Just when you think you have nothing more to worry about, “artillery” or “shotgun” mulch sends a salvo against your house. This was a mystery until scientists tracked it down. Folks reported sudden outbreaks of nasty little black specks on their windows and siding. Many thought it was tar. They were almost impossible to remove and left a black stain.
Just when you think you have nothing more to worry about, “artillery” or “shotgun” mulch sends a salvo against your house.
This was a mystery until scientists tracked it down. Folks reported sudden outbreaks of nasty little black specks on their windows and siding. Many thought it was tar. They were almost impossible to remove and left a black stain.
Pity the folks who parked their car near this mess. One company reported more than 100 cars damaged in their parking lot.
The culprit is a common fungus that grows in decomposing mulch. Its method of procreation is to shoot sticky fungal spores in every direction, some reaching 6 feet from the mother germ. Hence the name “artillery mulch.”
I talked to some mulch guys about this. “Some customers were blaming the chemical additives,” said one. “Researchers have found it’s a natural thing.”
Translation: It’s not our fault.
So what to do? Science is stymied here. There’s no cure for “artillery mulch.” The more mulch you put down, the better your chances of seeing it. There’s no fungicide that kills it. Anything that would murder it also would take out your plants.
Horticulturists suggest mulching every other year. The fungus seems to appear in new mulch.
The fungus itself is harmless, minus its explosive effects. Since there is no eradication, our efforts turn to prevention. Here we have some hope.
If you cover the mulch, you stop the firing. Some gardeners suggest 3 inches of mushroom compost, available by the bag at some garden stores. Their experience is it halts the action, but then the compost decomposes and the problem returns.
Shredded leaves are similar to compost. They too will decompose but more slowly. Once the cold weather takes hold, the fungi hibernate.
Another fix that really isn’t is to spread fresh, hardwood chips over your offending mulch. The problem here is fresh chips give off methanol gas as they rot. It is harmful to plants.
One disgusted gardener installed agricultural fabric over his mulch. That stopped the shelling, but it looks strange. The fabric lets light and water in and is available in stores under various names.
And now for the cleanup. Folks tell me they’ve experimented with all manner of detergents to no effect. If you can remove the spots by scraping, a stain will remain.
I had some on my basement windows. I sprayed them with the hose and waited a few minutes for the fungus to absorb the water. Then I scraped it off with a putty knife. It still was a tough job.
I was careful to collect the spores on paper towels. Letting them drop would only repeat the problem, as they are alive.
The worst is fungus on wood or vinyl siding. Here, scraping would cause damage. Until somebody comes up with an effective cleaner, you may have to live with it.
Power washing can be effective on new vinyl siding. The older siding has lost its oily sheen and is as bad as wood for sticking.
Painting over the spores will disguise them, but you will have a rough surface.
All fungi need humidity and warm nights to procreate. Excessive evening watering will promote them. Expect outbreaks after major periods of spring and summer rains.
Removing the infected mulch is an option. Bag it and send it to the landfill. Composting it will just spread the problem.
Some mulches are less likely to develop the fungus. These are ones that shed water. Pine bark nuggets and shredded cypress are two. Still, all mulch is susceptible, as it eventually will rot.
Jim Hillibish writes for The Repository in Canton, Ohio. Contact him at firstname.lastname@example.org.