When to Apply Crabgrass Preventer (Timing Before or After Rain?)

Most annual weeds such as crabgrass start to grow in the spring. During this season, the temperature of your lawn’s soil begins to warm up and provide a very good environment for germination.

Apply crabgrass preventer early enough in spring. The best timing for applying crabgrass pre-emergent is when soil temperature is between 50°F and 55°F (just before the onset of rains) This prevents germination of crabgrass weeds in your lawn. Scotts Halts, Bayer, and Ortho lawn weed killers recommend this timing.

First, you ought to have a very effective crabgrass killer. Second, timing is very important when it comes to such tenacious weeds. In order to control and prevent germination of crabgrass and other weeds, the best time to apply pre-emergent is before the onset of rain in the spring. The timing for this may differ depending on the climatic zone or region you fall in.

What’s the best time to apply crabgrass preventer?

Quick answer: Apply pre-emergent before and NOT after rain.

The main reason why it is a good practice to apply crabgrass preventer herbicides before it starts to rain is that the water from the rain will wash off the herbicide into the soil and the crabgrass seed. In the process, you kill the seeds before germination.

You should, however, be careful not to apply crabgrass preventer too early because it will break down and become less effective. This way, it will allow the weeds to germinate soon after it rains.

Your timing needs to be perfect for the best results. Here are tips to help you with that.

  • Take and track soil the temperature of your lawn. The best time to apply a crabgrass pre-emergent is just before the rain when the temperature is between 50 and 55°F.
  • You can observe dogwoods and use them as an indicator. In this case, start the crabgrass control measures just before the dogwoods begin to bloom (usually late April to Early May).

Most good crabgrass pre-emergent products indicate that it is a good practice to water the lawn a few days after application in order to wash off the concentration into the soil.

In case it does not rain 2 to 3 days after application, ensure that you apply water on the herbicide as per the instructions on the product’s label.

What month is best to put down pre-emergent?

Most crabgrass seeds will start to germinate in late spring through to mid-summer. This is when the soil temperature of your lawn is between 60 and 70°F. This may, however, be affected by other factors such as wind, shade in your lawn and the general climate of where you live.

Therefore, it is best to put down crabgrass preventer in the month of April. If you are late, you can still do this in early May.

This information is usually supplied by the manufacturer of the product you are using as a herbicide to prevent weeds in your lawn. For example:

Apply in early spring to prevent the germination of crabgrass, chickweed, poa annua, and other common lawn weeds before they start to spread. Apply before the 3rd or 4th mowing to protect all season long. Scott’s Turf Builder Halts Crabgrass (label).Scott's

Read the label

The best way to determine a good time to put down a pre-emergent herbicide for preventing weeds such as crabgrass, foxtail and goosegrass is to read the label of your preferred herbicide.

Each manufacturer recommends the best time to apply for the best result. Some products will give you season-long control of lawn weeds while others provide short-term solutions and probably spaced-out applications

“Barricade can even be applied in the fall for crabgrass control the next season. Dimension can be applied as early as March 1.”Kansas City

If you are not a very experienced at caring for your turf, I would recommend that you try these long-term solutions for preventing and getting rid of unwanted weed grasses in your lawn.

Gauging the effectiveness of preventers

So far, we can categorize these herbicides as short and long residual preventers. Your current problem and level of experience may determine which one you should choose as a pre-emergent solution.

Short residual pre-emergent

These usually last for about 60 days after application. Though the best time to apply may depend on the weather pattern, the best time to apply crabgrass preventers with short-lived effectiveness should be around Mid-April.

Examples of short residual preventers on the market today include Scotts Halts, Team and Tupersan Crabgrass Control.

Long-term residual preventers

If you have no idea how to time the application of a grass weed preventer, I would recommend you go with the long-term solutions. A single application of these herbicides will rid your lawn of crabgrass throughout the season.

The best examples include Barricade and Dimension. You can apply any one of these earlier than the timing of the short-term options. The effect will last throughout the season.


Q: Can I use pre-emergent to kill existing weeds?

It is a rule of the thumb that most pre-emergent herbicides do not get rid of existing weeds. This goes for Scott’s Turf Builder Halts Crabgrass and Barricade – the most popular preventers.

However, Dimension can be used when crabgrass is still very young (about two leaves young).

Should you apply preventer wet grass during the rainy season?

This will depend on the specific product you are using. For example, Crabgrass Barrier indicates on its label that you should apply on wet grass.

When should I water after applying crabgrass preventer?

If it does not rain a few days after application, it is a good practice to water your turf 2 to 3 days afterward. This will wash the herbicide off the leaves into the soil where it will prevent the germination of grass weeds.

2 thoughts on “When to Apply Crabgrass Preventer (Timing Before or After Rain?)”

  1. It doesn’t grow thick in shady areas. It would also need plenty of soil moisture to keep it actively growing when crabgrass season has begun.

Leave a Comment