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Keeping the Wild Weeds Out of Wildflowers |
By Carl Wilson, Extension Agent, Colorado State University Cooperative Extension in Denver County
Wildflowers are beautiful but weed invasion is not.
The "wildflower look" has appeal for many reasons. One is relief from the symmetry of rows of trees and ordered flower beds so prevalent in the rest of the landscape.
Sadly, this wild beauty is easily spoiled by invasion of weeds, such as mallow and bindweed. This can happen within one or two years after planting. Research into weed control by the Department of Horticulture at Colorado State University has found several ways to thwart the weeds.
The first is to eliminate weed seed from the planting area before seeding wildflowers. Following soil preparation, complete two cycles of watering, allowing weed seedlings to grow, and spraying with glyphosate (Roundup, Kleenup). Allow about ten days for the chemical to kill the weeds before repeating the process.
Completing two cycles of this spraying and waiting will take about a month. This procedure eliminates weed seed from the top layers of soil. Deeply buried weed seed isn't likely to germinate.
Now you're ready to plant. Do not cultivate the soil again before scattering your wildflower seeds. Stirring the soil will bring up buried weed seed and defeat your efforts.
Note that an area infested with tenacious perennial weeds such as thistle and bindweed may require a growing season's worth of repeat sprayings to kill persistent roots. This program likely is necessary whether wildflowers or any other type of planting is planned.
Once established, cut wildflowers back to half their length at midseason. This cutting not only prevents weed seed production, it also rejuvenates the wildflowers leading to better late summer bloom. Use a string trimmer or hand cut small plantings with a hedge sheers.
Much to the disappointment of some, selective hand weeding is still recommended. Pull weeds when soil is thoroughly moist using care to disturb as little soil as possible. The more subsurface soil you uncover, the more weed seeds will germinate.
The last tip for preserving the "wildflower look" is to appreciate the cycle of nature in terms of wildflower succession through the seasons. As a survival strategy, many wildflower seeds are programmed to delay germination for several years.
Some wildflowers will be plentiful in certain years and may not reappear in large numbers for three years or more because of moisture, temperatures and other natural conditions. Others, such as coneflower (Ratibida) and snow in summer (Cerastium), will likely become dominant. Yearly seeding of additional wildflowers into the plot will help to crowd out weeds and maintain the look you want.
Wildflowers excel at lending a feeling of informality and providing a showy display of color in the landscape. Following these tips will help maintain wildflower beauty free of ugly weeds.
An information sheet titled "Wildflowers in Colorado" (CSU Fact Sheet 7.233) provides suggestions on wildflower species adapted to the state. You can request it from any county office of Colorado State University Cooperative Extension.
Photo: Judy Sedbrook
