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Q. Hello Mike! I live near Annapolis, but visit Philadelphia often and listen to your Public Radio show when I’m up there. I live in a townhouse. When I put gardens in the front and back yards, I purchased many bags of mulch from the local home store. Now I need some more, and have since learned that I can get it from the township instead—but I have also heard this would be a terrible thing to do because it has not been treated for termites.  
Is it true that I should not use the mulch from the county? They make it from trees they’ve cut on the roadside. Is the mulch I bought any different from the county stuff?  If so, can I treat the mulch from the county? If it makes any difference I have very wet, clay soil.  I have been adding peat moss and soil conditioner to the gardens.
                                Thank you for your time and a great show!
                                --Elizabeth; Crofton, MD

A. Well, thank you, Elizabeth!
Now, first things first—I have no idea what the “soil conditioner” you’re adding might be, but I strongly suggest you ask your local County Extension Agent about the wisdom of doing so before you use any more of it. And don’t use any more peat moss—it will NOT improve your clay soil, but it WILL greatly change that soil’s pH, perhaps enough to make it very unfriendly to many plants. (Peat moss is best used to lower the soil pH for acid-loving plants like azaleas and blueberries, and to create lightweight potting and seed-starting mixtures—it is not an all-purpose soil amendment.)
After decades of battling the lousy stuff personally, I’ve come to realize that the only real way to ‘improve’ heavy clay soil is to dig it up, throw it away and replace it with a nice mix of something like half screened topsoil and half compost or mushroom soil.
Now, on to your mulch issues. First, as I trust you’ve noted from previous shows, wood mulches can be a bad idea for reasons other than infesting insects. In fact, I’d worry much more about the possibility of shotgun fungus staining my house and car than about termites moving in. But let’s discuss mulches and termites in some depth anyway—with Bill Quarles, Director of the BIRC, an organization that helps homeowners and professionals find the lowest-toxicity remedies for pest problems. (They publish two journals—The IPM Practitioner and Common Sense Pest Control Quarterly.)

Before I spoke with Bill, I believed, like you, that wood mulches had to attract the little buggers to framing—which they do, but it turns out so does just about any mulch. Bill explained that researchers at the University of Maryland recently found that termites don’t care about ‘content’—they just want cover, and even gravel and stone mulches help them greatly to reach their goal. That’s because, in this part of the country, the only type we have is the subterranean termite; so called because they must stay under ground or other cover to survive. (The ‘mud tubes’ [upright tunnels] they build on stone walls and such to provide cover when they have to leave the ground to reach wood framing are often the first clue that they’ve entered a home.)

ANY mulch provides the cover they require to approach a home. Yes, wood ones also provide food, but that’s not as much of an issue as we might have thought, explained Bill-- there’s generally lots of food in the ground for them. What they NEED is something cool and moist to cover the soil they travel under—mulch. So while mulching does keep moisture in the soil, prevent weeds, etc., it also creates a highway leading termites to your home—which having bare ground (again, a bad idea horticulturally) would avoid.

But don’t everybody go pulling up your mulches. Considering that they are literally everywhere in our environment (if you dig in 100 people’s yards in the United States, you’ll find termites in the vast majority of the samples), they don’t really to seem to attack homes all that often. Bill feels that, thanks to the abundance of woody food in the wild, they don’t need to.
But, of course, they sometimes do—and statistics don’t count for much when its your home being munched. The best way to protect a home against this possibility is with bait stations: Metal or plastic devices that you (or a pest control specialist) half bury in the ground in a perimeter around your home. They have a lid you can lift aboveground, and holes for the termites to enter the stations below ground. You put some bait wood (generally pine—their favorite) into the stations and check them monthly. If and when you see termites feeding on the bait, you replace it with wood treated with something that will wipe them out.
The best choices are an insect growth regulator or a boric acid solution—both are low toxicity to humans, and they’re taken back to the nest by workers, where they eventually kill the queen, thus neutralizing the whole colony. All without any spraying of the structure itself or exposure of toxins to the environment.

It’s doubtful that your original mulch was treated with anything—by law it would have said so clearly on the label. But there IS such a product--a boric acid treated wood mulch called “Term-A-Rid” that’s available at local landscape suppliers and garden centers. If you decide to go this route, test some in a small, planted area first—there were reports that it damaged some plantings a few years ago. (Boric acid is a form of boron—which in low amounts is a vital plant nutrient, but in larger amounts a plant killer.)

©2004 Mike McGrath

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