Pre-emergent herbicides are a powerful tool to control crabgrass and other weeds, but using them correctly is key to maximizing their effectiveness and minimizing harm to your lawn. Early spring is the best time to apply a pre-emergent herbicide as long as you don’t plan to plant new grass or overseed.
What is Pre-Emergent Herbicide?
Unlike post-emergent herbicides that target existing weeds, pre-emergent herbicides form a barrier in the soil that disrupts the germination process of weed seeds. This prevents new weeds from taking root, keeping your lawn looking its best. For this reason, you shouldn’t apply pre-emergent if you plan to overseed or plant new grass in the spring, it will prevent the seed from growing.
Here are some popular pre-emergent herbicides:
- Prodiamine: This granular formula is effective against crabgrass, foxtail, and many other grassy weeds. It’s suitable for most cool-season grasses. It doesn’t contain fertilizer which is a good option if you don’t want to feed your lawn this early in the season.
- Dimension: Similar to Prodiamine with the main difference being that it’s more water-soluble, it has a tendency to leach out quicker in early spring applications, in other words, may not last as long. This does include some fertilizer to feed the lawn.
- Scotts Turf Builder Halts Crabgrass Preventer w/ Lawn Food: This combination product combines fertilizer with a pre-emergent that prevents crabgrass and other grassy weeds.
Preparing Your Lawn for Application
Before applying a pre-emergent herbicide, it’s important to prepare your lawn:
- Measure your lawn: this is crucial so you know how much product to apply. I go over some different ways you can measure your lawn here.
- Clean Up: Remove any debris from your lawn. This ensures the pre-emergent reaches the soil where weed seeds germinate.
- Timing is Key: Apply the pre-emergent according to the manufacturer’s instructions and within the recommended window. Spring application typically occurs when soil temperatures are between 50-55°F, while fall application happens before the first frost.
Four Ways To Know When To Apply Pre-Emergent In Early Spring
- Soil Thermometer – when soil temperature is 50°F and trending up
- Forsythia Bush – yellow bush, when it begins to bloom
- Greencast Online – enter your zip code to get soil temperature in your area
- GDD Tracker – enter your zip code to get the optimal time to apply pre-emergent
Although it’s more effective when applied at the optimal time, it’s ok if you’ve missed it. It’s better to apply pre-emergent a little late than nothing at all.
Applying the Pre-Emergent Herbicide
Once you have the right product and your lawn is prepped, it’s time for application:
- Read the Label Carefully: Every product is different, so ensure you understand the application rate, safety precautions, and any specific instructions for your chosen pre-emergent.
- If the application rate isn’t listed, take the weight of the bag and divide it by the square footage it covers so you know how many pounds of product is required per 1,000 sqft. For example, if the bag weighs 10lbs and covers 5,000 sqft, do 10/5 and you get 2lbs. per 1,000 sqft.
- Application: Typically spread with a rotary spreader, ensuring even distribution.
- Watering: Most granular pre-emergents require light watering after application to activate the product. A good strategy if you don’t have irrigation is to apply the pre-emergent before rain is expected.
Maintaining Your Lawn After Application
After applying the pre-emergent, proper lawn care is essential:
- Watering: Water your lawn deeply and infrequently.
- Mowing: Maintain a regular mowing schedule at the appropriate height for your grass type. This will help prevent weeds from establishing themselves.
- Patience: Pre-emergent herbicides take time to work. Don’t expect them to eliminate existing weeds, but they should prevent new ones from emerging.
- Consider spot treatments: For weeds that emerge despite the pre-emergent, spot treatment with a post-emergent herbicide such as Weed-B-Gon can be effective.
By following these steps and using pre-emergent herbicides strategically, you can keep your lawn healthy and free of weeds, ensuring a beautiful green lawn you can enjoy all season long.
