Cultivating Service

5 rules for fighting weeds

Dan McGrath, a vegetable crops specialist with the Oregon State University Extension Service, offered our Master Gardener class the following pointers for dealing with weeds:

Dan McGrath, vegetable crops specialist for the OSU Extension Service, shows examples of weeds to a Master Gardener class on Jan. 17, 2013. (Photo by Denise Ruttan)

No. 1: Have a Plan B … and C … and D …

Whatever strategy you use to combat weeds, he says, will work for a while until something finds a way to beat your plan. This “weed shift” happens when a species becomes highly dominant. Sometimes it’s because of the environment, but often it’s because gardeners use the same strategy over and over again. Never assume you have everything under control.

No. 2: Know your enemy.

In what season is the weed growing? Is its root system fibrous or creeping? Is it an annual or creeping perennial weed? If it’s an annual, is it a summer or winter one? An annual grows for one year, spreads lots of seeds and grows fibrous roots. Perennials have creeping roots and they’re tough to kill and impossible to mulch.

No. 3: Make weeds unhappy.

Weeds grow in conditions that make them happy. When you till or break up soil, that disturbed soil then offers all the goodies a weed needs: nutrients, moisture, light and space. Any of those factors will attract certain types of weeds.

No. 4: Know your weapons.

The trowel and hoe are a gardener’s go-to tools. But if you only weed by hand, weeds will become resistant to this method, McGrath said. He cited an example from his work with rice farmers in Indonesia. Standing in a rice paddy, he looked down at his feet and noticed a hand mark in the dirt. Each plant was weeded by hand. But there was another plant growing there, too. It looked exactly like a rice seedling. It was a type of weed known as a “mimic,” resistant to hand weeding.

To prevent resistant weeds in our own gardens, McGrath advises using cover crops. Plant a crop such as fava beans that you put in during the fall and till in the spring when it flowers. He also recommends using companion planting, or plants that enhance each other’s growth and can crowd out weeds. He also says to time your planting and to plant different crops in succession because different weeds grow at different times. Finally, you can use herbicides, he says, but don’t rely just on them because weeds can become resistant to them.

No. 5: Know yourself.

“The toughest thing to do when analyzing a weed problem is trying to figure out what the person is doing to contribute to the problem,” McGrath said. We don’t like to admit that we may be causing the problem. McGrath showed a picture of a farmer spraying a pesticide along a road where star thistle had spread along the ditches because it had become immune to the chemical. So the farmer changed his strategy and planted a cover crop, creeping red fescue, along the ditches. The crop is easy to maintain and it prevents the weed from growing without pesticides.

Microorganisms make life out of somebody else’s trash

Master Gardener Teresa Matteson, now on the education and outreach team for the Benton Soil and Water Conservation District, took our class outside into the chilly January air to show us some compost bins.

Teresa Matteson with the Benton Soil and Water Conservation District describes equipment used in composting to a Master Gardener class in Tangent on Jan. 17, 2013. (Photo by Denise Ruttan)

She explained that anything once living could decompose: grass clippings, leaves, flowers, weeds, twigs, and hedge clippings. The rate of decomposition depends on air, water, size, time and the carbon-to-nitrogen ratio. You can adjust those factors to speed up or slow down the process.

Matteson, a former coordinator of the Master Composter Program through Recycling PACT (People Acting Change Tomorrow) in southern Oregon, recommends starting compost piles anytime.  

Begin by forming a 12-foot piece, ½-inch hardware cloth, a type of welded wire mesh, into a column.

Then dump in six inches of your coarsest compostable material. Add three inches of green matter like grass clippings, then some water and a little soil. Mix those layers together and repeat until the column is filled. Let it sit for three weeks to heat up then turn to introduce more oxygen into the mix.

Matteson showed us a bucket filled with leaves, grass and other organic matter. Another bucket was filled with that material, except now it was mushy and uneven.  Little organisms, tinier than the eye can see, were hard at work gobbling up the yard clippings, manure and leaves. Somebody else’s trash was their treasure.

Then we Master Gardener trainees, huddled in a circle, gasped collectively in astonishment at a bucket filled with finished compost. Rich, brown, aromatic, fantastic compost. It was what all that yard debris had become. Matteson sifted her fingers through it. The fresh, warm odor of a forest floor wafted toward my nostrils.