Roots keep trees anchored as well as take up water

Q: I have what I believe is a fan-tex ash tree in our backyard. There are some roots that are on the top of the ground that are lifting up a concrete edging. Is it safe to cut these roots out so I can put the concrete edging back down? Attached are pictures. The first two are the roots in question. The third is an overall picture of the tree. I would estimate the roots have a diameter of 4 or 5 inches (but that's just a guess).

A: Each situation is a bit different, so thank you for including pictures. The tree is planted in a tree and shrub border with rock mulch. This border planting is on the perimeter of what used to be a lawn. The tree has four shrubs at its base. The lawn area now appears to be bare ground.

These roots grew into the lawn when the lawn was there. Now that it is gone, the tree is getting water from some other sources. My guess is that the tree is now getting its water from the four shrubs at its base and, if you look over the wall, perhaps from your neighbor.

I think you are in good shape to remove these surface roots over time . But tree roots also function as anchors for the tree and help to keep it from blowing over . So even though the roots lifting your curbing may not be taking up much water for the tree, they still work to keep the tree anchored .

There is a danger that if all the offending roots were removed it might begin to lean toward your neighbor, especially if there are strong winds . I think you could remove a couple of offending roots without too many problems. But at the same time you would want to encourage more roots in the area around the trunk.

You would do this by staking the tree to keep the roots from moving, increasing the water and fertilizer near its base and thinning the canopy so that wind passes through it more freely. When you cut and remove the roots, clear away all soil from the place where the cuts are to be made. Disinfect your cutting tool with alcohol or heat. Bleach can be used but it will rust tools if you do not oil them afterwards. Leave the cut roots exposed to the open air for a few days before putting the soil back.

Q: I am thinking of removing all of the small rocks in my front yard where we grow roses and putting wood mulch down. My concern is wind blowing the mulch into my front doorway and having a nuisance with our entry. We have eight 11-year-old Carolina cherry trees on the northwest side of our home. I am considering replacing all the small rock around the trees with wood mulch. Will this help?

A: Roses and Carolina cherry laurel all do much better in organic, or wood, mulch than rock mulch. You will have nothing but problems if you continue to use rock mulch with these plants.

If you use coarse mulch like we have at the University of Nevada Cooperative Extension Master Gardener Orchard in North Las Vegas, it will not blow away as the rough edges and the various sizes seem to interlock even in winds up to 70 miles an hour. Make sure you put down at least 4 inches of mulch.

Carolina cherry laurel does not do particularly well in our climate, particularly in rock mulch. They like protection from winds and late afternoon sunlight, so eastern and northern exposures away from strong winds are usually best. They like heavily amended soils and they love to have organic mulch. That northwest exposure could be a killer for you cherry laurels .

Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by e-mail at morrisr@unce.unr.edu.