When to Put Down Pre-Emergence Treatment for Crabgrass in Zone 7

Life Cycle

• Crabgrass is an annual weed that that spreads along the ground. It has hairy stems, broad blades and a tall flower spike with arms that spread out like fireworks. Sowing its seed in the summer heat, it slows down in fall, sometimes turning purple. It then dies when cold temperatures arrive. The tiny seeds lay in wait throughout the winter, then germinate in spring, about the same time the forsythias (Forsythia spp,) bloom in USDA zones 4 to 9.

Pre-Emergent Crabgrass Killer

• Granular pre-emergent crabgrass killer contains a chemical, such as pendimethalin, to prevent crabgrass seeds from germinating in spring. It can be applied to most lawns in USDA zone 7, including tall fescue (Festuca arundinacea) and Kentucky bluegrass (Poa pratensis) and zoysiagrass (Zoysia japonica). Kentucky bluegrass and tall fescue are cool-season grasses that grow in USDA zones 2 through 7, while zoysia, a warm-season selection, grows in USDA zones 5 through 10. Read the product label to make sure it will not harm your grass type. University of Maryland Extension recommends using a product that does not contain fertilizer, "weed and feed," as it often results in overfertilization.

Timing, Timing, Timing

• Just as important to success is when you apply crabgrass preventer. Pre-emergents must be put down before the seed germinates or you'll be facing crabgrass again, come summer. Crabgrass germinates when soil temperature reach 55 to 60 degrees Fahrenheit for seven to 10 days consecutively. In the warmer reaches of USDA zone 7, apply in mid-March to early April. In the cooler areas, your window is approximately the first three weeks of April. Time windows are estimates; if spring comes early or late, you might need to apply it a week or so earlier or later.

Tips for Success

• Even coverage is important for the best results. Use a broadcast spreader or a drop spreader, following application rates on the label. Don't disperse pre-emergent crabgrass granules in flower borders or vegetable gardens, where they can damage plants and prevent the germination of desirable flower and vegetable seeds. If you need to control crabgrass in ground covers, make sure the product is labeled for use on your particular plant.