TLDR:
Knowing when to start pre-emergent weed control is key to stopping unwanted weeds before they appear. The ideal time to apply pre-emergent is early spring, when soil temperatures consistently reach around 55°F. This typically occurs between mid-March and early April in climates like northern New Jersey. For fall germinating weeds, a second application in late summer or early fall is recommended. Apply before weed seeds sprout—not after.
Learn When to Start Pre-Emergent Weed Control for Optimal Results
If you’re aiming for a lush, green lawn free from pesky invaders like crabgrass or dandelions, pre-emergent weed control is one of the most effective tools at your disposal. But knowing when to start pre-emergent weed control is just as important as choosing the right product.
Apply it too early, and it may break down before it can stop weed seeds from germinating. Apply it too late, and the weeds may already be sprouting. The key is timing your application before the seeds germinate—but just as they’re about to.
Need help getting your timing right? Contact Borst Landscape & Design or call (201) 254-5732 for expert lawn care services tailored to your property.
What Is Pre-Emergent Weed Control?
Pre-emergent herbicides are products designed to stop weeds before they break through the soil surface. These treatments create a chemical barrier in the top layer of soil, targeting germinating weed seeds as they begin to grow. It’s important to note that pre-emergents don’t kill existing weeds—they prevent new ones from taking hold.
Common weeds that pre-emergents help control include:
- Crabgrass
- Goosegrass
- Chickweed
- Dandelions
- Clover
- Spurge
Timing Is Everything: Watch the Soil Temperature
The most accurate way to determine when to start pre-emergent weed control is by monitoring soil temperature, not the calendar. Most weed seeds begin to germinate when the soil reaches 55°F for several consecutive days at a depth of 1 to 2 inches.
In Zone 6 areas like Bergen County, this typically occurs from mid-March to early April—but it varies depending on winter weather patterns. You can use a soil thermometer or refer to online soil temperature maps to guide your timing.
Spring Application: Controlling Summer Weeds
The spring application is your most important pre-emergent treatment of the year. It prevents the germination of summer weeds like crabgrass, which can spread quickly and crowd out healthy turf.
Tips for Spring Application:
- Apply pre-emergent before or as soon as soil hits 55°F.
- Don’t aerate the lawn after application—it can break the chemical barrier.
- Water in the product after applying to activate it.
- Avoid disturbing the soil surface afterward.
Fall Application: Stopping Cool-Season Weeds
Fall is often overlooked, but just as important—especially for lawns plagued by winter annuals like poa annua (annual bluegrass) and henbit. These weeds germinate in late summer to early fall, so a second round of pre-emergent in August or September can keep them at bay.
When Not to Apply Pre-Emergent
There are a few scenarios where you should avoid pre-emergent use:
- When seeding new grass: Pre-emergents prevent all seeds from germinating, including grass seed.
- If weeds are already visible: Pre-emergents don’t kill existing weeds—use a post-emergent product instead.
- Too early or too late in the season: Applying outside the germination window reduces effectiveness.
How Long Does Pre-Emergent Last?
Most pre-emergent herbicides remain effective for 8 to 12 weeks, depending on the product and weather conditions. This means:
- Spring applications typically protect through late spring and early summer.
- Fall applications last through early winter.
For season-long control, some lawns may benefit from split applications—applying half the recommended dose twice during the germination window.
Common Mistakes to Avoid
- Ignoring Soil Temperatures: Don’t rely solely on the calendar.
- Not Watering In: Without moisture, the herbicide won’t activate.
- Disturbing the Soil: Raking or aerating after application can ruin the barrier.
- Overapplying: Too much pre-emergent can harm beneficial grass and roots.
Additional Lawn Care Tips
- Mow regularly, but not too short. Taller grass helps shade the soil and discourage weed growth.
- Fertilize at the right time. Don’t fertilize too early in spring—wait until grass is actively growing.
- Keep a lawn care calendar. Track your pre-emergent and fertilizer schedule to stay on top of timing.
Final Thoughts
Learning when to start pre-emergent weed control can make all the difference in achieving a weed-free, healthy lawn. The key is timing your application around soil temperature—not the calendar—and ensuring you follow through with proper watering and lawn care practices.
If you want tailored support to keep your lawn looking its best, the professionals at Borst Landscape & Design are here to help. Call us at (201) 254-5732 for expert lawn care that aligns with the unique needs of your property and growing zone.
FAQs: When to Start Pre-Emergent Weed Control
Q: What month should I apply pre-emergent?
In northern climates like New Jersey, the best time is typically mid-March to early April, depending on soil temperature.
Q: Can I apply pre-emergent in the fall?
Yes, fall applications are great for preventing winter annual weeds. Apply around late August to early September.
Q: What happens if I apply pre-emergent too early?
It may break down before weed seeds start to germinate, making it less effective when you need it most.
Q: Can I overseed after applying pre-emergent?
No. Pre-emergent prevents all seed germination, including grass seed. Wait until the herbicide wears off—usually 2–3 months—before seeding.
Q: Do I need to water after applying pre-emergent?
Yes. Light watering or rainfall activates the herbicide and creates the barrier needed to stop weed growth.
Q: Does pre-emergent kill existing weeds?
No, it only stops seeds from germinating. Use a post-emergent product for visible weeds.