Crabgrass is a tough grassy weed that can be successfully controlled with an excellent pre-emergent herbicide applied correctly. Crabgrass germinates as the weather warms up in the spring. So, when to put down the crabgrass preventer?
When to apply crabgrass killer is most often during early spring. However, there is more to it than time for your pre-emergent herbicide application.
Soil temperatures must be at certain levels, and typically, lawn treatments work correctly when applied before any heavy rain. However, it is also essential to check pre-emergent product labels as some can withstand rain better than others.
It’s important to remember that a crabgrass pre-emergent herbicide won’t prevent the weed’s germination cycle. Instead, it stops crabgrass from growing roots, allowing your grasses’ natural growing process to outgrow and destroy the weeds.
In our guide, you can learn more about how to stop weed seeds of broadleaf weeds. By the end, you’ll see when and how to apply pre-emergent herbicides and most of all, what a difference rain makes after application. (Learn How Do You Tell A Bermuda Grass Runner From A St. Augustine Grass Runner)
Can You Put Pre-Emergent Down On Wet Grass?
Water must transport pre-emergent into the soil to be effective as a weed barrier. If the earth is damp, it may be unable to absorb any additional moisture. This could cause pre-emergent to break down and run off your lawn instead of being absorbed when sprayed in damp weather.
While at all possible, avoid going out if it’s raining. Pre-emergent applications should be made while the lawn is dry. The soil should not be saturated, even if it is moist.
The herbicide’s effectiveness will be maximized if the timing and application of the pre-emergent are done correctly.
- Soil temperature over 55℉ for three consecutive days during spring.
- Dry or moist grass.
- Your grass is short, or you have recently mown your lawn.
- Rain has been forecast for the upcoming three days.
Because of these optimum conditions, you’ll be able to apply your pre-emergent at the right time to prevent most spring weeds and crabgrass.
These dry conditions also ensure that the soil absorbs the herbicide whenever rain hits. If there is no rain, water the pre-emergent in with a sprinkler for 30 minutes after application.
How Long Does Pre-emergent Need To Be Down Before It Rains?
Surfactants are used in several pre-emergent herbicides to assist them in clinging to leaves. 3-4 hours before the first signs of rain, spray the product on crabgrass and other common lawn weeds.
It works only when the water pulls the pre-emergent down into the soil. Applying pre-emergent to dry grass and then watering the lawn is the best way to accomplish this.
The pre-emergent dissolves in water, and the dry soil absorbs all moisture. If your lawn is already moist, it may not absorb additional water. The pre-emergent may disintegrate and then wash away as runoff.
Pre-emergent should be used before, but not during, or immediately after, rain. This is because pre-emergents sprays in severely wet weather are more likely to wash off saturated soil than penetrate it. As a result, your pre-emergent may get swept down the gutter if you apply it when it’s raining. (Learn How Long Before Rain Can You Spray Roundup)
The wet ground may lose water, resulting in runoff. When it rains, pre-emergent may be washed away.
Maintain your dryness and wait until the rain has stopped. Then, spread your pre-emergent and water it in once the grass and earth are ready for extra water.
Pre-emergent applied in damp conditions will merely be washed away by rain. However, if you apply pre-emergent when the grass is dry, the herbicide will be watered into the soil, where it will build a barrier that will kill seeds as they sprout.
Pre-emergent soaked into the soil can last up to three months. Pre-effective emergent’s lifespan is shortened by significant rainfall. It’s made to tolerate rain and moisture without losing its effectiveness.
- Water your lawn after applying pre-emergent to pull the herbicide into the soil.
- After applying the pre-emergent, water it within 1–3 days.
- It will be enough to water the pre-emergent in if at least 1/2 inch (1.25 cm) of rain is expected.
- If there is no rain, use a sprinkler to apply 1/2 inch of water to wet grass fully and wash the pre-emergent into the soil. (Around 30 minutes).
Like a sponge, dry earth absorbs water, which is perfect for pre-emergent herbicides. To work, pre-emergents and crabgrass preventers must be dissolved in water and soaked into the soil, so apply them while the lawn is dry. Then, to ensure that the herbicide is properly absorbed, add water.
Note: Don’t make the mistake of applying to newly seeded lawns as the natural growing process of grass will be disrupted, and any existing weeds can grow without interruption.
What Month Do You Put Down Pre-emergent?
Pre-emergent timing must be spot on, but how can you know when to apply crabgrass preventer?
Remember that pre-emergent application for weed control will prevent weed seeds from sprouting, but the herbicide barrier won’t control existing weeds.
Here are some tips to help you with your timing:
Crabgrass grows from seeds that fall to the ground in the summer or fall. These seeds remain dormant in the soil throughout the winter, sprouting when the temperature warms up – in the spring.
Apply a pre-emergent herbicide in the early spring to prevent crabgrass from sprouting in your lawn, as this is when the weed will sprout.
Anytime between late March and early April is ideal for applying pre-emergent herbicides like Snapshot to provide all-season protection.
Dogwoods and Forsythia
Forsythia blooms from March to April. After a long, frigid winter, the temperatures increase. If you observe a cascade of bright yellow forsythia flowers, it’s time to lay down crabgrass preventer herbicide for your weed control. If your community lacks forsythia shrubs, dogwoods might be used as a substitute.
Dogwoods bloom from late March to mid-May and have fragrant white blossoms. However, you may still use a pre-emergent herbicide to discourage crabgrass from growing in your lawn when you see these blossoms. (Read Weed B Gon Instructions Rain)
February – Early April
The spring calendar is another excellent indicator of putting down crabgrass pre-emergent herbicide. Spring doesn’t start on the same day every year, so it’s important to look at a seasonal calendar to figure out when to apply crabgrass-preventer weed killer.
Note: If you apply crabgrass preventer too early, it can break down or weaken, making it ineffective at preventing the germination of crabgrass, grass seeds, and other stubborn weeds.
One thing many gardeners overlook is the winter weeds that can spring up. To prevent winter weeds like spurge, henbit, chickweed, and poa-annua, fertilize Bermuda grass with pre-emergent in the early fall of September.
What Temperature Should It Be To Apply Pre-emergent?
Because the sun’s heat heats 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, generally 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 soil temps daily. To limit the root development of the germinating crabgrass seeds, apply crabgrass pre-emergent weed control when the soil temperature is around 55°F. This will help in controlling this persistent grass weed all season long.
Most annual weeds, such as crabgrass, grow in the spring. During this season, the temperature of your lawn’s soil temperatures warm and provides the right environment for germinating weed and grass seed. Some pre-emergents are ineffective at preventing weeds and allowing a few seeds to start germinating. Because of this, some gardeners wonder about the addition of a preemergent herbicide.
However, applying a contact herbicide simultaneously as a fertilizer or pre-emergent is not recommended. The herbicide will be washed away by the water used to apply the fertilizer or pre-emergent or rain wash, and too much soil moisture has the same effect and can wash the pre-emergent away.
As a result, contact herbicide can be applied a day before or after to help prevent weeds.
When to apply crabgrass preventer tips:
- Season – apply in the early spring after new grass has germinated (may vary based on climatic zone)
- Soil temperatures rise to more than 55 °F
- Use the proper timing according to the weather forecast for rain. If it doesn’t rain, water your lawn immediately or 2 to 3 days after adding pre-emergent to ensure the water pushes the pre-emergent into the soil.
- Crabgrass is an annual weed spread via seed and developing roots rather than rhizomes. Check pre-emergent herbicide product labels to stop crabgrass seeds from germinating, as killing full-grown weeds is tough.
Scotts Halts recommends using a crabgrass preventer, such as a pre-emergent herbicide, early in the spring to prevent crabgrass, poa annua, chickweed, and other lawn weeds from germinating in your yard.
The recommendation is to apply crabgrass preventer to your lawn before the third and fourth mowings of the season to keep weeds at bay.
Scotts Crabgrass Preventer contains lawn food, so it will nourish your new lawn while also reducing the need for fertilizer.
Keep in mind that the quantities of nitrogen in this Crabgrass preventer and lawn food are 30-0-4 when you apply fertilizer with this herbicide, so there’s plenty of nitrogen to help your lawn spread and grow thick grass blades.
Short residual pre-emergent: This crabgrass preventer can last up to 60 days after application. It’s better to seed your grass after this time has passed. Apply the herbicide as soon as spring arrives. (Learn How To Get Rid Of Fungus On Tree Stump)
Long residual crabgrass preventers: Long-term crabgrass preventers keep crabgrass at bay for the entire season. To control crabgrass all season long, only use on lawns that are already established.
2EW Dimension Herbicide is a water-based herbicide that controls crabgrass over time, whereas Scotts Halts are short-term pre-emergents that stop crabgrass seed germinating.