Learn which plants thrive in your Hardiness Zone with our new interactive map!

Weed Killer for St. Augustine Grass

By Robert W. Lewis ; Updated September 21, 2017

St. Augustine grass is a popular turfgrass in tropical and warmer subtropical regions. It is native to the Gulf Coast of North America and is the most widely planted lawn grass in Florida. While weeds are not often a big problem with this warm-season grass, their presence requires quick attention by the homeowner. When weeds encroach upon your St. Augustine grass lawn, finding the right weed killer will help restore its beauty.

Plant Description

St. Augustine grass grows in many soil types and has good salt tolerance. It requires full sun, but some varieties are shade tolerant. St. Augustine grass needs irrigation during drought or it will turn brown. It grows from runners and is easily established from sprigs, plugs or sod. It has an average need for fertilizer among turf grasses.


Healthy St. Augustine grass is not usually plagued by weeds because its thick turf chokes out competition. When weeds do manage to take hold, they are no different from the weeds found in most other lawn grasses. Grassy weeds, such as crabgrass are not unusual. Broadleaf weeds, like clover and plantain are also seen.


Control crabgrass in St. Augustine grass with a pre-emergent herbicide before seeds germinate in the spring. Timing is important since pre-emergent herbicides don’t kill actively growing weeds. Application can be completed as early as February 1 in southern Florida or as late as March in its northern limits. Products containing pendimethalin, benefin or bensulide are effective in controlling crabgrass. Follow label instructions. Post-emergent chemical control of crabgrass in St. Augustine grass lawns is not recommended because it can damage the turf grass.

Broadleaf Weeds

Use a post-emergent herbicide to control broadleaf weeds as they appear. Products containing atrazine are effective. Don’t apply these products to St. Augustine grass that is under drought stress, and don’t apply in temperatures over 85 degrees F, or damage may occur. Always apply according to label instructions. Be careful not to get the spray onto desirable plants because it will damage or kill them.


Maintain St. Augustine grass's health to keep weeds in check. Fertilize regularly and keep the turf watered during drought to keep it thick and healthy. Weed seeds will find it hard to germinate and seedlings will be choked out under these conditions. When weeds appear, take care of them quickly to prevent them from setting seed.


About the Author


Robert Lewis has been writing do-it-yourself and garden-related articles since 2000. He holds a B.A. in history from the University of Maryland and has training experience in finance, garden center retailing and teaching English as a second language. Lewis is an antiques dealer specializing in Chinese and Japanese export porcelain.