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Barbara from Lancaster, CA writes:

“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?”

Hi Barbara, Katy here,

How great is is that you have purchased a piece of history and are interested in preserving it!?!

I’m not sure why you are rototilling to make a new lawn- perhaps drainage problems you’re trying to remedy? In any event, keep that rototiller out of the “drip line” of the tree. The drip line is area directly located under the outer circumference of the tree branches. This is where the tiny rootlets are located that take up water and nutrients for the tree. A tree can be significantly and sometimes unpredictably damaged once these roots have been disturbed. Furthermore, knowing how a specific roots connect to the upper parts of a tree is little understood – you might end up damaging an area connected to a branch that you’d really like to save.

Building a retaining wall to with the intention to add a bunch of new soil is also isn’t great for a tree. However, covering the surface roots with 2″ to 4″ of compost or mulch will help keep roots cooler and reduce the effect of soil compaction. Too much more soil than that can actually cause the roots to smother. Your surface roots might also be pointing to your type of soil – clayey? Not well drained? The tree might just be trying to get it’s light and air from a easier place than in heavy compacted or dense dirt.

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. If you do plant it is most important to take care not to water the tree trunk as you’re watering the new plants. A constantly wet trunk can becomes a thriving fungus community fast.

Good luck!

_______

Barbara, thanks for writing in. Robin here. I just had to chime in on this as well. So often clients believe rototilling is the answer to renovating a lawn space, when often it isn’t necessary. You may just need to have it thatched, aerated, limed, composted, seeded and then properly mowed and watered. Tearing all of it out and starting over doesn’t always solve on-going lawn issues. But, as Katy hinted at, we aren’t quite sure why you’re planning to till, so it’s difficult for us to know for certain. If you do till in that area and you hit some bigger roots that have expanded out of the “zone” Katy indicated, be sure to stop the tiller and use a sterile saw to cut the root clean on the side that connects it to the tree. This will help the tree help itself in the long run. If you leave the roots torn up, it may be harder for the tree to recover.

Katy also hinted at knowing your soil. I highly recommend you order a soil test to know what kind of soil you’re working with, what pH you have and what its nutrient situation is. This will help you choose the right course of action for preparing your soil to keep both your lawn and your trees (and anything else) happy. University of Massachusetts at Amherst has a soil testing lab that is relatively inexpensive and very comprehensive. You’ll find details here.

Thanks for writing in and have fun in the garden.