If you have large-growing Trees in your yard, sooner or later you may be dealing with trees with surface roots.
Surface roots can make it a challenge to maintain a nice level lawn under your shade Trees. Large Tree roots become a tripping hazard and also make it hard to mow under the Tree. They can even cause sidewalks nearby to heave and crack.
What causes surface rooting and what can be done about it?
Getting the answers right here is very important, because a misstep could jeopardize the health of a cherished old Tree. We’ll answer these questions and also tell you what you can do to avoid problems in the future if you’re planting a new Tree now.
What Causes Surface Rooting?
Some kinds of Trees are predisposed to having shallow roots. Trees like Norway Maple, Red Maple, and Silver Maple are some well-known examples, along with Willow, Aspen, Pin Oak, and Beech.
But any large-growing Tree is likely to develop surface roots when it reaches a certain age. That’s just how Trees grow.
Most Tree roots grow wide and shallow.
Contrary to popular belief, Tree roots usually do not grow very deeply unless the soil they’re in is quite sandy and loose. You might be surprised to know that very few Trees have a taproot and that the majority of Trees’ roots are found in the top 12 inches of soil.
When main roots lying a few inches underground get big enough, they break the surface. Rain and wind may then erode the soil, leaving the roots even more exposed.
Roots are shallower in poor soils.
Surface rooting is most common in compacted soils like that found in many urban and suburban lots and even in the country where soils have lots of heavy clay in them.
Roots need to breathe.
Roots need oxygen, and in tight soils they grow more shallowly to reach the oxygen they need to survive. Surface roots are the result of Trees adapting to their environment and making the best of a less-than-ideal situation.
What Can I Do about Surface Roots in My Lawn?
If you have a big Tree in your lawn and surface roots are a problem, there are a couple of things you can do.
Don’t cut big roots.
The thing you should NOT do is to cut the offending roots. Cutting large roots can give diseases and insect pests an easy entry point. It can also make the Tree less stable and more likely to blow over in a storm. Not to mention that cutting one big root can kill thousands of tiny “feeder roots” attached to it that allow the Tree to take up water and nutrients. Cut too many roots and you’ll have dieback in the canopy or possibly the death of your Tree.
Consult a qualified arborist if you think cutting roots is the only viable option.
Topdress with a light soil mix and seed.
A better plan for dealing with surface roots in lawn is to put down 2 inches of a 50-50 mix of topsoil and compost around the Tree and sow the area in late summer with shade-tolerant grass seed, keeping it well watered. If the roots are still too prominent a year later, you can add another 2 inches of the soil mix and reseed, but never add more than 4 inches of soil to the area beneath an existing Tree.
Remember that roots have to breathe, and it is possible to suffocate a Tree by changing the grade too much.
Instead of grass, you could plant a drought-tolerant groundcover under the Tree which would save you the trouble of having to mow in that area—or, mimic nature and consider using moss as a groundcover!
Mulch is the best solution.
The best plan, however, is to put down 4 inches of organic mulch—preferably wood chips—around the Tree.
Wood chips will help to level out the area while keeping roots cool and moist and allowing oxygen into the root zone. Don’t put down more than 4 inches, though, and be careful not to pile mulch against the trunk. Pull it away so that it doesn’t hold moisture against the trunk and encourage disease or give critters a place to hide while they nibble the bark.
How Can I Prevent My New Tree from Having Surface Rooting Problems in the Future?
When choosing a Tree, avoid notorious surface-rooters.
If you have clay or compacted soil, your Tree will probably have some surface roots eventually, but some Trees are worse offenders than others. If surface roots will pose a problem in your planting area, steer clear of the following:
Maple, Freeman (like Autumn Blaze®)
Maple, Norway (like Crimson King)
Choose a Tree with a relatively deep root system.
Given enough time and an average to heavy soil, just about any large Tree will have surface roots. However, these choices usually pose less of a problem:
Will a smaller Tree work for you?
Trees that mature at under 30 feet tall will usually not have roots large enough to cause major problems. Maybe one of these smaller Trees could do the job:
Golden Chain Tree
Purple Leaf Plum
Seven Son Flower
Plant your Tree at the right depth.
Don’t plant your new Tree too deep to prevent having to deal with trees with surface roots. Having the mindset from the start will allow your tree to just grow deeper roots from the start! Young Trees need to breathe just like older ones do, so plant your Tree at the same level it is growing in the pot or even a bit higher—Bower & Branch™ recommends planting 2 inches above grade.
Don’t plant the rootball higher than 2 inches above the ground, though. If your Tree sits too high, its roots may dry out, and it may also be more vulnerable to freeze damage in the winter.
Give it room to grow.
Give your Tree space if there is pavement nearby. Large-growing Trees should be planted 6 feet away from paved surfaces if possible.
You may want to use your Tree as a street Tree and plant it in the Tree lawn between the sidewalk and the street. In this case, only plant a large Tree if you have a generous Tree lawn that’s 8 feet wide or more and have no utility lines overhead. If the planting area is less than 8 feet wide, choose a medium or small Tree that won’t outgrow its space.
Some cities have restrictions on which Trees can be planted in right-of-ways. If you’re a city dweller, check with your local urban forestry department for specific guidelines on planting street Trees and a list of suggested Trees for your area.
Choose mulch instead of turf.
Make a decision early on to surround your Tree with mulch instead of trying to grow grass right up to the trunk so you don’t end up dealing with trees with surface roots. Grass invites foot traffic, which leads to compaction, which depletes soil oxygen, sending roots to the surface, gasping for air. (Well, maybe it’s not that dramatic, but you get the picture.)
In short, keep your Tree breathing easy and you’ll breathe easier, too… under the shade of a magnificent, healthy old companion!