Pre-emergent for warm-season lawns

Why before green-up

Warm-season grasses such as Bermuda, Zoysia and St. Augustine stay brown and dormant into spring, while crabgrass and other summer annuals germinate as soon as the soil warms. A pre-emergent applied at that point stops the weed seedlings before the lawn wakes up and can compete.

When

Apply when soil at about 5 cm (2 in) deep reaches 10–13 °C (50–55 °F), usually in March in the northern hemisphere and September in the southern. Forsythia bloom and the first flush of spring growth on hedges are good field signs. In warm climates with a long season, a second application about eight weeks later extends the barrier; follow the label.

How

• Use a pre-emergent herbicide authorized in your country, at the label rate.
• Spread evenly and water it in as the label directs.
• Do not scalp, aerate or dethatch for several weeks afterwards; breaking the surface breaks the barrier.

Not with seed

The barrier also stops grass seed. If you plan to sow or overseed in late spring, skip the pre-emergent that year; see sowing warm-season grass.