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Is Your Mulch Magnificent? Or Miserable?
MakeSure that the mulch you choose helps your plants instead ofharming them!

Question. Dear Mike:  We haveused black shredded mulch in the flower and shrub garden in front ofour house for several years. After listening to a recent show, I'm nowwondering if it might be part of the reason many of our seedlings don'ttake and my wife's perennials don't come back. If the mulch is toblame, what are our alternatives for preventing weeds while alsodressing up the appearance of the front of our house?
                ---Michael in Mount Laurel, NJ.

Mike: What kind of mulch should I not use? The last 2 years I have usedLicorice Root type mulches, but now I have black spots on my patio thatlook like soot. And what can I
do to get the spots off? Thanks,
                   ---Anna Marie, a teacher in Cherry Hill, NJ

Answer. I have been warning peoplefor years that wood mulches—wood chips, shredded bark, sawdust, andthose increasingly popular 'root mulches'—can breed 'shotgun' or'artillery' fungi that shoot tar-like spores as far as 30 feet towardslight colored objects, like the side of your house or car. These sporescan be removed pretty quickly if you get to them right away, says Dr.Dan Herms from Ohio State University: Soak them thoroughly with soapywater for a few minutes to loosen the natural 'glue' they exude, thenscrub them off vigorously. But as we have always warned, once thespores dry they are virtually impossible to remove without destroyingthe surface they're adhering to.

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 inyour soil, a process known as "Nitrogen immobilization". Wood iscarbon; carbon always looks for nitrogen to bond with so it can breakdown into new soil—that's the principle behind composting. Wood mulchestake that nitrogen right out of the soil, out-competing yournitrogen-needy plants. And dyed mulches are the absolute WORSToffenders; the wood in these old pallets—chipped up and sprayed withdye—is the worst type for use around plants. Our favorite mulch expert,Ohio State Professor Emeritus Dr. Harry Hoitink, warns that dyed mulchis especially deadly when used around young plants or in brand newlandscapes.

There's also another problem that occurs around this time of year, whensap filled trees are chipped and shredded and the mulch sits around allpiled up. Dr. Hoitink explains that this sap becomes a high-strengthvinegar, with a pH as low as 2.5; no plant can survive such an acidicattack. So doubly beware of wood mulch with a sour, vinegary smell.
Heard enough bad things about wood mulches yet? (We'll post links toOhio State and Iowa State horticultural bulletins about these andothers dangers with this Q o' the week.)

So what SHOULD you use?  Our new mulch maven Dr. Herms (Harry isretired and wants to pass his well-mulched torch) warns against usingone of my old favorites, straw. He says that straw is carbon-richenough to cause some of the same plant-food stealing problems as wood,and that it often contains seed heads that can cause weed problems(which we've warned about in the past) AND attract rodents that willthen look for other trouble to get into on your landscape (which Ihadn't thought of before).

He does think highly of my personal mulch of choice, shredded Fallleaves—but doesn't think it's the absolute #1 choice. Both he and Harryfeel confident that, after many years of active research, they haveuncovered the BEST all-around mulching alternative.

You ready? It's compost.


You Bet Your Garden   Question of the Week ©2005 MikeMcGrath.