We are approaching the end of August, and it is time to organize our fall garden tasks. We think about planting trees and shrubs in the fall and harvesting our garden’s bounty. Most importantly we make a list called ”I’ll never do that again” because that part of our landscaping was disappointing or too much work.
One of the tasks we often do not think about in the fall is weeding because we are just so tired of dealing with weeds and wish they would go away.
In the past, I have written how 3 inches to 4 inches of mulch makes such an effective germination barrier for annual weeds. Different strategies are needed to beat back perennial weeds.
Fall is an optimum time to kill perennial weeds rather than just pulling them out to keep them under control.
The reason that fall is the time to deal with these weeds is that the plants are still growing vigorously. They have large root systems, often with storage roots to sustain the plants through the winter.
It is nearly impossible to dig out these root systems. I have tried and succeeded with morning glory, but it was hours of work and took three years! Most of us have better things to do with our time. Herbicides and patience to the rescue!
An herbicide is drawn down into the storage roots and weakens the perennial weed and eventually kills it.
So, this is the perfect time to use an herbicide of your choice.
First, read the instructions on the package and make sure it is labeled to kill your target plant. Then, decide on the delivery of the herbicide to be sure that you do not damage desirable plants.
The WSU Master Gardeners can help you make decisions about herbicide, or you can visit the website called PICOL: Pesticide Information Center Online (cru66.cahe.wsu.edu/LabelTolerance.html). It is a label database that helps you target a weed and select an herbicide that kills it.
After you have applied the pesticide, check in a week to 10 days to see if another application is needed to knock back the growth. If the weeds have been persistent for several years, it may take more than one season to eliminate the plant. That means that herbicide is applied in the fall, the next spring, and the succeeding fall before you notice a major diminishment of the plant.
The most pernicious garden weeds are horsetail (Equisetum arvense), and field bind weed or wild morning glory (Convolvulus arvensis), quack grass and dandelions.
All of these weeds respond to herbicide applications. But the product must be very carefully applied to prevent damaging desirable plants.
Be conscious of heat over 80 degrees that can cause the product to volatilize — that is, turn into a gas — and affect nearby plants. Also, even a breath of breeze can move the product to nearby plants.
Perennial lawn weeds can be treated with care in the fall, especially bent grass and yellow nutsedge. Careful application of the product is essential so large swaths of your verdant carpet is not spoiled
Other noxious weeds on uncultivated and disturbed lands, such as Canada thistle, Dalmatian toadflax and Kochia can be cut back to eliminate their seed heads (which need to go in the trash), and treat the remaining stems and leaves with herbicide.
You can continue to treat perennial weeds until a frost kills the tops or until the ground temperature is 50, at which point most plants stop growing. Look forward to a more weed-free life next year.
A WSU Master Gardeners of Chelan County column appears weekly in The Wenatchee World. Bonnie Orr is one of four columnists featured.