Last week, I described the many stresses urban and suburban trees suffer because of where they live. We don’t have to sit back and watch our trees suffer those stresses, because there are a number of things we can do to make our trees happier and help them live longer.
Trees may be planted in lousy soil, but it doesn’t have to stay lousy. If a tree is mulched out to the drip line or at least out as far as you aesthetically can stand, that mulch will feed the critters in the soil making up the soil food web. Over the years, they will make major improvement to the soil in which the tree is growing.
Benefit to the soil also happens if you plant ground cover under the tree out to the drip line. If ground cover is planted to replace turfgrass you will have taken away a major source of stress — the competition between the grass and the tree. There are lots of groundcover plants from which to choose. English ivy, vinca, ajuga and pachysandra are all popular. They stay green all year and need no water or fertilizer. When the groundcover fills in, it serves as a trap for falling leaves, which in turn feed the soil food web. Trees and air pollution offer us a serious conundrum. Trees are major players in pulling pollutants out of the air and water. They work at cleaning up our mess.
The problem is we have greatly reduced the number of trees we have and the emerald ash borer has killed millions of ash trees. The trees that are left cannot handle cleaning up the volume of pollutants and amount of acid rain, and they in turn suffer from those two serious environmental problems like all the rest of our plants.
Certified arborists have for decades recommended that homeowners with large shade trees have them pruned on the inside every four to six years. Thinning out some of the branches in the central part of the tree’s canopy allows air to move more quickly through the foliage. This step may not deal with air pollution and acid rain, but the tree, because it is healthier from the pruning, can better defend itself from those stresses.
Another benefit of using mulch or ground covers under your trees is that the lawn mower and the dastardly string trimmer can’t get close enough to the trunk to do any damage.
The biggest problem caused by trees growing between the curb and the sidewalk is the roots growing under the sidewalk, causing it to rise and crack. The only solution I feel is logical is to get rid of the tree and fix the sidewalk. Almost every community in southeast Michigan has very specific rules about replacing a street tree. They will usually have a list of species considered appropriate to be planted between the curb and sidewalk.