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How Do I Keep Crabgrass Out of My Lawn?


The thing about crabgrass is that it is, well, it’s a grass. And, your lawn is also grass. So, if you want to kill one kind of grass (crabgrass) but not another (your good lawn grass), what do you do?

You may know that there are herbicides that can kill dandelion, clover and many other lawn weeds without harming your good grass. The material used in these treatments is called a ‘selective herbicide’.  This means that the herbicide can ‘selectively’ kill weeds – it will kill the weeds, but not the grass, in your lawn. This works because the dandelions and other weeds are not grasses. They are in a group of plants called ‘broadleaf weeds’. Unfortunately, a selective herbicide will not work on crabgrass.

Crabgrass is an Annual Weed Grass meaning that it grows from seed each year and dies at the end of the year. Crabgrass Preventer is a type of herbicide that can prevent the crabgrass seeds from growing. The concept is, if the crabgrass seeds do not grow, you will not have crabgrass plants in your lawn. This is different than most weed control products that typically treat actively growing weeds.


Pre-Emergent vs Post-Emergent Weed Control

It is helpful to understand the difference between Pre-Emergent and Post Emergent weed killer. A Pre-Emergent herbicide does the job of killing the weed ‘before the plant emerges’ from the seed. A Post-Emergent product is used on plants that are actively growing (‘after the plant emerges’).  Also, the terms ‘pre-emergent’ and ‘crabgrass preventer’ mean the same thing.

Since Crabgrass Preventer is a pre-emergent, it will not work on crabgrass that has grown beyond being a seed. If you see leaves (grass blades) on crabgrass, it is too late in the season to use Crabgrass Preventer.  There are post-emergent crabgrass herbicides that, if used properly, can be used to kill actively growing crabgrass plants without harming the lawn grasses. Green Giant includes post-emergent treatments of crabgrass in many of our lawn care programs.

Typically pre-emergent products are advertised to work for up to four months.  While this is true, there are conditions that can cause the crabgrass preventer to fail prior to four months. It is important to understand, that crabgrass preventer cannot do the job of preventing crabgrass on its own – in a way, it’s a team effort.  One part of the team is the crabgrass preventer and the other parts are discussed below.


Why Didn’t My Crabgrass Preventer Work?

The Team Effort requires:  Crabgrass Preventer and the following:

A healthy, thick lawn – To keep crabgrass out, there needs to be competition – that is, your good lawn grass. Crabgrass preventer works very well with the help of a dense lawn. It is hard to prevent crabgrass in bare and thin areas of a lawn.

Proper Mowing Height – A lawn that is mowed too short will make it easier for crabgrass to grow – even with a crabgrass preventer treatment. Grass mowed at 3” – 4” will shade the crabgrass seeds and compete for water and nutrients when the crabgrass is attempting to sprout. This makes the crabgrass plant weaker and the crabgrass preventer more effective.

The Right Amount of Rain – Ok, we can’t do much about this but, it’s good to understand the affects of excessive rain. Over time, crabgrass preventer breaks down. And, the more rain there is, the faster this will happen. The ability of the material to stop weed seeds a month after the application is much greater than the material’s ability three or four months down the road.  Also, in a wet summer, crabgrass seeds are continually germinating.  The combination of these two situations will often cause crabgrass breakthrough. There is still a level of effectiveness three – four months after the application –but it is reduced. And, when there are fewer seeds germinating (in a dry summer), the small amount that will breakthrough is not usually very noticeable.


Crabgrass is not the easiest weed to deal with but, with the ‘team effort’, the crabgrass preventer can do a great job.


Lawn Care

Green Giant Home & Commercial’s Lawn Care services control weeds, build the thickness and density of your lawn and protect it from being damaged by insects and disease, providing you with a great-looking, healthy lawn. We offer fertilization, weed control, liming, insect control, and aeration and overseeding. Visit our Lawn Care page for more information.

Tree Care

Green Giant performs: Proper Diagnosis and Treatment of Tree & Shrub Problems, Insect & Disease Control (including Spotted Lanternfly), and Nutrient Management via Deep Root Fertilization to keep your plants healthy and thriving. Visit our Tree Care page for more information.

Vegetation Management

Green Giant’s Non-Lawn Weed Control services eliminate unwanted vegetation in a wide variety of locations for both residential and large commercial/municipal properties. Areas include fence lines, around obstacles to reduce weed eating, stone/gravel driveways & parking lots, swales, roadside/curbside vegetation management and more.  Find more information, visit our Vegetation Management page.

Pest Control

Our full service pest control division provides both Year-Round Service Programs that cover the vast majority of pests that you will encounter and also One-Time Corrective Services for pests such as bees, ants, termites or mice. For more information, visit our Pest Control page.