When Does Crabgrass Die? Best Time to Apply Killer

Crabgrass is a warm season annual plant that germinates, thrives and dies all in the same season. However, it remains to be one of the difficult weed to control in many lawns. This is mainly due to improper timing when applying a crabgrass killer. So, when does crabgrass die?

Crabgrass dies in fall as soon as it is hit by frost. As it dies, it leaves behind thousands of seeds that will germinate the in spring through late summer when the soil temperature is above 55°F for at least 4 or 5 consecutive days.

When Does Crabgrass Dies?

The best way of controlling crabgrass in a lawn has to begin by understanding its life cycle. Crabgrass reproduces by seeds, which germinate from spring through late summer when the soil temperature hits above 55°F for at least 4 or 5 consecutive days.

Crabgrass will continues to grow until midsummer when days become shorter. By this time, the vegetative growth of this weed slows and plants enter their reproductive stage. It will then start forming and dropping seeds until it gets killed by the frost.  Crabgrass seeds will remain dormant in the low temperatures until spring when the weather warms up.

Crabgrass is very adaptive to high temperatures and dry soil conditions which are usually unfavorable to most turf grasses. This makes the weed very competitive when the rest of your lawn is stressed. For this reason, crabgrass will rapidly spread, and take up your lawn.

Why is Crabgrass Bad

Crabgrass is very much noticeable in a lawn. It is easy to spot this coarse textured yellowish-green grass in your fine textured grass. Once established, this weed is difficult to control and unfortunately it will keep on chocking out your desired grass. Beyond this stage it also become difficult to get rid of crabgrass in your lawn.

Mowing a lawn short is one of the effective ways of controlling weeds but that does not usually apply to crabgrass. Ironically, crabgrass can set seed heads when cut as low as 1/2 inch tall— that’s far lower than recommended healthy mowing heights for most common turf lawns.

Crabgrass cannot be controlled in one growing season due to high number of viable seeds that will keep germinating in future years. This means you will need to be tactical and more patient to completely eliminate crabgrass in your lawn.

The physical structure of crabgrass is also known for creating a perfect hiding and breeding spaces for pests. This doubles the problem of dealing with both weeds and other pests in your lawn. Now you know why crabgrass is really bad.

Crabgrass Management Techniques

Satisfactory control of crabgrass needs deployment of both cultural and chemical approaches. The process also requires several seasons of consistency in the management approach.

Proper lawn maintenance has been proven as a defense against crabgrass infestation. Maintain a healthy lawn in summer by fertilizing, deeply watering and cutting grass higher. This will naturally discourage the growth of crabgrass in your lawn.

Properly applying pre-emergent herbicide in spring and post-emergent herbicide in summer can help in keeping crabgrass out of your lawn forever. Pre-emergent herbicides kill weed seedlings early in the growing season as they germinate, which prevents the weed plant from sprouting. Post-emergent herbicides on the other hand kill the already germinated and established weeds.

When to Apply Crabgrass Killer

Proper timing in application is very critical in effectiveness of a crabgrass killer. Let’s look at when to apply a post-emergent and pre-emergent herbicides.

Post-Emergent Herbicide      

A post-emergent crabgrass killer can help control the already germinated or established crabgrass seedlings. Early summer is the best time to apply a post-emergent crabgrass herbicide right when the weed has germinated. Directly apply your post-emergent herbicides to crabgrass plants on a calm, sunny day.

The application should be done in the morning when the temperatures are calm. If you are dealing with established crabgrass plants, a reapplication of the herbicide need to be done 5 to 10 days apart. There is no need to apply a post-emergent in fall as the plant has already dropped the seeds and waiting to die in frost.

Pre-Emergent Herbicide

Pre-emergent herbicide will kill crabgrass seedlings early in their growing stage, usually before the weed sprout out of the soil. These herbicides are also known as weed preventers. Application is done directly on the soils. Most pre-emergent herbicides are usually not effective in temperatures above 90 degrees Fahrenheit.

The best time to apply crabgrass pre-emergent herbicide is from March to May and preferably when the soil temperatures have reached above 55°F for 4 or more consecutive days. Application can be done as early as January in warmer climates like California’s.

Sometimes it is difficult to determine the soil temperature without using a soil thermometer. You can watch other signs like weeds sprouting by your paved areas like driveways, sidewalks, or patios. Also apply a pre-emergent when bushes like Forsythia start blooming in your area.

NOTE: If you are creating a new lawn from seeds, or reseeding bare spots, crabgrass killer herbicides may harm your lawn seeds. Be sure to read label instruction before using your herbicide. There is always the waiting time before you do the planting.

Final Thought

Controlling of crabgrass in your lawn or garden can only be easy if you understand the weed’s life cycle. You should know when it germinates, set seeds and also when it naturally dies. Crabgrass can be controlled by consistent healthy lawn maintenance practices especially during summer or by timely applying a crabgrass killer.


  1. University of Massachusetts Amhest: Biology and Management of Crabgrass
  2. University of Maryland Extension: Crabgrass Lifecycle, Habitat and Reproduction
  3. University of Vermont Extension: Crabgrass Control

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