According to the ISA Arborists’ Certification Study Guide, girdling roots are ‘roots that grow around or across the stem of other roots. As the trunk and roots increase in diameter, these roots may begin to choke or girdle the tree. …The compressed stem weakens the tree and leaves it more prone to failure.’
Far too often I visit client’s gardens where there is at least one tree not growing well. This is usually due to planting the tree too deeply from the beginning. The tree can get collar rot from the soil being too close to the trunk of the tree, or girdling can occur later on. Both will kill the tree. It is not the depth of the hole that is important when planting – it is the width that gives roots room to spread and stabilise the newly planted specimen.
Because of our sandy topsoil in our new garden, I have found that following a heavy rain, the topsoil has moved and often banks up against the trunk of some of our established trees. About 4 months ago, I noticed that an existing fruiting pear was not doing at all well. It had lichen starting to grow on it, which I have found is not a good sign for tree health.
When I had a good look at the tree and the butt of the tree, I noticed that the normal flaring of the trunk at ground level was not happening; this instantly tells me that the tree has been overplanted. In this instance, erosion was causing banking of soil against the tree trunk and was starting to cause collar rot. I removed the offending soil; I now continue to keep an eye on it, as the tree was planted too deeply in the first instance.
This tree is now thriving – the lichen has gone and the tree has a wonderful crop of ripening pears. Of course we get none of this fruit; the sulphur-crested cockatoos visit annually and they strip the tree. Any rotting debris at the base is soon found by our free-range chickens. Cohabiting at its best!