Weed control in South Texas is different from the Midwest or the Northeast, and the products and timing that work there can damage your grass here. San Antonio lawns are mostly warm-season turf, St. Augustine and Bermuda, and many herbicides that work fine on Bermuda will damage or kill St. Augustine if applied incorrectly. Before you buy anything, knowing what grass you have and what weeds you're dealing with will save you the cost of a damaged lawn.
Quick answer
Effective weed control in San Antonio depends on timing: pre-emergent applied in late winter to early spring before soil temperatures hit 55 degrees stops crabgrass and other summer weeds before they germinate. Post-emergent products handle what's already growing, but the herbicide must match your grass type or you risk damaging St. Augustine. Dense, healthy turf is your best long-term defense.
Dealing with this right now?
Nutsedge, crabgrass, and winter weeds taking over your lawn? Schedule a lawn care visit with Bob Jenkins Pest & Lawn Services and we'll put together the right weed control program for your grass type and property.
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The Two-Window Approach: Pre-Emergent and Post-Emergent
Pre-emergent herbicides stop weed seeds from germinating. They don't kill existing weeds and have no effect once seeds have already sprouted. Applied at the right time, they're the most efficient tool in the arsenal. Applied too late, they're a waste of money.
Post-emergent herbicides kill weeds that are already growing. They need to reach green leaf tissue to work, so timing application to young, actively growing weeds gives better results than trying to knock back a mature established one. Selective post-emergent herbicides kill the target weed while leaving your grass; non-selective products kill everything green.
Timing Pre-Emergent in San Antonio
The target is applying pre-emergent before soil temperatures reach 55 degrees at a 2-inch depth, which is when crabgrass and many summer annual weeds start germinating. In San Antonio, that typically means applying in February to early March. Soil temperatures can rise quickly here after a mild winter.
A second application in September or October addresses winter annual weeds like henbit, chickweed, and annual bluegrass, which germinate in fall and are actively growing through winter. Many San Antonio homeowners see their worst winter weed problems because they only treat in spring.
- Late February to early March: first pre-emergent for summer annuals (crabgrass, spurge)
- September to October: second pre-emergent for winter annuals (henbit, chickweed)
- Apply before rain is expected to move the product into the soil
- Watering in a granular pre-emergent within 24 to 48 hours of application activates it
The Weeds That Give San Antonio Homeowners the Most Trouble
Crabgrass and goosegrass are the summer annual culprits. They germinate with the heat, fill in thin spots in the lawn, and set seed before the season ends, guaranteeing a worse problem next year. Pre-emergent applied in late winter stops them before they start.
Nutsedge is the one that drives homeowners up the wall. It's not a true weed or grass, it's a sedge, and it shrugs off most standard broadleaf or grass herbicides. Don't pull it. The nutlets you leave in the soil sprout into multiple new plants, so it takes a specialized herbicide containing halosulfuron or imazaquin, applied when the plant is actively growing in warm weather.
Herbicide Safety on St. Augustine Grass
St. Augustine is more herbicide-sensitive than Bermuda. Atrazine is one of the few products labeled for broadleaf weed control in St. Augustine, but it can damage the grass at high rates or during heat stress. Several popular broadleaf herbicides that work fine on Bermuda, like products containing 2,4-D at high concentrations, can severely damage or kill St. Augustine.
Always read the label before applying any herbicide to a lawn containing St. Augustine. Texas A&M AgriLife Extension maintains up-to-date information on safe herbicide use for Texas turfgrass and is a more reliable resource than general lawn care advice not written for this region.
Dense Turf Is the Best Weed Barrier
Weeds get a foothold where the turf is thin. A dense, healthy lawn outcompetes weed seeds by shading the soil and leaving no bare ground for germination. This is why fertilization, proper mowing height (higher for St. Augustine during summer heat), and irrigation management are as much a part of weed control as any herbicide.
Bob Jenkins Pest & Lawn Services provides weed control for San Antonio lawns as part of a complete lawn care program, selecting products appropriate for your specific grass type and the weeds present. The goal is healthy turf that doesn't give weeds an opening, not just repeated herbicide applications to a struggling lawn.