When to apply crabgrass preventer before or after rain

Crabgrass is a tough grassy weed that can be successfully controlled with a good pre-emergent herbicide applied at the correct time. So, when should you spray your lawn with a crabgrass preventer?

It’s important to remember that a crabgrass pre-emergent herbicide won’t prevent the weed from germinating. It simply stops crabgrass from growing roots, allowing your grass to outgrow and destroy the weeds. If you apply the crabgrass preventer too soon, it may break down or weaken, rendering it ineffective in preventing crabgrass and other tenacious weeds from germinating. This is why pre-emergent timing is so crucial in this case.

In this article, we’ll tell you about the factors that you should pay attention to when deciding when to apply a crabgrass preventer.

Crabgrass weed growing on a grass lawn
Crabgrass on a lawn

Best time to apply crabgrass preventer

Early Spring

Crabgrass begins to germinate as the weather warms up in the spring. The spring calendar is a useful signal to keep in mind when deciding when to plant crabgrass pre-emergent. A seasonal calendar will help decide the optimal time to apply a crabgrass preventer because spring does not begin on the same day every year.

For example, spring begins on Saturday, March 20 in 2021. This is an excellent time to work on your lawn and use herbicides to avoid early weeds, which include both broadleaf grassy lawn weeds and grassy lawn weeds.

Crabgrass seeds germinate from seeds that were dropped in fall or summer. The seedlings stay within the soil all through the winter months and begin to germinate when the weather starts to become warm, usually in the spring.

To stop the growth of crabgrass on your lawn, apply a pre-emergent early in the spring since this is when the weed begins to sprout.

Between the end of March and the beginning of April are the perfect time to apply a herbicide that is pre-emergent like Snapshot to ensure your protection throughout the season.

Warm Soil Temperature

The sun begins to shine in the spring. Because the sun heats up the soil and activates enzymes that promote seed germination, this is when a large number of plants germinate.

Crabgrass seeds grow when the soil temperature reaches around 55 °F to 60 °F, which normally happens between late spring and mid-summer.

Other elements such as wind, shade on your lawn, and the climate where you live can all alter the temperature of your soil. As soon as March begins, start taking the temperature of your soil on a daily basis.

Before or after rain?

Apply crabgrass preventer right before it rains so that rainwater can wash the herbicide down into the soil where it will contact germinating crabgrass seeds. It’s best to start applying the pre-emergent in early spring, when the weather prediction forecasts rain in a few hours.

If it doesn’t rain, water the lawn right away or within 2 to 3 days of applying the pre-emergent to ensure that it is soaked down into the soil and stops crabgrass from growing. Or irrigate the lawn according to the product label.

Because heavy rain might wash away the herbicide, you may need to apply it one or two more times to guarantee complete coverage of your lawn’s soil in crabgrass pre-emergent.

Rain could be a factor in choosing the timing to use crabgrass preventer
Rain could be helpful for crabgrass prevention

Keep a close eye on the weather forecast in your area. Start applying a crabgrass preventer to your lawn as soon as the forecast predicts rain in the next few hours.

Dogwoods and forsythia blossom

Forsythia plants begin to blossom from mid-March to mid-April. It is the time when temperatures begin rising to signal the beginning of spring and the end of winter. If you can see the waterfall of vibrant yellow flowers forsythia this is an indication that it is time to apply crabgrass preventer herbicide in order to prevent the germination of weeds.

If there aren’t any forsythia trees in your area you can use dogwoods to determine your timing.

Forsythia blossoms in early spring
Forsythia in bloom

Dogwoods have beautiful white flowers that are usually blooming from mid-March to mid-May. When you spot these blooming flowers, it’s an ideal time to use your pre-emergent herbicide in order to prevent the growth of crabgrass on your lawn.

Can you apply crabgrass preventer in fall?

Temperatures start to drop in fall so crabgrass seeds won’t be germinating during this time. There’s no need to apply a crabgrass preventer in fall. The low temperatures and frost will kill crabgrass and leave bare spots that’ll need overseeding to fill them up.

Is it too late to apply crabgrass preventer?

When crabgrass has germinated on your lawn, it is too late to apply a preventer. A pre-emergent herbicide is designed to prevent crabgrass seeds from sprouting and forming roots. If you already have young shoots of this weed on your lawn, you’ll need to use a post-emergent crabgrass herbicide to control it.

Also, by the time soil temperatures begin to decrease at the end of spring, it is too late to apply crabgrass pre-emergent because the grassy weed’s second wave of germination will occur in the spring when temperatures begin to rise again.

When should you apply crabgrass preventer in your specific area?

Because weather and temperature vary so much from state to state, it’s crucial to remember that what works in Michigan might not work in Texas. Use GreenCast’s interactive map to see when the soil temperature in your area will be suitable for applying crabgrass preventer. To find the soil temperature this year, simply enter your location and the date. The average of the previous five years, as well as the average of the previous ten years.

Keep in mind that the temperature of your lawn’s soil might be affected by shadow or wind. Self-testing the temperature is the most reliable method. Many pre-emergent crabgrass killers also state that they should not be used in hot weather. In the heat, harsh chemicals accelerate, potentially injuring your lawn.

How often should a crabgrass pre-emergent be applied?

Because most weed pre-emergent herbicides last up to 6 months, using this tool twice a year is strongly advised.

Allow at least 2 to 6 months between applications, and avoid applying to a freshly sown lawn. Some pre-emergents can cause grass seed species to germinate slowly or poorly.

Is it possible to apply crabgrass preventer on wet grass?

Because the liquid concentrate will wash down into the soil and prevent weeds from growing, you can use liquid crabgrass preventers on wet grass.

However, applying granular crabgrass preventers on damp turf is not a smart idea because the herbicide will just attach to the moist leaves and have no effect on weed management.

If you apply the herbicide while the grass blades are still wet, make sure to thoroughly water the lawn to remove the pre-emergent from the leaf blades and into the soil.

Should you water your lawn after applying the crabgrass preventer?

It is true that watering the lawn prior to applying the pre-emergent is an excellent method to ensure that the herbicide soaks into the soil, allowing it to come into contact with crabgrass seed. Make sure to water your lawn immediately after applying pre-emergent herbicides that are solid.

The only instance when you may not need to water your lawn is when you use a liquid crabgrass preventer because the concentrate is able to be absorbed into the soil to fight weeds there.

How to apply crabgrass preventer

After you’ve determined the right time to apply the pre-emergent to kill crabgrass it is important to make sure that you know the proper way to do it. The majority of preventative treatments will be liquid and have to be applied using the aid of a hand-held sprayer or backpack. Some are water-soluble and must be applied in the same way following mixing.

Always be sure to study and adhere to the instructions on the label when mixing and diluting. You must be careful not to increase the dose, as it may cause harm to turf grass. When you apply make sure that the grass isn’t wet. If there was heavy morning dew, you can wait an additional few hours during the day to ensure that the grass is dry. The solution does not simply adheres to grass blades but penetrates in the earth. Remember, the water after application will assist in letting the solution soak deep into the soil.

Using liquid crabgrass preventer
Worker spraying liquid crab

Spray in even strokes across the grass. Make sure you get the edges of your lawn. Crabgrass thrives where the soil is the hottest (near concrete or pavement). Make sure you follow the guidelines the label recommends and don’t let traffic pass on your lawn for the entire day.

Seeding following the laying down of crabgrass preventer

How long should you wait after putting in a crabgrass preventer, to plant your seed? It’s recommended that you wait from two weeks to six months after the application of the crabgrass preventer before seeding your lawn. It will, however, depend on the herbicide employed.

There are two kinds of crabgrass preventers:

  • Short residual pre-emergent
  • Long-residual pre-emergent

Short residual pre-emergent herbicide will still be potent 60 days after application. It is recommended to fertilize your lawn following this time.

Long-residual crabgrass preventers can stop the growth of crabgrass throughout the year. Only apply them to existing lawns in order to reduce the spread of crabgrass.

Dimension 2EW Herbicide is a water-based herbicide that provides long-term control of crabgrass. Team, as well as Scotts Halts, are examples of shorter-term pre-emergents.

Seeding too soon after the application of crabgrass preventers may result in slow and uneven growth of grass seeds. Certain brands may hinder seed growth at a high rate.

For instance, Scotts Halts crabgrass preventer will prevent bentgrass from germinating. Beware of using the product as an early-emergence agent if you plan to seed your lawn using creeping bentgrass or dichondra.


The ideal time to apply the crabgrass preventer is at the beginning of spring when the soil temperatures begin rising to reach 55 degrees Fahrenheit. Apply the pre-emergent before it rains to ensure that the herbicide washes through the soil. Forsythia and dogwood blooms are a good indication to begin applying the crabgrass preventer.

Crabgrass near a concrete
Crabgrass near a concrete

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