To keep weeds out of the lawn, a good defense is the best offense. To encourage a stronger healthier lawn, let the grass grow until it is four inches tall before mowing with a cutting height of two inches or more. Letting the lawn grow longer makes the roots stronger and decreases the room weeds have to get established. Reseeding bare patches is a good proactive approach to prevent weeds from getting a foothold.
Pre-emergence herbicides, like weed-and-feed, are only effective at preventing crabgrass and annual weeds from germinating if applied precisely before the growing season. These weed-and-feed products do very little to stop perennial weeds that are already established. Apply broad spectrum and selective week killers early in the season. Later, mature weeds require multiple applications of weed killer since they can grow back from their extensive roots. Glyphosate, (RoundUp) is a broad-spectrum herbicide that kills all weeds, including grass. Avoid over-spray on plants and shrubs. Rain and irrigation systems will wash weed killer off the leaves. To make the most of the product, apply weed killer when rain is not in the forecast for at least 24 hours. Depending on the active ingredient, weeds will be dead within hours, or can take up to two weeks to fully absorb the chemicals.
When choosing a weed killer, carefully read the directions, making sure the herbicide is effective on the problem weeds in your yard. Selective herbicides are generally broken down into two categories, broadleaf, or grassy. Broadleaf herbicides have multiple active ingredients and will also kill St. Augustine grass.
Pesky weeds like sedge, also known as nut grass, grow from tubers (“nuts”) embedded over a foot below the surface. Nut grass can easily be identified by its triangular flower stems. When nut grass is pulled from the ground, the fleshy stems separate from the tuber, allowing the tuber to re-grow. These aggressive plants require specialized herbicides like Image, or SedgeHammer, previously called Manage. Follow the package directions, allowing the plant to retain intact for at least two weeks, so the herbicide can be absorbed all the way down to the tuber.
Weeds are some of the most prolific spreaders, releasing billowing seeds to all corners of the yard if given the chance. Mechanical weed removers stab fleshy roots, like dandelion, and pull them from the ground with the aid of a foot pedal. Dandelions are one of the weeds that can back after weed killer applications. For these strong plants the best course of action is to sever the root, or wait until autumn to use weed killer when the plants will have less opportunity to regenerate.
The best cure for weeds is prevention. Fertilize your lawn, deal with any pest problems affecting growing, and remove weeds that are already creeping in, before they prepare to launch a hostile takeover that will be more difficult to manage.