Mulching Your Tree

People mulching a tree

Arguably there is nothing you can do for your tree that is more beneficial than mulch. Proper mulching helps your tree get enough water during dry summer months, keeps away grass and weeds that compete with your tree, protects your tree from damage by lawn mowers and weed whackers, and breaks down slowly over time feed your tree. It’s a simple way to keep your trees healthy and to give your yard a well-cared for look.

What type of mulch should I use for my trees?

Technically, mulch can refer to any type of non-living ground cover. When arborists talk about mulch, what we really mean is wood chips. There are a few types of wood chips, and some are better than others.

Arborist wood chips are the best for mulching trees and shrubs. Arborist wood chips are ground up when older trees are pruned or removed. They include both green parts (leaves) and brown (woody) parts. They have some large and some small pieces. The mix of green and brown is a great combination, as the green will break down quickly to add nutrients to the soil immediately, leaving behind the brown woody parts which will break down more slowly over 1-3 years.

Studies have shown that arborist wood chips outperform other landscape mulches, including beauty bark, in moisture retention, temperature moderation, and weed control. Wood chips break down slowly, supplying nutrients to the soil longer than beauty bark.  Arborist wood chips have also been found to be the most effective mulch for enhancing plant productivity and keeping urban trees healthy.

Large wood chips are more uniform in nature and do not contain any green (leaf) material. These chips have been processed and do not come directly from the wood chipper. However, because they are large in size (ideally at least an inch long) they shouldn't break down too quickly and will still help prevent weeds and hold in water. These are ok for your tree if you cannot get arborist wood chips.

Beauty bark is woody material that is very small, uniform, and contains no green (leaf) parts. Beauty bark breaks down very quickly, meaning it must be replaced often. Some beauty bark is dyed (red is common). This dye is not something you want in your soil or local water ways - which is where the dye will go as the bark quickly breaks down. Do not use beauty bark around your tree.

Compost is not a woody mulch material and should not be used as such. Compost is more similar to dirt. It will not keep out weeds or hold moisture in the soil the way wood mulch does. You can used compost around trees as a thin layer applied on top or just below wood mulch. Do not mix compost into a planting hole. Compost is very beneficial in other areas of your yard, but use sparingly around trees.

Where can I get mulch?

While arborist wood chips are best for your tree, they can be hard to get especially in the small quantities you need to mulch just one or two trees. The best way to get arborist wood chips is to contact a local arborist and ask them. Most arborists will dump a load of chips at your home for low or no cost. Keep in mind that the amounts they will deliver vary, and are usually between 4 to 12 yards. The good news is that you can use these in many parts of your yard, not just around your trees. And sharing chips with neighbors is great way to build community.

When working with an arborist to get wood chips, make sure you ask for "clean" chips. This means that the wood chips do not contain any invasive species such as ivy, holly, or laurel. If wood chips from these species are spread in your yard you could be introducing a very unwanted new plant.

Large wood chips can be found at a few hardware stores and nurseries in the area and is sold by the bag. One bag is usually appropriate for a tree planted less than 5 years ago; a larger tree may require more. When buying mulch from hardware stores and nurseries, make sure it is large sized chips (at least 1 inch) and is not dyed. Not all hardware stores and nurseries carry this kind of mulch; fine grained beauty bark is more common.

How do I mulch a tree correctly?

Spread mulch in a 2-4 inch thick layer around the base of your tree. Keep the mulch in a doughnut shape by staying a hands-width away from the truck. Mulch that is touching the trunk leads to decay which over time can kill your tree and cause it to fall from the base.

What is a mulch volcano and why is it bad?

Mulch volcanos are excessive piles of mulch piled high around the base and trunk of a tree. You see it often in commercial landscapes, but it should not be repeated in your yard! Piling mulch against the trunk of a tree leads to a host of problems including disease and rot.

Why should I weed the grass from around the base of trees?

Weeding the grass from around the base of your tree is a simple way to keep a tree healthy and protect it from weed whacker damage. Grass competes with trees, absorbing water and nutrients from the soil. Once you’ve removed the grass, lay down a 2 to 4 inch layer of mulch to retain soil moisture, control weeds, and insulate the soil from extreme summer and winter temperatures.

Watch this short video to learn more about how to properly apply mulch around your young trees.

Additional Resources