By Anne Alt
Many homeowners see landscapers working around trees and may assume what they are doing is correct. Landscapers usually are not well educated in tree care. There are many local examples of two landscaping practices that are bad for tree health: volcano mulching and raised beds around tree trunks.
Landscapers often pile mulch around tree trunks in deep mounds. Professional foresters call this volcano mulching. It can cause rot and disease, shortening the life of a tree.
Mulch should be spread around tree trunks in a donut shape. Pull mulch away from the tree trunk, leaving a few inches of space between the mulch and the trunk to expose the soil surface. Do not pile mulch more than three to four inches deep. Mulch that’s too deep deprives the roots of oxygen and causes a problem called root girdling, described below.
Bark or wood chip mulch improves soil health. If you can, create a mulch ring as wide as the tree canopy, that’s ideal for the tree. If not, make it as wide as you can.
Grass competes with the tree’s roots for moisture and nutrients. Removing some grass around the trunk also creates a border to minimize the risk of lawn mower blades hitting the trunk and damaging the tree’s circulatory system, another way that trees are often killed.
Lately I’m seeing more raised beds around tree trunks. I suspect that the people doing it have no idea how raised beds harm trees. Tree roots need oxygen. If you bury roots too deep, they rise towards the surface. In a confined space, they circle around creating a condition called root girdling that shortens the life of the tree.
The photo above shows how tree roots look when a raised bed is removed after years around a tree trunk. Trees with girdled roots are gradually dying. Do not do this to your trees. Instead, use mulch over soil at grade level. Plant flowers in the mulched area, leaving some space between plants and tree trunk. Your tree will be much happier than with grade level plantings instead of a raised bed.
Climate change makes it more important than ever to look after the health of our trees. Let’s work together to help our trees thrive.