KC Gardens

Sneaky weeds are taking root in your lawn

Weeds like dandelions and henbit put down roots in fall.
Weeds like dandelions and henbit put down roots in fall.

They’re out there, making their annual appearance. They may not be highly visible until spring, but by then it’s too late to get rid of them. Look closely. The weeds are just waiting for spring’s arrival to burst forth in our lawns. Fall is the best time to get them under control.

Broadleaf weeds, dandelions, henbit and chickweed germinate in the cool, moist conditions of fall. They overwinter as small plants no larger than a quarter. Spring weather promotes the weeds’ growth and flowering. Once plants reach the flowering stage, they are difficult to control. Control is most effective now, when the small seedlings are establishing.

There are several products available in granular and liquid formulations that are effective for control of these germinating weeds. Each has advantages and disadvantages.

Liquid herbicides usually are more effective than granular products. Lawns should not be mowed for several days before and after the application to allow maximum uptake and translocation of the herbicide. Timing is important: It is best if there is no rainfall or irrigation water applied for at least 24 hours after the application.

Granular herbicides often come mixed with fertilizer, which can be convenient. If using a combination product, adjust your fall fertilization schedules accordingly. The grass should be wet when applying a granular herbicide. This causes the granular herbicide to stick to the foliage for maximum absorption.

Apply these products in the early morning when dew is present or after a rain. Once again, there should be no additional moisture for at least 24 hours after the application.

Grass seed planted in the fall should not be treated with an herbicide until the new seedlings have been mowed two or three times. Treatment timing will vary depending on what herbicide is being applied. Follow the instructions on labels proper application times for newly seeded lawns , or you will kill the tender, new grass.

Another advantage of applying herbicide treatments in the fall is that less damage is likely to occur to plants you don’t want to kill. Warm spring temperatures, winds and succulent plant growth create problems for trees, shrubs and flowers damaged by herbicide drift. Cooler fall temperatures and plants going dormant greatly reduce this problem.

Don’t expect a quick kill; weeds treated in fall just seem to fade away under the cooler conditions. In the spring, the lawn should be relatively weed-free without undesirable bright yellow dandelions, purple henbit and lime green chickweed. With properly timed weed control, the lawn will be a carpet of dark green come spring.

Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Got a question for him or other university extension experts? Email them to garden.help@jocogov.org or visit KCGardens.KansasCity.com.