5 Ways to Know When to Apply Crabgrass Preventer

Apply crabgrass preventer in spring when soil temperatures rise to 55℉ (13℃) for 3 consecutive days. Crabgrass begins to germinate at this temperature and continues to sprout more vigorously as soil temperatures climb to 60–70℉ (16–21℃). Crabgrass preventer remains active in the soil for 2–6 months, so an early application will stop initial crabgrass sprouts and late-sprouting seeds.

@hen to apply crabgrass preventer

5 Tips to Time Crabgrass Preventer Application Perfectly Every Year

Weather patterns shift from year to year. Instead of looking at the calendar to time your crabgrass preventer, time it perfectly by keeping track of soil temperature. This can be done as easily as checking the weather using this free online soil temperature map. Just keep these rules in mind:

Know When Crabgrass Germinates

Each crabgrass seed is essentially a biological thermometer, waiting for nature’s signal to sprout. After crabgrass seeds are dropped in fall, they lie dormant in the soil through the cold months until temperatures climb.

  • Crabgrass is biologically triggered to begin sprouting in spring when the soil reaches an average 55℉ (13℃) for 2–3 days straight.
  • Although early seeds start at 55℉, the majority of crabgrass seeds germinate when soil temperatures reach 60–70℉ (16–21℃).

Once spring comes, keep an eye on weather patterns. A warm spell in March or April may trigger crabgrass seeds to begin growing. In certain years, weather in northern climates may not be ideal for crabgrass germination until late April or early May.

Understand Crabgrass Preventer

Crabgrass preventer belongs to a class of herbicides known as pre-emergents. Once they’re spread on your lawn and watered in, pre-emergents remain in the soil for 2–6 months (depending on the product used). Every weed, grass, or other plant seed that germinates during this time will be attacked and killed before it ever breaks the surface.

  • Crabgrass preventer works by killing seeds as they germinate. For best results, apply when the soil reaches the 55-degree mark.
  • Crabgrass preventer is a pre-emergent herbicide. It won’t kill plants that have already sprouted, so apply early rather than late.
  • Dormant seeds won’t be harmed by crabgrass preventer. It only attacks seeds as they begin to germinate underground.

Crabgrass preventer truly is only a preventative measure. If crabgrass has already sprouted up in your yard, you’ll need to use a post-emergent herbicide to kill it.

Apply Crabgrass Preventer Based on Soil Temperature

The most reliable way to get your spring crabgrass preventer application right every year is to track the soil temperature in your area. The good news is, you can easily measure your soil temperature.

  • Use a soil temperature map or soil thermometer to check soil temperature.
  • Once the average for the past 3 days reaches 55℉ (13℃), it’s time to spread your crabgrass preventer.

This method is the most scientific and accurate way of timing crabgrass preventer application. It’s the top choice for lawn maintenance.

Use Air Temperature as a Fallback

Although it’s slightly less accurate than checking soil temperature, a good rule of thumb is that the soil temperature is about 10 degrees Fahrenheit cooler than daytime air temperatures. If the daytime high is 65℉, the soil is likely at 55℉.

  • Soil temperature is usually 10 degrees Fahrenheit lower than daytime air temperatures.
  • Keep an eye on your local weather forecast as spring approaches—you may be able to plan your crabgrass preventer application a few days in advance.

Using the weather forecast as a signal can remind you to check soil temperatures. It can also help you get a peek at what’s to come and buy all the materials you need to spread pre-emergent in advance.

Keep an Eye on Signal Plants

Other plants in your yard or neighborhood can give you the sign that it’s time to apply crabgrass preventer. This method is less accurate than using soil temperature, and you may not have these plants in your area, but dogwoods, lilac, and forsythia will tell you when it’s time to spread pre-emergent. Apply crabgrass preventer when you see any of these signs:

  • Dogwoods begin to bloom.
  • Forsythia buds appear.
  • Lilac buds are just about to bloom.

These plants are common enough that you may have one of these varieties in your garden. They can operate as benchmarks that signify when crabgrass is about to sprout.

What Crabgrass Preventer Should You Use?

Our top choice for crabgrass preventer products is Barricade. This powerful pre-emergent herbicide remains in the soil for 6 months, which is 2–3 times as long as competitor products. It’s a powerful choice that’s safe for your turf grass.

  • Use Barricade pre-emergent to stop crabgrass.
  • Barricade lasts up to 6 months. Even if you apply early it will stop crabgrass through spring and summer.
  • One application of Barricade stops both crabgrass and summer annuals, like chickweed.

While other pre-emergents may require repeat applications throughout the year to ensure you stop both crabgrass and late-sprouting weeds, Barricade can stop them all with one application. This saves you money and lowers your lawn care workload.

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Cautions for Crabgrass Preventer Use

Always keep in mind that crabgrass preventers are non-selective herbicides. This means they attack all seeds upon germination, including grass seed. If you apply crabgrass preventer in spring, don’t overseed your lawn until fall.

  • While it is active in the soil, crabgrass preventer kills all seeds that attempt to sprout, including turf grass, vegetable, tree, and flower seeds.
  • Spread crabgrass preventer carefully—avoid spreading it in gardens where you plan to plant seeds.
  • Make a note of the date you apply crabgrass preventer. It will remain active in the soil for 2–6 months, depending on the product used.

It’s important to know how long your pre-emergent herbicide lasts. Keep track of the application date of any crabgrass preventer, as well as the effective time span of the product used. This will help prevent damage to desirable grass and plant seeds.

What is the Best Time to Apply Crabgrass Preventer?

When it comes to crabgrass preventer, timing is everything. To time your crabgrass preventer application, follow these quick rules:

  • Apply when soil temperatures rise to 55℉ (13℃) for 2–3 consecutive days in spring.
  • Soil temperatures are typically 10 degrees Fahrenheit cooler than air temperatures.
  • Crabgrass preventer only kills seeds as they sprout underground. It won’t attack visible plants or dormant seeds.
  • It’s better to apply crabgrass preventer early than late.
  • If dogwoods are blooming, or forsythia and lilac are about to bloom, it’s time to apply crabgrass preventer.

The most important thing to know is to ignore the calendar when timing crabgrass preventer application. Weather patterns shift from year to year, so let mother nature tell you when the time is right.

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