Lawn weeds fall into two camps. Cool-season weeds (like annual bluegrass) sprout in fall as the soil cools and run through winter and early spring. Warm-season weeds (like crabgrass) wait for spring soil to warm and take off in summer. Because the two groups germinate at opposite times, controlling them on a Gulf Coast lawn means two pre-emergent windows a year — fall and spring — not one.
It comes down to the soil temperature each weed's seed needs to germinate. Cool-season species germinate fastest at moderate temperatures — roughly the 50s to 60s F — while warm-season species won't get going until spring soil climbs into the mid-50s to low-60s F.
Annual bluegrass (Poa annua) is the signature cool-season lawn weed. A multi-year study found its sharpest flush of seedlings arrives in early-to-mid fall, when the 7-day average soil temperature drops to about 65 F. While your warm-season lawn slides into dormancy, these weeds are just waking up — which is why a dormant winter lawn can look overrun with green weeds.
Crabgrass and other warm-season weeds stay dormant all winter and begin germinating as spring soil temperatures climb back into the 60s F and above. By the time it feels like summer, they're already established — so the window to prevent them is the spring warm-up.
Because the two weed groups germinate at opposite ends of the year, a single annual treatment always misses half the problem. EnSec times treatments to the soil: a fall pre-emergent before soil cools to the high 60s F, a spring pre-emergent before soil warms through the low 60s F, and targeted post-emergent for weeds already up.
What is the difference between cool-season and warm-season weeds? Cool-season weeds germinate when soil cools in fall; warm-season weeds germinate when soil warms in spring. They need pre-emergent at opposite times of year.
When should I apply pre-emergent for winter weeds? Before soil temperatures drop into the high 60s F (around 19 C), typically early to mid fall.
When do summer lawn weeds like crabgrass start growing? As spring soil climbs into the 60s F and above. A spring pre-emergent applied before that warm-up prevents them.
Why is my lawn full of weeds in winter? Mild winters let cool-season weeds thrive while warm-season turf is dormant, so they stand out. Fall pre-emergent plus targeted post-emergent keeps them down.
Want a professional to take a look? Learn about our lawn care service, call 251-210-7263, or request a visit online.
EnSec Pest & Lawn is a family-owned pest control, termite, and lawn care company founded in 1997, with offices in Cantonment and Panama City Beach, Florida, and Mobile and Foley, Alabama. Our team includes Certified Pest Control Operators in Florida and Alabama and an Associate Certified Entomologist, and we are members of the National Pest Management Association with an A+ rating from the Better Business Bureau (License #2004227). This article was written and reviewed by the EnSec team and last updated September 2026.
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