Mulching does a lot of great things for trees, gardens and landscapes in general. It retains moisture, blocks the growth of weeds, controls erosion and keeps soil temperatures stable. However, there can be too much of a good thing and that’s why mulch users need to be careful around trees.
At no time should mulch be left in physical contact with a tree. The reason is that the tree bark can be harmed by the high amount of moisture retained by the mulch. When touching, that moisture goes through the bark and into the flesh of the tree. This compromises the tissue of the tree and prevents nutrition from traveling from the top of the tree down to the roots. In turn, the roots will collect less water and will not be able to feed the tree adequately.
No layer of mulch, no matter how thin, should be left in contact with a tree. Young trees are especially vulnerable to direct contact with mulch.
To make matters worse, some inexperienced landscapers not only let mulch touch trees – they pile it on around the base, creating something commonly known as a “mulch volcano.” This mound of mulch encourages insects and other pests to enter the flesh of the tree and can actually block rainwater from getting to the roots.
If someone puts a mulch volcano on your property, pull it apart as soon as you can. Make sure both the trunk and the base of the roots are clear of mulch. Otherwise, your tree is doomed.