Cones of Concern

I bet worrying about volcanoes is low on your priority list.  Well, I hate to tell you, but there are two types of local volcanoes to fret over.  The first is a “large swelling of hot rock” that Rutgers University scientists found deep below New England.  That magma isn’t expected to cause us a problem for millions of years, or perhaps ever.  The other type are in commercial landscapes, in front of convenience stores, and even in front yards.  They don’t spit steam and lava, but they’re dangerous nonetheless.  They are the MULCH volcanoes.

In case you think I’m blowing smoke, let me explain.  Over the last few decades, it has become a common practice to make a circle of mulch around a tree.  Sometimes, mulch is applied to the circle every year, and it eventually builds up ten, twelve, perhaps even eighteen inches high.  This “volcano” makes the tree look like it is sticking out of a highly iced cupcake (but we don’t call them mulch cupcakes because that would be, frankly, silly).

Stuff happens inside the volcano.  Surface rooting is encouraged, and girdling roots may grow around the trunk, strangling the tree.  Lots of organisms which decompose mulch accumulate, and they start to decompose the buried bark of the tree.  Insects and rodents may also be encouraged to move in.  If enough bark is destroyed, the tree declines from “mulch girdling.”  Lastly, some experts have found that hardwood bark mulch contains manganese.  More mulch means more manganese, which in turn robs the tree of iron.  Over-mulched trees may gradually have smaller leaves that are pale green or yellow, shoot dieback, and an overall unhealthy appearance.  

I’m not blowing my top over mulch around trees; far from it.  Mulch is good because it keeps mowers and string trimmers away, since dinging the bark enough times causes tree death from a syndrome called “lawn mower blight.”  Discouraging close grass and weed growth also provides a neat appearance and helps the tree to grow, since some herbaceous plants (such as the grasses called fescues) exude chemicals from their roots that actually inhibit young woody plants.  But we just need to layer the mulch two or three inches deep and no more, and to keep it away from the trunk.  Shape your mulch like a saucer, with a rim to catch water (especially for newly planted specimens) and very little in the center near the bark, and all will be fine.

So what started all this mulch madness?  Here’s my theory.  Unlike many horticultural problems which have their roots in neglect, mulch volcanoes originally sprouted in the well-tended landscapes around upscale apartments and commercial centers.  Each spring, the faded mulch was covered over with a fresh layer by busy landscape crews making things beautiful.  No one stopped to consider what was happening, and homeowners drove by, saw the highly manicured grounds, and said, “Hey, that must be the way to take care of trees!”  The volcanoes then went residential because people lava to mulch.