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On The Weed Warpath

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by Vera Strader, Master Gardener- “To tell if it´s a weed, pull it up; if it´s gone for good, it was a flower!

If it comes back, it´s a weed”—or so goes an old axiom. Often true, although the weed that comes back is more likely the seedling of that earlier weed. Weeds are enthusiastic and wily spreaders. Some stealth weeds seem to go to seed before they´re barely even up.

You can still head off much of next year´s weed progeny by sabotaging weeds´ powerful urge to reproduce–either by averting seed production or foiling the germination process.

PREVENT SEEDING. To foil seeding, eliminate the entire plant or whack off the flower heads before they can mature. Timely weed pulling works, but it can be an overwhelming chore.

Mowing will clobber certain weeds though timing is critical. Mow too late and the weed has already performed its dirty seed-spewing deed. Mow too early and some weeds retaliate with new stems and even more flowers and resultant seed heads closer to the ground. Yellow star thistle is an example of this devious weed tactic. Mow star thistle as it “shows yellow” when just coming into flower.

THWART GERMINATION. Many weed seeds can lie dormant for years waiting for the chance to come up for air and light. These opportunists love it when we till the soil. Instead, thwart germination with soil solarization or with landscape fabric and/or mulch. When solarizing, cover smoothed moist soil with clear plastic; allow six weeks for it to work during the hottest months.

There are various kinds of landscape fabric and, unlike the old black plastic so often used, landscape fabric allows desirable air and water through to the soil. Top with a layer of mulch.

Mulch—lots of mulch—is the time-honored way to downsize weed germination and for good reason. Not only does mulch smother seeds and reduce germination from the get- go, it reduces watering by keeping the soil cool and moist. Many mulches decompose, improving soil quality. When weeds do manage to make it through mulch, you can more easily yank them out.

A two-inch layer of fine mulch and up to four inches for coarser ones does wonders. Keep mulch away from the crown of your plants to prevent fungus diseases.

Organic mulches made from once-living plant or animal materials do double duty. This includes chopped leaves, grass clippings, and compost from your back yard compost pile, worm bin, or from the garden center. Aged barnyard animal manure, usually a combination of animal droppings and plant materials, adds extra nutrients. Over time these organic mulches break down, loosening and enriching the soil. However, they do need occasional replenishing.

Bark, too, is an organic mulch and, although the coarser types break down slowly—thereby lasting longer, they are less valuable for soil enrichment and less adept at weed suppression. Inorganic mulches like gravel and stones don´t readily decompose and are effective on pathways and on dry and rock gardens.

IDENTIFY NOXIOUS WEEDS. Some weeds can be truly invasive requiring strong-arm tactics. These weeds out-compete our native plants, choke streams and displace meadows. Some even employ chemical warfare by releasing substances that inhibit growth of other plants—a process called allelopathy.

Noxious weeds may be “exotic” invaders like Italian and Russian thistle (tumbleweed) inadvertently brought from other lands; others are ornamentals run amok. Vinca and ivy, for example, literally go underground with roots and runners; some—like Bermuda grass—resort to a terrorist combination of roots, runners and seeds.

PLAN COMBAT STRATEGIES. A plant is a weed only if it grows where unwanted. Weeds act as Mother Nature´s ground cover helping control erosion, provide food for domestic animals and invaluable habitat for wild birds, animals and insects. Choose your weed battles carefully and deploy the big guns only when weeds truly justify guerilla tactics.

For help devising combat strategies including weed identification, solarization techniques and the selection and timing of appropriate preemergent and postemergent herbicides, call Master Gardeners at 209-533-5696 or consult UC Pest Notes at See you in the garden.

Vera Strader is a Sonora Master Gardener who uses loads of organic mulch each year to enhance her wildlife friendly yard.