What's the best time to apply weed preventers?
Written by
Tina Carter
Reviewed by
Prof. Martin Thorne, Ph.D.Preventing weeds involves mastery of timing. Soil temperature dictates success; in most areas of the country, you should apply pre-emergents once the soil temperature is about 55°F (13°C). I had a client in Oregon who timed his applications to the local lilac blooms, so he was able to prevent 90% of crabgrass. Find the average frost dates of your area to ensure accuracy!
Soil Temperature Monitoring
- Insert a meat thermometer 2 inches deep for readings
- Mid-Atlantic: Apply when forsythia flowers open
- Southwest: Treat 2 weeks after mesquite leafs out
Organic Alternatives
- Spread corn gluten meal when maple seeds drop in fall
- Use shredded oak leaves as mulch in zones 5-7
- Apply soybean meal in coastal climates to block chickweed
It is a good idea to refresh mulch after the last frost date in your area to control early germinating plants. A client of ours in Tennessee uses pine straw refreshed each May, and she saw a drop in weed pressure of 75%. Volcanic rock mulch should not be used in rainy areas. This mulch will compact over wet seasons and become ineffective after three seasons.
Steer clear of all-too-typical timing mistakes. When you apply your pre-emergents too early, it is wasted. Or, by the time the seeds activate and germinate, the product has already washed away. If you apply too late, you already missed the window for germination. I map my client's yards into micro-zones while using infrared thermometers to note variations in shaded vs. sunny areas.
Pairing corn gluten meal with crimson clover cover crops is effective for organic gardens. The roots of clover release natural herbicides, and it fixes nitrogen as well. One Michigan farmer managed to eliminate 60% of his bindweed using this method. Test your soil to ensure the pH is acceptable below 6.0. pH below that decreases the effectiveness of corn gluten.
Read the full article: How to Prevent Weeds: 12 Expert-Backed Strategies
