Dan Vierria: Do you compost? Grass clippings are great unless... By Dan Vierria -- Bee Columnist Published 2:15 am PST Saturday, December 10, 2005 Story appeared in Cal life section, Page CL5
Insecticide, herbicide and chemical fertilizers. A nasty concoction but that's what some homeowners are spreading on lawns for lush green, dandelion-killing, grub-whipping relief. Best looking lawn on the block. Yup, the stuff works.
But dumping treated lawn clippings on compost piles or spreading them as mulch around edibles - like a peach tree or strawberries - is asking for a heaping helping of toxic chemicals. Trust me, you do not want to sprout a third thumb or a tumor shaped like a zucchini.
No, I'm not one of those organic gardening champions who handpicks aphid and gasps at the mere mention of Roundup. Roundup is my friend, although we only hang out around ornamentals. I don't use Roundup near fruits and vegetables. Food is different.
Often readers will ask if they can compost a particular leftover.
"Oh sure, that's great for composting," I'll respond. "Do you also add lawn clippings?"
"Sure do!" comes the proud response.
"And you regularly spread turf-building products on your lawn?"
"Sure do!"
Let's face it, if you own a lawn spreader and use it often, the lawn becomes a mini toxic-dump site. That's why the Sacramento Waterwise Pest Control Program
If you must use turf builders, don't put clippings anywhere near gardens and fruit-bearing trees. And certainly not in the compost pile. Moderation is a wise course of action if you're not willing or ready to become totally immersed in the organic way.
Even with relatively safe pesticides, think about what and how much you're spraying, dusting or spreading. Toxins linger, some longer than others. Roots absorb the good and bad from soil. Give thought to how that could affect home-grown edibles and the environment in general.
Prior to last year, pressure-treated wood for residential use was infused with chromated copper arsenate. OK, arsenic. The substances were infused into the wood to kill insects and protect against rotting. Treated wood can last 30 to 40 years.
Readers frequently asked about its safety for use in building raised vegetable beds. Even though some studies insisted there wasn't a problem with the poison leaching into soil and up into our carrots and potatoes, other studies disagreed.
Banning arsenic from pressure-treated wood for residential use in
2004, the Environmental Protection Agency has opted for "lower-toxicity pesticides." Good old redwood is still my choice for raised vegetable beds. Why take a chance?Use pressure-treated wood for deck supports and privacy fence posts. The stuff works.
Jim, a gardener from Fair Oaks, asks if composted walnut leaves will inhibit plant growth. Black walnut trees have a chemical growth inhibitor (juglone) that is strongest in its roots, less so in the leaves. Juglone can kill tomatoes, apples, azaleas, peppers and other susceptible plants.
According to the Ohio State University extension: "Walnut leaves can be composted because the toxin breaks down when exposed to air, water and bacteria. The toxic effect can be degraded in two to four weeks."
Shredded leaves will decompose faster and the toxic effects are diluted when leaves from other trees are mixed with walnut. But, to play it safe, compost leaves other than black walnut. Don't ever use whole, uncomposted black walnut leaves as mulch.
Jim also asks if oak leaves can be composted? Yes. Although studies have shown that oak leaves really don't make soil acidic, others believe otherwise and insist they make great mulch around acid-lovers such as azaleas.
What not to compost
- Meat or meat products, such as gravy, fats and bones
- Dairy products, such as cheese, whole eggs, sour cream and milk
- Used pet litter or pet feces
- Ashes from a coal stove or charcoal ashes
- Diseased garden plants
- Invasive weeds (seeds can survive if the pile isn't hot enough)
- Poison ivy
- Grass clippings treated with pesticides or herbicides
- Sawdust from pressure-treated lumber
- Chips or sawdust from black walnut, eucalyptus, red cedar and other allelopathic trees with aromatic oils. Allelopathic plants produce chemicals as a defense mechanism to kill off competing plants nearby.
Source: "Composting" by Liz Ball (Workman Publishing, $10.95, 106 pages)