Strategy, tactics needed in weed war

Special to the Tri-City HeraldAugust 31, 2012 

— In the Art of War, Sun Tzu says, "Strategy without tactics is the slowest route to victory. Tactics without strategy is the noise before defeat."

When it comes to winning in the war on weeds, you need a sound strategy and smart tactics.

A number of summer annual weeds have their greatest rate of growth during the middle of summer. That's because these weeds have a different photosynthetic pathway (C4) that provides for optimum photosynthesis and rate of growth when temperatures and light are high.

Optimum growth for most of our garden plants and winter annual weeds occurs when temperatures and light are lower because they have a different photosynthetic pathway (C3).

It's not surprising to find weeds that have made the most of recent scorching hot weather while we were inside sipping lemonade. Now is the time to fight those summer annual weeds.

Get rid of them before they have a chance to spread their seeds for next year's battle. If you retreat without roguing out the weeds now, you will have more weeds year after year.

I know because five years ago, I let weeds take over a wine barrel planter that went unused for the season. I've used that planter for the past four years, and the weeds continue to keep coming up from the weeds that were allowed to grow five years ago.

Mulching to prevent weed growth

Mulches help control weeds by excluding light and preventing seed germination and growth. I use a three- to four-inch layer of shredded bark to control weeds in my landscape beds. It effectively prevents most weeds from growing.

I don't use any landscape fabric, plastic or other material between the soil and mulch. The bark mulch also helps keep the soil cooler during hot weather, conserves soil moisture and adds organic matter to my sandy soil. Gusty winds don't lead to blowing bark for me because the soil grade of the beds is four inches below the grade of the surrounding lawn.

NoteWhen using bark or other mulches around trees and shrubs, keep the mulch about four inches away from the base of the plant. Mulch that touches the bark can lead to crown rot by keeping the bark moist and may also encourage damage from rodents during the winter.

As much as I like bark mulch, I don't advocate its use in areas vulnerable to wildfire. In those areas, inorganic gravel or stone mulches are advised, but keep in mind that they keep the soil and the area around the plant warmer.

In vegetable and annual flower beds, grass clippings (no more than a two inch layer), sections of newspaper (uncolored paper only) and finished compost can be used as organic mulches. Landscape fabric can also be used for some vegetable crops, such as tomatoes and peppers.

Next time, we'll continue our talk of the "art of war against weeds" and focus on chemical weed control.

* Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension.

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