Should You Use Weed and Feed on St. Augustine Grass?
Is weed and feed safe for St. Augustine grass? What to look for on the label, why feeding and weeding work better separately, and a month-by-month schedule.
The short version
- Weed-and-feed combines fertilizer and weed killer in one bag. It sounds convenient, but the timing for each job is different.
- It spreads herbicide over the whole lawn, including the 90% that has no weeds.
- Many weed-and-feeds aren't labeled for St. Augustine, and some ingredients can damage it.
- Better: pre-emergent at the right time, spot spray weeds you see, and fertilize on its own schedule.
The timing problem
Fertilizer goes down when the grass is ready to use it: after spring green-up, when the lawn is growing and needs mowing. Weed control works best at completely different times: pre-emergent before weeds sprout in late winter and fall, and spot sprays while weeds are young.
A weed-and-feed forces both onto one date. Put it down early for the weeds, and you're feeding a lawn that's still asleep. Put it down later for the grass, and the weeds are already big and harder to kill.
The whole-lawn problem
Most lawns have weeds in a few spots, not everywhere. A weed-and-feed spreads herbicide across every square foot. That's more chemical than you need, more stress on the grass, and more cost.
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The St. Augustine problem
St. Augustine is more sensitive to some herbicides than other lawn grasses. Plenty of weed-and-feed products on the shelf are made for other grasses, and some ingredients common in them can yellow, stunt, or damage St. Augustine, especially in warm weather. If you do use one, the label must specifically list St. Augustine.
What to do instead
- Pre-emergent by February 1 and again in fall. See pre-emergent for St. Augustine.
- Spot spray weeds that get through with a product labeled for St. Augustine. I spot spray with Southern Ag Atrazine. See safe weed killers.
- Fertilize on the lawn's schedule, once it's actively growing. See when to fertilize in spring.
It's three steps instead of one, but each happens at the right time, and you use less product overall.
A better weed-and-feed schedule for St. Augustine
Here's the same two jobs, each on its own timing, for the Houston and Gulf Coast area:
| When | Weed | Feed |
|---|---|---|
| By February 1 | Spring pre-emergent | Nothing yet. The lawn is still dormant. |
| April, after green-up | Spot spray young weeds on mild days | First fertilizer once you've mowed twice. See when to fertilize. |
| Early May | Second pre-emergent round | — |
| Summer | Spot treat only, and only below the label's heat limit | Light feedings per your plan |
| Early October | Fall pre-emergent | — |
| Early November | — | Low-nitrogen, high-potassium fall fertilizer |
| December–February | Spot spray winter weeds and stickers | None while dormant |
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If you still want a weed-and-feed
- Find "St. Augustine" on the label. Many weed-and-feeds are made for other grasses. Atrazine-based "Southern" formulas are the ones usually labeled for St. Augustine.
- Apply in spring after green-up, when weeds are small and the grass is growing. Not on a dormant lawn.
- Respect the temperature limit on the label. St. Augustine is easily injured by herbicides in summer heat.
- Skip new sod and stressed, drought-hit turf.
- Water it in only as the label says. Some products need the granules to sit on wet weed leaves first.
Common questions
Is weed and feed safe for St. Augustine grass?
Only products whose label lists St. Augustine. Many weed-and-feeds are made for other grasses and contain ingredients that can injure St. Augustine, especially in hot weather.
When should I put weed and feed on St. Augustine?
If you use one, apply it in spring after the lawn has greened up and you've mowed a couple of times, when weeds are small and temperatures are below the label's limit. Never on a dormant lawn or new sod.
What's better than weed and feed for St. Augustine?
Pre-emergent by February 1 and again in May and October, spot spraying weeds that get through, and fertilizing on the lawn's own schedule. Each job happens at the right time and you use less herbicide.
Everything in my St. Augustine program
The fertilizers, weed killers, fungicides, and tools I actually use on my own lawn, with links to buy.