Mulch Volcanos or How Not to Plant Trees

It seems a lot of people and/or landscapers are under the misapprehension that when it comes to soil, more is better. This is not always the case.

This volcano of soil is doing a couple of bad things to this poor rhodo. Firstly, stems and trunks should never be buried like this. You’ll see more of this in the next few pics. You should always see the root flare at the junction between the stem/trunk and the soil. You’ll see “bell bottom trousers”.

Here’s a beautiful Blue Spruce in excellent condition

Secondly, rhodo roots are even more shallow than other woody plants, so adding ANY soil on top of the planting area is going to make your rhodo suffer–from too much moisture and too little oxygen.

You can and should still mulch rhodos, just several inches away the the trunk, and only about 2″ of nice light mulch (wood chips or well composted compost), not soil.

The Problem:

Exactly the same thing above–soil (or in this case bark mulch) mounded up around the trunks of these Thuja (arborvitae).  This causes a number of problems: Too much moisture against the trunk will invite disease and bark splitting. It also promotes root girdling, which is when roots start following a circular path around the trunk instead of heading out perpendicular to the trunk. As those roots grow and fatten they will often pinch the channels that draw water, oxygen, and nutrition up the tree. Root girdling is a very bad thing for your tree.

Two views of the same tree. Here the planter put a rodent guard around the base of the tree, which will also also help reduce moisture against the bark. But the roots will still opt to grow up into the volcano soil causing the root girdling again. And then to hide the look of the mounded soil, they planted creeping raspberry (Rubus pentalobus). In other circumstances I’d say this was a good plant for under the tree, but it will hold the soil there (eroding away would be a better thing) and act like living mulch, which will just exacerbate the moisture problem. (It’s a pretty vigorous plant in coastal BC and will begin to take over the lawn area–not a bad thing maybe.)

I plan to write discreet polite letters to the owners of these trees and shrubs offering to help remediate their plantings. Hopefully they won’t be too offended at the local busybody who thinks she knows everything!

Love to get your comments and questions.