Beware the Mulch Volcanoes! Tips for Successful Mulching
One of the first activities of spring gardening is mulching. The benefits of mulching are many. The most important is moisture retention in the soil, reducing the need for frequent watering during hot, dry spells. This is especially important when planting new shrubs and trees, even perennials and annuals. An additional benefit is keeping the soil
cooler in hot weather, reducing stress on both newly-planted and established plants of all sizes. Organic mulch (made from natural materials) breaks down to enrich the soil and feeds the plants it mulches.
There is a huge variety of mulching materials available on the market, both bagged
and bulk. That said, quality varies. Most any organic material can be used as mulch.
Bark (a byproduct of the lumber industry), ground up trees, utility crew trimmings,
lumber and wood pallets, leaves, and even grass clippings all can be used. Some
caution is needed though. When purchasing from reputable sources, there is not much
to be concerned with, but it’s always good to ask a few questions:
1. There is an important difference between “hardwood mulch” and “hardwood bark
mulch”. Hardwood mulch is made by chopping up entire trees, and is mostly wood pulp, in addition to the bark. Trees have bark to protect from insects, especially termites.
When using hardwood mulch, there is a possibility, although remote, of attracting
insects, including termites. In over 35 years of landscaping, I’ve seen just two cases of
termite infestations in hardwood mulch, but…
2. Exterminators always recommend that absolutely no organic mulch be used around
a home, but that is overkill. I’ve used hardwood bark mulch around my home on wooded
acreage for decades, with never a bug problem. Once, I even found termites in an old,
rotting wood pile just feet away from the house, but none living in the mulch.
3. Ground up wood pallets and other lumber (as well as the above-discussed hardwood
mulch) is great to use for paths and mulching areas away from the house, even
vegetable gardens. Just be certain that it is made from “clean” pallets that have not
been contaminated by chemicals or other toxic liquids.
4. Organic mulches should never be spread more than 4” thick. It will settle somewhat,
down to 3” or so, which should be good for at least a year. Any deeper will encourage
anaerobic mold, which is nasty.
5. Finally, some people and even poorly-trained landscape crews are guilty of creating
“mulch volcanoes” around trees, in addition to spreading mulch too deeply on landscape
beds. Mulch piled up around tree trunks causes bark rot, which leads to disease and
insect problems, and can actually kill even good-sized trees. Mice and voles use mulch
as cover over the winter to chew on tree bark. Correctly mulched, a 4” layer of mulch
should be spread with the mulch pulled away a few inches from the trunk of the tree,
forming a “doughnut” of mulch, NOT a volcano!