Thursday, June 17, 2010


I'm a little worried. There is a volcano just down the street from where I'm sitting.

Are you picturing an opening in the crust spewing lava or a too high mound of moisture-rich mulch? Both are hazardous, the latter is completely avoidable.

When mulch is pushed up along the sides of a tree trunk, it is referred to as "volcano mulching". Some people think this is attractive and mistakenly believe it helps trees establish themselves after being planted.

Mulching IS great for trees but only when done properly. Mulch conserves soil moisture, moderates soil temperature and reduces competition from roots of weeds.

Volcano mulching can lead to fatal consequences for a tree. Here are three reasons why you should abandon creating a reproduction of Mount Vesuvius at the base of your trees.

Bark decay - Mulch holds moisture but when it is stacked up against the trunk of a tree it can create conditions where the bark begins to decay. This allows openings for pests, fungi, bacteria and insects to get under the bark and cause internal problems.

Girdling - Tree roots naturally grow outwards. Layers of moist mulch can be too tempting for trees to resist and their roots will grow up into the mulch. Since most volcano mulching is circular, the roots try to stay in this moist environment by circling itself. This circling reduces the span of the root structure preventing the tree from accessing water and threatening its overall stability.

Branch die back - Some mulch (hardwood bark) releases the metallic element manganese into the soil when it decays. After repeated applications, the level of manganese can reach a point to where it starts to rob the tree of the iron it needs. In the end you get smaller leaves, leaf yellowing and branch dieback.

As I said, mulching is great for trees when done properly. Apply mulch using the 3-3-3- rule and your leaf and needle friends will thank you with cooling shade during the summer.

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