Gas stations, supermarkets and discount stores are surrounded by walls of mulch, as well as the garden centers where one would expect to find this product, so it is probably time to write about the uses of mulch.
When used properly, mulches benefit plant growth and minimize labor. Their primary functions are the conservation of soil moisture and the moderation of soil temperature. Heat generated during the day is absorbed by the mulch and radiated to the soil at night when the air is cooler, and direct sunlight is blocked from the soil surface during excessively hot weather.
Mulches also block evaporation of moisture from the soil, slowing down drying, and help to prevent runoff from heavy rains, decrease erosion of soil and keep rain from pitting the soil surface.
In scientific horticultural discourses on mulching, you will not find appearance mentioned very often, if at all. I suspect though, more people purchase those bags of mulch to make their flower beds more attractive than those who buy them for conservation purposes. And this is fine.
Every couple of years, I seek out cocoa shell mulch for its chocolate scent and its nice appearance. This mulch is harmful to domestic animals if they eat it, but my dogs are on a leash when they are outside and do not seem interested in the smell of chocolate.
I am, though, and this product smells heavenly when you first put it down, and then has a new burst of scent after rain. It is made from the ground-up shells of the cocoa bean.
Many substances, organic and inorganic, can be used to top a garden bed.
The inorganic include stone, gravel, lava rock and such materials as recycled rubber. This type of mulch has the added advantage of extending the growing season by retaining heat.
Of course, in a hot summer, this also may be a disadvantage.
Organic mulches come from many sources, including wood chips, bark from softwood and hardwood trees, pine needles and compost. You also can use fallen leaves, although they are apt to blow around in winter wind and pass on the favor to your neighbors, who may not be properly grateful.
Using too much mulch can be harmful.
The "3 inches is good, so 6 inches must be twice as good" theory does not apply. On wet soil, too much mulch can stress the root zone and cause root rot. Using improper materials such as grass clippings can affect soil pH and lead to nutrition deficiencies, and mulch piled around a tree trunk in a volcano-like form could attract termites or rodents.
Before applying anything on top of the soil, check that soil drainage is adequate and will be maintained. If you use pine needles or bark, be aware this will acidify the soil to some extent.
A good depth to apply would be 2-4 inches, slightly deeper with coarse materials.
After several years of laying around without being disturbed, sometimes a toxicity will develop and cause an unpleasant odor, reminiscent of vinegar, ammonia or silage.
This happens because of a build-up of nitrogen, causing increased decomposition.
Low-growing plants in close contact with the offending substance are most likely to be affected, and plant kill may occur. If mulch smells unpleasant at all, either remove and replace it, or at least water plentifully.
So mulch on; just use care in selecting and applying and please - please! - don't use that awful red stuff if you live near me.
Janet Del Turco is a local gardener and a graduate of the Ohio State University Master Gardener program. Contact her at firstname.lastname@example.org.