Using a Pre-Emergent Herbicide to Control Crabgrass

Crabgrass can be the bane of the home landscape gardener but you can attack the problem by using a pre-emergent herbicide. Weed control may require a combination of methods, though, which can include not only herbicides but also weed germination prevention.

How Pre-Emergent Herbicides Work

A pre-emergent herbicide is a weed killer that is designed to prevent seeds from germinating and growing early in the growing season. This is particularly relevant with crabgrass eradication efforts because crabgrass is an annual plant that sprouts from seeds. The seeds have been left behind by the previous year’s crabgrass growth and lie in wait all winter until the soil begins to warm so that it can germinate and grow.

The herbicide creates a barrier seal around the seed, essentially suffocating it by preventing it from sprouting to form a new plant. Pre-emergent herbicides are generally very effective in helping reduce and even eliminate crabgrass growth, provided they are applied correctly and the seal is not broken by aeration.

Applying the Herbicide

There are two methods of applying a pre-emergent herbicide. You can spray liquid weed killer on the crabgrass or spread herbicide granules on it.

Liquid pre-emergent herbicide can be purchased at almost any home improvement center or garden nursery. Spray the weed killer in places where you know crabgrass has grown in the past, since this is where seeds will probably be located in the new growing season.

The other method of applying the weed killer is by spreading it over the lawn. Granules are usually combined with fertilizer, so many homeowners prefer this method for lawns, particularly if they have a large problem with crabgrass. Using a spreader, either handheld or wheeled, will distribute the granules evenly across the lawn. Activate the granules with water from the sprinkler system or hose. If you use the herbicide shortly before a spring rain storm, you should obtain good results in killing the crabgrass.

Regardless of whether the weed killer is applied by spraying it or by spreading it in granular form, you should apply when the weather is still cool.  It should not be applied if the weather is warmer than 60 degrees.

Other Prevention Methods

You can discourage the growth of crabgrass by spreading landscape fabric or burlap over an area where the growth of the weed is likely. This is a particularly effective method if you have large areas of bare ground, since crabgrass especially grows where access to sunshine is available.

During the heat of summer, you can spread clear plastic sheeting over an area of bare ground or to an area where you have a heavy infestation of crabgrass. This method is only recommended if there are no other plants in the area, since summer sun will heat the plastic and can kill plants.

The best preventative for getting rid of crabgrass is good lawn care. Allow the lawn to grow to at least one-third of expected blade growth instead of cutting it too short. Crabgrass thrives in sunshine and longer grass shades crabgrass seeds from thriving and sprouting.