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Should you apply crabgrass preventer before or after rain?

A pre-emergent herbicide offers a practical and effective way of getting rid of crabgrass. Also known as crabgrass preventer, it works by stopping the weed before it emerges from the soil.

The best time for applying a crabgrass preventer varies. That is because crabgrass can grow in bare spots if it has enough supply of water and sunlight.

Since it is an annual weed, it spreads by seeds, instead of roots. Therefore, when it comes to eliminating crabgrass, the temperature of the soil must be right before you can use a crabgrass preventer.

But should you apply a crabgrass preventer before or after the rain? The best time to use a crabgrass preventer on your lawn is early spring before the rains begin.

This is because the temperature of the soil is usually above 50°F, which is an excellent environment for crabgrass to germinate.

The most ideal time to use a crabgrass preventer is at least 24 hours before it rains.

When it rains, running water will wash the herbicide into the soil, enabling it to stop crabgrass from germinating. You should also make sure that you are using the best crabgrass preventer. The ideal type is Scotts WeedEx.

Does crabgrass preventer need to be watered in?

As noted above, applying a crabgrass preventer before it rains is the best way of controlling the plant. But the rain must fall within 24 hours of application. If that does not happen, consider watering in the herbicide.

The water will get into the soil and create a barrier layer on top. When the young crabgrass seedlings come into contact with the barrier, they will die. For best results, water your lawn within 2-3 days after applying the chemical.

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Watering will activate the compound and help to eliminate the crabgrass. Ensure your lawn receives a half-inch of water within three days.

NOTE: The time it takes for the barrier to remain on top of the soil will depend on the concentration of the herbicide, whether you used granular or liquid chemicals.

Can you apply a crabgrass preventer on wet grass?

You can apply a crabgrass preventer on wet grass. The best time to do so is when the plant is actively growing. However, the chemical will stick to the leaves and not go down into the soil. A solution for that is to water your grass immediately after you spray the herbicide.

That will force the herbicide to go deep into the soil and create a barrier, thus preventing the plant from sprouting. If you do not wash the compound into the roots, its rate of efficacy will reduce significantly. But sometimes that tends not to be the case.

In other words, read the directions on the label of the product before using it. Some manufacturers recommend that you apply the chemical on dry grass and then wash it in.

In addition, you cannot depend on the rain altogether. If the lawn does not receive a quarter or a half-inch of rainfall, it will not break down the salty compound. In the morning, the dew will create a salt solution that will burn the plant.

Can I apply a crabgrass preventer in the fall?

Fall is a recommended time to apply the chemical to your lawn. The seasonal life cycle of crabgrass begins in early spring.

Once the cold weather in the fall starts, the grass dies off. When you treat your lawn in the fall, it will prevent the crabgrass from growing in the winter.

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Also, the treatment at this point will get rid of both perennial and annual weeds (crabgrass is an annual weed). But the temperature of the soil should be below 70 degrees for this to work well.

You can either use a granular or liquid preventer to treat your lawn. After applying the chemical, avoid aerating or raking the soil. It will damage the soil barrier that the crabgrass preventer has created.

Can I apply crabgrass preventer in the summer?

The best time of controlling crabgrass or applying the chemical is in spring or early summer. If you have not achieved this and the weed has grown in the summer, you will need to wait until fall.

The plant will begin to die on its own during this period. By winter, you will not see the grass on your lawn. Then, apply the crabgrass preventer in early spring to prevent its growth in the summer.

Alternatively, you can opt for post-emergence control of the crabgrass. However, the method is only practical when the weed is younger.

As it matures, the use of post-emergence herbicides becomes challenging. You will have to apply it multiple times, spaced between two and three weeks apart to achieve full control and eliminate it.

How soon after seeding can I apply crabgrass preventer?

If you have finished seeding your lawn, wait until the grass sprouts before applying the crabgrass preventer. That means to wait until at least until the grass is about 1-2 inches tall.

When you spray the chemical at this time, it will minimize the risk of damaging the grass seed. The grass will have emerged from the seed at this point.

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The risk is that the process will begin later in the season if you delayed the seeding. While that may seem satisfactory, it means watering your lawn more times as you get into the summer. But if you want a long-lasting solution:

  • Apply fertilizer and crabgrass on your lawn first.
  • Water the lawn or wait for rainfall so that the soil can absorb the chemicals.
  • Give it at least a week of watering if there is no rain.
  • Aerate and seed your lawn.

In this method, crabgrass preventer will have few adverse effects on the grass seed.

Should I mow before applying crabgrass preventer?

It is best practice to mow your lawn before treating it with a crabgrass preventer. The mowing needs to happen once a week or when the grass is three inches tall. Your mower’s blades must be sharp to avoid split stems.

A disadvantage of split stems is once you apply the herbicide, it will damage your lawn as a result of the stress caused by the blunt blades. With sharp blades, they will give you a clean cut, which helps the lawn grow well.


The best time of applying crabgrass preventer is in early spring before the rain. If it does not rain, watering down the chemical will drive it down into the soil and create a barrier that prevents the weed seeds from germinating.

If the plant has grown in the summer, consider waiting until fall to apply the herbicide. Although you can use a post-emergent herbicide, it will require several treatments to work effectively.

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