Avoiding Artillery Fungus and Plant Starvation by Using Compost as Mulch

Mike McGrath, the Garden Editor that you hear locally on WTOP FM, is also the host of the "You Bet Your Garden" public radio show. I came across a Q & A that he did a while back about using mulch, and I was really surprised by his take on it.

Having grown up in suburbia, I thought that a topdressing of wood mulch was just The Thing To Do every spring. But Mike argues against using wood mulch for two reasons: 1) mulch can "breed ‘shotgun’ or ‘artillery’ fungi that shoot tar-like spores as far as 30 feet towards light colored objects, like the side of your house or car," and 2) "wood mulches can also slow the growth of established plants—and yes, just plain starve new ones to death—by ‘tying up’ the available food in your soil, a process known as 'Nitrogen immobilization.'"

 Image of artillery fungus from bloominggarden.com

I found out about these fungi firsthand last year, when alien life forms that looked like hundreds of thumbtack-sized birds' nests appeared in my mulch, each "nest" laden with three or four tiny, hard, grey spores. Soon afterwards, a good fifteen feet or so of the privacy fence in my backyard was covered with these spores, which were just impossible to clean off.

  Image of spores on siding from bloominggarden.com

If you are attacked by shotgun or artillery fungi, Mike suggests dousing them with soapy water as soon as you notice the problem, then giving the whole area a good scrubbing to see if they'll pop off. Unfortunately, by the time you realize that you have a problem, the spores are usually well adhered, making them like the Gorilla glue of the fungal world.

 
So wood mulch kinda sucks, but you still need some sort of mulch if you want good weed control and moisture retention, coupled with the addition of delicious organic matter that your plants are craving for dinner. What are your choices?  Some of Mike's recommendations are straw and shredded fall leaves, but his top recommendation is ... drumroll please ... compost.

Image from frederickcountymd.gov

McGrath points to a study at Ohio State that showed that compost cut weeding time by 1/20th, the same result that researchers got with wood mulch. And in talking to one of the OSU researchers, a Dr. Herms, McGrath learned that "compost will also greatly limit disease and insect problems in the plants it mulches and improve their overall vigor and root growth; wood mulches ... often have the opposite effect." Bonus points: you don't have to apply additional fertilizer during the growing season if you've mulched with compost.    

Mulching with compost can be just as aesthetically pleasing as mulching with wood, as the above image (drool drool drool) from Bear Path Farm shows. So with this new knowledge in my toolkit, I began mulching my combo veg-and-flower beds with compost last week, setting aside the wood mulch I had already purchased to use as the base in my dogs' pen. (Hopefully they won't mind a ducking a few flying spores while they go about their business.) So tell me, have you ever heard about or encountered any problems with wood mulch? What do you use to dress up your garden beds?