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Using Mulch Wisely

Question. Mike: I've been vegetable gardening for over 10 years and have always relied on chemical fertilizers. Even worse, I'm guilty of using your least favorite weed control product: Roundup. But this year marks a new chapter as I attempt my first organic garden. The issue is mulch. I have read your articles and realize that wood mulches are a no-no. (Just in time; I was going to pick up a load of red wood mulch this weekend!) I do plan on starting a compost pile when the leaves come down this fall, but this year I'm out of luck. How do you feel about using grass clippings as mulch? My tomatoes, squash, cucumbers, and green beans have all been fertilized naturally and look happy & healthy, but the weeds are beginning to get unruly. I need help quick!

---"An old dog trying a new trick", Trey in Jerseyville, IL (1 hr. north of St. Louis)

Answer. Welcome to the fold, Trey; we forgive all sinners! (Unless they keep killing frogs and toads with Roundup, then we hurl slugs at them.)

You have named an excellent mulch—when used correctly. In weed control studies at The Rodale Institute in the '90s, DRIED grass clippings outperformed all other mulches, even black plastic. But dried they must be; wet clippings mat down into a slimy mess. So get those clips out of the collection bag right away and spread them against a fence or anywhere they'll get lots of airflow. The thinner you spread, the faster they'll dry. When their bright green color turns tan, they're safe to use. The lawn should be bone dry when you cut (which it should ALWAYS be anyway, as cutting wet grass makes for a lousy looking lawn). Add in some bright sun, a light breeze, a couple of passes with a rake and those clips could be ready in 24 hours.

Now the caveats:

  • Do NOT use clippings from lawns that have been treated with chemical 'weed and feed'. If that's all you have access to, mulch with compost this season, sin no more and use clean clips next year.
  • Never pile ANY mulch higher than an inch or two.
  • Don't touch the plant with any kind of mulch; always leave a few inches open all around the stem or the trunk
  • And mulch at the same time you plant. Otherwise, we hear, those weeds can get downright unruly….
Question. I have heard you warn not to use wood mulch for years, but was always too lazy to try and find compost for my landscaping. Then our house was attacked by those horrible tar-like spores last year and I am now determined to really listen to you and never use wood mulch again! The problem is that I can't find "landscape compost" anywhere; only leaf-mulch compost. I did find a place that will deliver it, but the man working there told me it wasn't as effective as wood mulch at holding down weeds. Is he correct? I need to act on this soon; the weeds are having a blast in my beds! Thank you!!

---Anne, near Doylestown, PA

Answer. Thank you, Anne! Our in-box is FILLED with messages from people who ignored our wood mulch warnings and woke up to find their home and/or cars covered with those impossible-to-remove artillery fungus spores. (Details & pictures at this fine Ohio State Extension Bulletin) Every Spring we select a new tale of wood mulch woe to try and warn other compulsive mulchers, and you're this year's "loser"!

By the way; in addition to staining homes and cars, killing plants and feeding termites, we've seen disturbing news reports recently about house fires starting in wood mulches. In some cases, the cause seems to be spontaneous combustion, a direct result of this hideous trend of so-called "decorative mulching", where people buy chipped up trash wood that's been spray painted an unnatural color and then pile it so deeply it reaches critical mass and bursts into flame. So be thankful you still HAVE a house!


Here's the facts: Two inches of yard waste compost prevented weeds just as well as two inches of ground wood mulch in an intensive study performed by researchers from Ohio State University, Iowa State University and the University of Kentucky.

AND those researchers and others I consulted while writing my recent book "Mike McGrath's Book of Compost" (published by Sterling last Fall) felt that mixed yard waste "leaf compost" was the absolute best kind! So mulch away, Anne! (Just remember—even with compost: Not too deep; don't touch plants…)

Question. Dear Mike: I have some tomatoes and peppers in pots. What kind of mulch can I put on them? This time of year I don't have any source for leaves. Thank you,

---James in Prattville, Alabama; where we love your program on 89.9 FM out of Montgomery

Answer. Thanks, James—we loves our Southern listeners! Now, you're in steamy Zone 8, where organic matter cooks out of the soil super fast. So, while I would tell my Northern container gardening neighbors to apply an inch of compost on top of their soil-free mix and then freshen it up once about halfway through the summer, I recommend that you find a nice supply of a high-quality bagged compost (NOT composted manure), apply an inch on top right away and then a fresh inch to the surface of your containers every month. This will retain moisture, prevent weeds, feed your plants, leap tall buildings in a single bound…

The basic idea is the same for regular old in-ground mulching in the steamy South; start with two inches of compost or shredded leaves and then add a fresh inch every two months during the growing season to keep your plants happy, health and weed-free.


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