Under Big, Old Trees.
First, arborist Katy advises that you do not till up the soil under big trees. But, if you do need to till for some other reason, be sure to keep the tiller well away from the trunk of the big tree.
In fact, Katy advises that the tiller should stay out of the entire drip line of the tree.
And just to chime in a bit more on tilling, usually we avoid tilling as much as possible in all gardening circumstances.
Why Avoid disrupting the Drip Line of Established Trees.
If you aren’t aware, the drip line of an established tree (or any tree) is area directly located under the outer circumference of the tree branches. More importantly this is where the tiny rootlets are located. And these are the tree roots that take up water and nutrients for the tree. So, a tree can be significantly and sometimes unpredictably damaged once these roots have been disturbed. Furthermore, knowing how specific roots connect to the upper parts of a tree is little understood. Therefore, you might end up damaging an area connected to a branch that you’d really like to save should you break it with tilling.
Don’t Build a Retaining Wall Under Big, Old Trees…
Second, arborist Katy suggests avoiding building retaining walls under established trees. That’s because adding a bunch of new soil over the roots is also isn’t great for a tree. And in most situations like this, the retaining wall is built in order to add more soil.
How Much Soil Can You Put Over the Roots of an Established Tree?
Third, Katy does share that it is okay to add about 2″ to 4″ of compost or mulch over old tree roots. That’s because this thin layer will help keep roots cooler and warmer when they need it most. And it can reduce the effect of soil compaction. However, too much more soil than that can actually cause the roots to smother. And this soil should not be tilled in!
Exposed Tree Roots Might Be Telling You Something…
Fourth, Katy reminds us that exposed surface roots on your established tree might also be pointing to your type of soil. When trees show roots on the surface, you may have clay soil. Or the tree might just be trying to get light and air from an easier place than in heavy compacted or dense earth.
Arborist Katy’s Final Thoughts on Planting Under Big Trees…
Katy concludes sharing: People do install plants under trees and getting the right plant for the right place will help them succeed. But often one or the other wins, no matter how much love is given. So, if you do plant under your established tree, it is most important to take care not to water the tree trunk as you’re watering the new plants. That’s because a constantly wet trunk can becomes a thriving fungus community fast. And when that happens, your tree may fail quickly.
How to Plant Under Your Established Trees?
How to plant under established trees is a question that also comes up often. But we’d point out that it isn’t just a question of “how?”. In fact, we should be asking what can we plant under big old trees so both the tree and the new plants thrive.
Do – choose very small plants. That’s because they only require very small holes. And that means you won’t be as likely to disrupt roots when you dig them in.
Do Not – Tear up the tree roots and leave them ragged. Instead, cut any tree roots cleanly when you plant.
Do – Water each new plant deeply right after planting.
Do Not – As Katy said, saturate the tree trunk as you water.
If you need more help gardening under established trees, be sure to sign up for more information about our online gardening programs. That way you’ll be first in line when we open enrollment!