Urban settings can be a harsh environment. Large fluctuations in temperature, poor soil, and little organic matter are hard on trees at the best of times. Compound that with the way that they generally only experience moisture from short downpours that are quickly carried away by storm drains, and you have a very stressful environment for a tree, one that by no means contributes to the health or longevity of the trees.
However, there is one thing that is demonstrable good for trees in nearly any condition: mulch.
Why Mulch Helps Trees
Lets take a look at why mulch is so beneficial. What are the problems the tree faces?
- Extreme fluctuations in temperature. There’s no way to put a blanket on the whole tree, but the roots are more subject to the stress of temperature fluctuations anyway. A layer of mulch creates an insulating layer to reduce those fluctuations.
- Little organic matter in the soil. Although a little compost underneath is the ideal answer to this problem, mulch will eventually break down into compost, and will eventually mix with the existing soil.
- Poor soil. Poor soil often has little organic matter in the soil, but that’s not all — it often even lacks the microorganisms that break down organic matter so that the roots can absorb their nutrients. Though, again, compost is the ideal solution, mulch, particularly the double-shredded, aged varieties, will come with their own complement of microorganisms to help you feed the soil.
- “Flood or drought” cycle when it comes to moisture. Trees do not like deluges. There is a limit to how fast their roots can absorb water. A two-hour afternoon rainstorm like we are accustomed to in Northern Virginia will do very little for a tree, unless there is some way for it to trap water to absorb over time. Good soil will do this naturally, but as we have already established, many trees do not have good soil. So mulch, which is naturally absorbent, will have to do in a pinch.
Now that you’ve seen what mulch does for a tree, you will be better positioned to understand the best practices of mulching.
- Do use a double-shredded mulch when possible. It breaks down faster, but most trees can use the nutrients.
- Don’t spread the mulch too thickly. Most tree roots are within an inch or two of the surface, and they need a little bit of air. 2-4 inches deep is all you need.
- Do spread mulch out to the dripline, or further, if possible. This reduces competition from grass or weeds, and allows the mulch to hold a reservoir of moisture above most of the root structure.
- Don’t do a “mulch volcano.” Mulch holds moisture, and moisture against the bark encourages rot. Pull the mulch several inches back from the truck so that all the bark and the top of the root ball is exposed to the air.
With diligent applications of mulch every spring or fall, your trees will be the healthiest specimens around, with rich, fluffy soil and plenty of moisture.