I am not sure how this got started, but I have an idea. You hear and read information about how detrimental it is to plant a tree too deep in the ground. Trees planted too deep wind up either dying or just sitting there not growing. To try to avoid this mistake, many times trees are planted a little higher to make sure the roots get plenty of oxygen. You should always see the bottom roots flair out on the tree trunk, ideally at ground level.
As a result, many landscapers are planting them high, and in many cases too high. Then when they apply a normal layer of mulch it just looks like a big pile when in fact it is not. So when trees are actually planted at soil grade, many landscapers and homeowners are copying this look by adding too much mulch.
Most gardeners know that mulch, particularly for young or newly planted trees, is good for the plants. It provides them with a constant supply of oxygen, keeps the soil at a more even temperature, helps prevent weed growth, conserves moisture, over time adds organic matter to the soil, reduces soil erosion, and adds value to the landscape property. Sometimes even more important than all those things is mulch keeps weed eaters and lawn mowers away from the trunk.
The proper way to mulch a tree or shrub after planting them at the proper depth is to apply about 2 to 4 inches (3 to 5 with pines straw is fine) over the entire root system of the plant. But while doing this, you should keep the mulch a few inches from the base of the trunk. Remember, you should be able to see the root flare at the bottom of the trunk. If you can see the trunk but no flare, then the tree has been planted too deep and that is another subject for another column and not a good thing. If you already have too much mulch and have it up against the trunk, just pull it away and use the extra somewhere else.
But volcano mulching is not good for those young trees and can have a detrimental effect. It can invite all kinds of problems such as insects, disease, fungi, and small rodents.
Tall, cone-shaped mulches can actually “shed” water in much the same way an umbrella keeps the user dry. The surface of mulch quickly dries, inhibiting the passage of water. When the mulch is domed up, water simply runs off and ends up well outside the limited range of the roots.
Another problem with volcano mulching is newly developing feeder roots will actually grow into the mulch layer rather than down in to the soil since they can be deprived of oxygen. By growing into the mulch, the roots are in much more need of water and are more susceptible to extremes in weather conditions be it drought or heat during the summer, or cold during the winter. Add to that, if you have weeds come up and decide to spray them with glyphosate (Roundup), glyphosate breaks down in the soil but not in mulch so you can wind up damaging those feeder roots.
The volcano mulch is also a haven for small rodents, namely mice and voles. They will chew on the bark and that can mean no sap movement or nutrients to the upper branches.
Finally, the volcano mulches keep the bark moist on the trunk virtually all the time and this can set up perfect conditions for the formation and growth of fungal cankers or other tree bark diseases. It may also increase the likelihood of borers.
When it comes to mulching a young tree, think about how Mother Nature, in her infinite wisdom, does it. Leaves naturally fall from the tree in more or less an even layer; they rarely form deep mounds at the base of the trees. Those few inches of fallen leaves slowly decay, eventually becoming an important element in the long-term nutrition of the soil those trees live in. Mother Nature never creates mulch volcanoes around trees. And we know how rapidly most of the trees in the forest grow, and generally, how healthy, durable, and insect and disease free they are.
The next time you purchase and plant an expensive tree, do the right thing by applying mulch properly. Lay down a flat, or only slightly mounded 2 to 4 inch layer of organic mulch. It doesn’t matter which one – pine straw, pine bark, cypress, etc., that is up to you. Then make sure the tree gets a good soaking when it gets watered. Your tree will wind up doing a whole lot better than on of those stressed out trees erupting from a mulch volcano.
Reach Sid Mullis, the director of the University of Georgia Extension Service office for Richmond County, at (706) 821-2349 or firstname.lastname@example.org.