Mulching Has Both Benefits and Drawbacks to Gardeners
Nature Notes
By Patricia Martin

To mulch, or not to mulch, that is the question. Well, at least that is one question. The question of mulching first came up early this summer. Without thinking much about it, I had always thought that mulch was a good thing for the garden, and whatever the hardware store or garden center sold was probably okay. Two different people asked me earlier this summer if mulching with cedar chips or bark was all right, or if it was harmful to the perennial plants in their garden. The question of mulching arose again when Jeff Young came here from Vermont to conduct the lilac talks and walks during the festival, and to help plant new lilacs in the marina area, and trim a couple of the old lilac pods in Marquette Park. In one of his lectures, he indicated that cedar bark mulch and/or cypress mulch are not good around trees, shrubs, and perennials. So what is the truth about mulching?

I headed to my gardening books and to the library in search for answers, and discovered that mulching, and which mulch to use, is a complicated and rather controversial subject. Who would have thought! I found whole books devoted to the subject, and even after reading them, I'm not sure that I'm that much clearer.

Let us start with the definition of mulch. As Stu Campbell writes in "The Mulch Book," "Ask 10 gardeners to define a word like mulch ... and you will get the proverbial 10 different answers." The best definition that I've found is that mulch can be any material applied to the surface of the soil to act as a barrier to retain moisture, to insulate and stabilize the soil, to protect plants, or to control weeds. Generally speaking, mulches should have a couple of properties. Whatever mulch that is chosen, it should be light and open enough to let air and water pass through, and it should be heavy enough to inhibit or choke off the growth of weeds.

In general, there are two types of mulch: Organic and inorganic. Organic mulches are those that are basically unfinished, unheated compost, and are often the most desirable, as they biodegrade and add nutrients to the soil, as well as mulch's other attributes. Inorganic mulches, also known as inert or artificial, have no plant material in their origins. They're things like plastic, minerals, and stones.

There are those gardeners who see more drawbacks than benefits to mulching. They admit that mulching will reduce, although not eliminate, weeds, and make those that do grow easier to remove, and evaporation is checked and soil is kept cooler, which means that earthworms stay near the surface (although it does not necessarily increase their numbers). The drawbacks are that if the mulch is coarse hay or other such materials, the moisture from light rain remains, and is held by the mulch, instead of passing into the ground. Cooling of the soil is not always beneficial to plants, particularly young seedlings, which need warm soil to sprout and grow. Another difficulty is that as organic material is broken down by microorganisms, whether in the soil or in the mulch, it takes nitrogen. The thought is that mulches could potentially rob nitrogen from the soil. In addition, if mulch is placed thickly around trees and shrubs, it may encourage mice and other rodents to take up residence and chew the bark of the trees and shrubs.

While all of these arguments have some validity, there are ways of getting the beneficial results of mulching, and at the same time, reducing the negative impacts through the selection of proper mulching materials, how and when mulch is laid, and how the garden is cultivated.

Mulch is not going to eliminate all of the gardening chores, but it can make them easier. While mulch won't eliminate all of the weeds, it will cut the numbers down, and you will just have to pull out the others. The inhibition of water penetration by mulch is greatly dependent on the mulch used. For instance, if you use black plastic, it will not let the rainwater into the soil, and therefore the roots, and the same thing can happen with organic mulch. If organic mulches get matted down, or if you use certain types of organic mulches that shed water and that are large (bark, wood chips, unchopped hay, etc.), water may run off and not soak through. If you use black plastic, water well first (it's a good idea to water well before putting down any kind of mulch), and cut X's at intervals in the plastic to let water in. If using organic mulch, use ones that are finer, that are smaller pieces, such as chopped hay or ground bark, instead of whole or merely shredded. The organic mulches can be lifted and loosened periodically. This also helps with air exchange. The other thing is to make sure the mulch is not too deep. Any fresh, light-colored, unweathered organic mulch will steal nitrogen away from the soil in the early stages of decomposition. Eventually, they will add nutrients back into the soil, but to deal with the initial shortage, you can add nitrogen in the form of cottonseed meal or alfalfa meal, or a chemical nitrogen source like calcium nitrate or urea.

Mulch can create an environment for growing insects, slugs, and snails. While most of the insects living in mulch don't cause trouble, in a wet spring, slugs and snails will love it. These can pose a problem, and can be caught in slug traps (beer in a tuna can), dusting wood ash or diatomaceous earth around the plants (these irritate slugs), or a commercial slug killer. If you're worried about rodents living in mulch, don't put mulch right up against your trees or shrubs. This means that if rodents are living in your mulch in the winter, they have to come out in the cold to eat your trees. You can also wrap your trees or shrubs with a wire shield around the base. With seedlings, it's often a good idea not to put mulch around them until they're well established. Some people don't like mulch because of its aesthetics. This is a personal preference, so individuals must choose the one they like best.

This is just the beginning of the information that's available regarding mulch, so next time I'll discuss types of mulch, what types are good under what circumstances, and all sorts of other mulch information.

P.S. While riding with friends in the woods Tuesday, July 15, near Soldier's Garden, we spotted the first Indian Pipe of the year, popping white out of the ground. This is the earliest I think that I've ever seen it on the Island. Has anyone had an earlier sighting?

Trish Martin is a yeararound resident of Mackinac Island, has earned a master's degree in botany from Central Michigan University, and owns Bogan Lane Inn.