Poa annua pre-emergent (warm-season)
Block winter annual weeds as the soil cools to about 21 °C. Skip it if you plan to overseed ryegrass for winter color.
- When
- Sep 1 – Sep 30 (northern hemisphere) · Mar 1 – Mar 30 (southern)
- Material
- pre-emergent herbicide
- For
- Warm-season lawns (Bermuda, Zoysia, St. Augustine)
- Rule
- wm-poa-preemergent · Walheim; Scotts; Turgeon
Block winter annual weeds (annual meadow-grass) as soil cools to ~21 °C. Skip this if you plan to overseed ryegrass for winter colour — the pre-emergent would block it too.
Why autumn
When a warm-season lawn goes brown and dormant, annual meadow-grass (Poa annua) and winter broadleaf weeds such as henbit and chickweed germinate into the open turf. They show up as bright green clumps in a brown lawn all winter and leave gaps when they die in spring.
When
As soil temperature at 5 cm (2 in) falls to about 21 °C (70 °F), usually in September in the northern hemisphere, March in the southern. Apply before the first winter weed seedlings appear.
How
- Use a pre-emergent herbicide authorized for warm-season lawns in your country, at the label rate.
- Water it in as the label directs.
- Do not aerate or dethatch afterwards.
The trade-off
The same barrier stops perennial ryegrass seed. If you want a green lawn in winter by overseeding ryegrass, skip this pre-emergent; the two are mutually exclusive.
Sources
- Lance Walheim — Lawn Care For Dummieswalheim
- Scotts — Lawnsscotts
- A.J. Turgeon — Turfgrass Managementturgeon