Why then
Southern soils cross the crabgrass-germination threshold (~55°F at soil level) early — often by late February along the Gulf. The window here runs the three weeks up to the average last frost, and earlier beats later: pre-emergent that goes down after soil warms is wasted. Skip pre-emergent anywhere you plan to seed this spring; it can’t tell crabgrass seed from grass seed.
Frequently asked questions
When should I apply crabgrass pre-emergent in Louisiana?
Across Louisiana's featured cities the window runs Jan 11 – Feb 28. Your own town can sit at either end of that range — use the city table on this page or the ZIP lookup for your exact dates.
Why do the dates vary within Louisiana?
Because climate does. The dates here are calculated separately for each city from its own NOAA 1991–2020 frost records, and elevation, latitude, and terrain spread them across Louisiana — the same task can be a week or two apart between towns. That local spread is exactly what generic national advice misses.
What if I miss the window?
Pre-emergent after crabgrass has germinated is wasted product — switch plans to post-emergent control on young crabgrass and put the pre-emergent reminder on next year’s calendar instead.