How Much Mulch Is the Right Amount?
Let's begin with the fact that everything is relative. I live in a county that experiences quite a bit of rainfall.
- More than 50% of Transylvania County is covered by three parklands: Pisgah National Forest, DuPont State Forest and Gorges State Park
- Transylvania County is home to over 250 waterfalls
- Transylvania County has the highest rainfall of any county east of the Rocky Mountains
- Transylvania County has the best water quality in the State of North Carolina
- A portion of Pisgah National Forest is considered a rainforest due to its high annual precipitation levels
Which means that what my garden needs is a little different from that of my relatives in southern Arizona.
A couple of days ago I blogged on the heresy of
plaguing my little piece of heaven. While my poor mother is bemoaning the lack of precipitation in her home state, I'm enjoying regular intervals of the wet stuff. So my mulch needs and issues are going to be different than hers. Or my sister's. Or my aunt's. All of that moisture creates a home microclimate much more conducive to molds, mosses and mushrooms. And perhaps wax scale. But I digress.
A typical recommendation for mulch depth is three inches. In a dry climate, that mulch can be a bit closer to the trunk of the plant than I can get away with here. This illustrates, however, two of the big mistakes people make with mulch. One, piling it too close. Two, failing to supervise.
I bet you can think of a yard near you in which the mulch is piled in ...er... piles around the trunks of trees. This is a common practice, but that doesn't mean that it's a smart practice. Accumulated mulch next to the trunks or stems of plants (even those as large as trees) creates a little haven for all sorts of naughty critters that love to chew on them. Or grow in the niches. Bark on a tree (or shrub) stops at ground level. It is, essentially, the skin of the plant. Now. Imagine that you have a band-aid on one of your fingers that gets wet. If you live where I live, that band-aid is likely to stay kind of wet. If you live in the desert, it should have a chance to dry out. But if I've got a soggy band-aid over my finger for say, months at a time, how long does it go before the skin starts to slough off? This is the problem with mulch directly against the bark of a tree or shrub. The poor thing needs to breath to protect its skin.
Even when there are not regular intervals of moisture, mulch against a trunk can provide cover for larger, bark-chewing insects and rodents. Any of these guys can cause disease or death of your plants. So even in drier climates, it is best to keep mulch away from the stems. Keep the mulch just barely covering the soil until you get beyond the stem and work your way up to the three inches that is the standard for mulch. The functions of the mulch are to choke out weeds, provide cover for soil enriching insects and to regulate soil moisture. Missing a few inches around the base of your plants won't hurt. And in densely planted beds, eventually it gets to the point where you need very little mulch at all--as long as you don't strip out all of the leaves shed by leaves in fall. (
Photo at left: shredded bark mulch at the NC Arboretum.
One of the more fun parts (to me) of gardening is observation. Walking around and seeing what is happening with your plants and the critters making use of your plants is not only satisfying, its entertaining. Until, of course, you find wax scale on your hollies. But even that can be satisfying in a perverse sort of way as you annihilate the threat. In this particular case, the perceived threat alerted me to something I should have noticed sooner--the need to pull back the mulch from the base of my holly shrubs. Those who may have to rely on outside help in keeping up their yards can be especially vulnerable to mulching mistakes like those described here because sometimes a) the ones they hire don't follow instructions or b) they believe what they are told by landscapers who really don't understand the threat. Or who wish to be hired to spray pesticides. Maybe I'm being a bit cynical there, but you know what I mean.
While stone or brick nuggets or other long-lived mulches will help to suppress weeds, organic mulches are the way to go. "Organic" in this instance doesn't just mean a natural product (because of course stones are natural, too), but a product that will break down over time to enrich the soil. For those concerned about the threat of termites to structures, you may choose to use an inorganic next to your home's foundation and then use your organic mulch elsewhere in the yard.
into termites and mulches shows that while yes, termites will eat mulch, it can't be proven that they are more likely to eat a house with mulch at the foundation. A summary of the research makes the case that the benefits of organic mulches outweigh the risks--just be vigilant!