Iceland’s volcano and the havoc it’s ash created made world-wide news. However, each spring, on trees throughout NE Ohio, volcanoes erupt with little notice or fanfare. I’m talking about “mulch volcanoes” just like the one pictured above which I saw while driving on a client’s street.
“Isn’t mulch good for trees?” you ask. Well, yes a 2-3″ layer of mulch over the root zone of a tree provides many benefits. These include retention of soil moisture, moderation of soil temperatures, inhibition of weeds, and the enhancement of the soil biology.
However, excessive mulch holds moisture against the bark, which can eventually cause it to decay. Also, buried beneath all this mulch are deprived of oxygen. Another problem with excessive mulch is that it creates a safe haven for small animals such as mice to feed on the bark unseen until you notice dieback in the top of the tree.
When thick rings of mulch dry out completely during long periods of dry weather, they will tend to repel water. Rain that falls afterward may be lost to runoff rather than benefiting the affected tree.
Trees will tend to produce roots in the mulch. These are known as adventitious roots. They are not true roots since they are produced by stem tissue rather than root tissue, and are not capable of supporting the trees as their real root systems decline.
In addition, these adventitious roots frequently develop into “girdling” roots – roots that grow around, rather than out from the trunk, damaging tissue which translocates water & elements upwards from the soil and starches & sugars produced in the leaves down to the roots.
Remember, there should only be a 2-3″ layer of mulch. This will be sufficient to obtain the benefits of mulching without endangering the health of your trees. Over time, mulch may become matted together, so be sure to rake it out occasionally to break it up. Also, keep it several inches away from physical contact with the trunk.
Don’t let mulch volcanoes erupt on your trees this year!