Proper Mulching Around Trees

Avoid “Volcano” Mulch Around Trees

Brian Jervis: Ask A Master Gardener

Sunday, November 24, 2019

Q: As I drive around town, I see small trees and crape myrtles with very large mounds of mulch, kind of like a pyramid. Is that the right way to do it? VM

A: Master Gardeners call that a “volcano” of mulch and the No. 1 rule in the mulching handbook says, “just say no to the volcano.” More on the volcano later.

In reality, mulching your plants, trees, and shrubs (properly), is one of the best things you can do to contribute to their long-term success. Here’s why:

Mulch greatly diminishes the quantity of weeds. The protective barrier that mulch provides not only stops migrating weed seeds from making contact with the soil to take root, but also provides a barrier that diminishes the ability of emerging weeds to grow. Fewer weeds means more nutrients and water available for your plants. A good layer of mulch also reduces the time you need to spend on your knees pulling weeds.

Mulch helps regulate soil temperature. During the height of summer, exposed soil here in Oklahoma can vary by up to 40 degrees in a single day, with soil temperatures reaching almost 120 degrees at a 1” depth. When you use mulch, that daily temperature variant is reduced to only about 10 degrees. This provides a much healthier growing environment for your plants.

Mulch helps with water management. As you might imagine with the extreme soil temperatures of un-mulched soil, water management easily becomes a challenge. High soil temps cause the water to evaporate quickly. This increases the need for water, which directly corresponds to the amount of time you need to spend watering. In addition, more time watering typically equates to an increase in your monthly water bill.

Even in the winter, mulch can help retain moisture and protect your plants from cold winter extremes, decreasing the chances of those tender perennials freezing out.

There are a variety of mulch types you can use in your garden: wood chips, sawdust, straw, and even mulched leaves. As we are in the season where the leaves are falling or have already fallen, mulched leaves make a great garden mulch. You can run your leaves through a relatively inexpensive leaf mulcher or pile them in the driveway and let your lawn mower do the work.

After mulching, just bag them up, store them in an out-of-the-way place and next spring you will have your garden mulch ready to go. This also helps add organic matter back into the soil; something most every garden in NE Oklahoma will appreciate.

Now, back to the volcano. The main problem with mulch volcanos is that they are piled up around the trunk of the shrub or tree. As we have mentioned, mulch helps retain moisture and piling mulch against the trunks helps keep them moist, which contributes to disease and bark degradation … ultimately shortening the life of these plants. Mulching around trees and shrubs is great, just keep the mulch a few inches away from their trunks.

Remember, just say no to the mulch volcano!

Garden tips

·        Apply dormant oil for scale infested trees and shrubs before temperatures fall below 40 degrees Fahrenheit. This would include crape myrtles infected with crape myrtle bark scale. Follow label directions.

·        Continue to plant balled and burlapped trees.

·        Wrap young, thin-barked trees with a commercial protective material to prevent southwest tree injury.