Mulch without artillery fungus?

Asked August 30, 2016, 4:47 PM EDT

We put wood chips on a long retaining wall in the back. Unknowingly we ended up with dark spots all over the back of the house from artillery fungus in the wood chips. Ugh! I've removed 99.9% of the wood chips, have covered the area between plants with fabric to control weeds, but now want to put down some sort of mulch cover. I would like to use bark but can't find out if bark mulch or bark chips are as likely to contain the artillery fungus as the basic wood chips that we originally used. (It's a big area - 44' long x 6' wide.) Do you know?

Benton County Oregon

3 Responses

Hi there, thank you for using ask an expert. I have been researching your question and unfortunately there is not a wood product that has yet been found to be immune to this fungus. Cedar and cypress mulches are more resistant than other woods, with cypress being slightly better than cedar. There is some research that shows that bark products versus wood products have a lower incidence of this fungus but over time as they break down they also get infected with the fungus. A fungus requires moisture so our climate is perfect for growth during our rainy season. Larger pieces of bark nuggets allow the rain to penetrate through to the soil more readily than smaller nuggets which will soak up more the water as it passes through and therefore are more susceptible to developing the fungus. Studies show that the fungus is more of a problem during wet years and on the side of homes that are shaded and cooler. Light colored paints not only show the spots but also can attract the release of the spore packets that the fungus releases by mimicking the lighter colored sky. I do have some suggestions for you. One is use a stone such as pea gravel or other type of rock as a mulch. There are also shredded rubber mulches available made from recycled tires. If you want to continue using an organic mulch get a bark product without any wood mixed into it (this will be tough as most have some wood mixed in). Replenish the top 1- 1½ inches with fresh mulch every year. If you have plants in the bed, evaluate the irrigation method. You may want to change to emitters that water only at the base of the plants and not the entire bed, this would reduce the amount of moisture in the beds during our dry season and should reduce fungal population levels during the summer. Finally, you could consider planting grass or some other ground cover if the site is too shady for grass. Then there is the artificial turf option.....

Thanks for your reply. I could use a bit more input, please. I've been reconsidering all my groundcover options and am now wondering about using hazelnut shells. (I am shying away from pea gravel because the area is all brick and gets hot afternoon sun all summer long. I am also shying away from rubber options for the potential flammability factor - hubby is a forester and his first reaction was to be concerned if there was a fire. At some points the retaining wall is less than 6 feet from the house.) The retaining wall area to cover is 44' long and 6' wide. I have some cotoneaster in it with drip line watering, but that doesn't cover a whole lot of the ground. See attached photo. So, I thought of hazelnut shells. But I'm not sure about their potential for fire resistance, and I also can't find anyone who sells them in bulk. Thus, I don't even know how expensive they may be. Any ideas on where to find a lot of shells for a reasonable price? My last thought is just to plant some St. John's Wort around the cotoneaster (as I have that at the top level of the retaining wall) and hope it fills in as quickly as possible. I appreciate any thought you could offer! Thanks, Cindy

Thanks for your second question. As to the benefits and drawbacks of hazelnut shells, this is an informative article. The shells are available at some gardening/mulch/barkdust outlets.

Have you considered a native plant groundcover? Here's a link to an Extension article about them, and this is a great resource for native plants of all kinds. Plants appropriate for ground covering are on pages 21 and 22.

Good luck!