Solarize those pesky weeds

Weeds, weeds, weeds — the bane of the gardener's existence. How do we get rid of them permanently?

"You probably won't," is the opinion of Bob Reynolds, Oregon State University home horticulture agent, who recently taught a class on the subject. Weeds not only have several ways of spreading themselves, including persistent underground roots, bird droppings and the wind; sometimes we spread them ourselves, as the seeds hitch a ride on our shoes, clothing or vehicle tires.

Besides that, some weed seeds remain viable for 40 years. So, no, we won't get rid of them permanently. But we can at least battle them and win — for a while.

If you have weeds growing in a place you'd like to put to better use, consider solarizing them. This method is completely organic, involving no herbicides and their side effects. It's also very effective, inexpensive and requires minimum labor — depending on what's growing there now.

Any size weed patch will work, although for maximum effect it should be at least 3-by-3 feet. First, mow the weeds as low as possible. Then, till it just enough so you can rake out any big roots. Rake it smooth so no big lumps of anything are sticking up.

Next, water the area well. The soil should be well moistened, but without standing puddles. Now cover the area with 1- to 6-mil clear — not black — plastic. Seal the edges with soil or cinder blocks so no heat can escape.

Now sit back and wait as our Rogue Valley sun heats that soil to 115 to 125 degrees. Keep your soil thermometer handy if you want to check progress. This temperature will be sufficient to kill weed seeds, as well as many fungi, bacteria and nematodes that may be plaguing your plants.

Leave the plastic undisturbed at least four to six weeks — longer if the temperature has not risen enough. The ideal time for this procedure is between June 1 and Sept. 1. Later than September, the process will take longer and may not be as effective.

At the end of the solarization time, suppress the urge to rototill. Most seeds germinate in the top 3/4-inch of soil. If you till it, you will bring up weed seeds from deep in your soil, and you will be back to where you started.

Instead, get into the habit of mulching to continue to suppress the weeds. Chopped leaves or other organic mulch this fall will make a wonderful winter blanket for your newly renovated area. I do not recommend the use of landscape fabric, however, as weed seeds can fall through it, sprout, and be very difficult to pull. Instead, keep an eye on your new vegetable or flower bed, and pull or hoe any new weeds as they appear, never letting them go to seed. As Bob Reynolds said in his class, "One year's seeding equals seven years of weeding." Be persistent, and you will win.

Coming up: George Tiger, retired OSU Extension agent, will teach a class on Growing Cane Berries in the Rogue Valley. The class will be from 7 to 9 p.m. on Tuesday, Aug. 9, at the Southern Oregon Research and Extension Center, 569 Hanley Road in Central Point. The cost is $5; call 541-776-7371 for information.

Carol Oneal is a past president of the OSU Jackson County Master Gardeners Association. E-mail her at

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