How to Get Rid of Weeds in St. Augustine Green Grass


St. Augustine grass grows well in moist, coastal regions. It thrives in mild winters and hot summers, but does not do well in freezing temperatures. While it can grow in moderate shade, too much shade will make the turf thin and spindly. St. Augustine grass prefers soil with a pH between 5.0 and 8.5. it doesn't deal with traffic well but makes a great lawn. It usually crowds out most weeds but there are several that can invade St. Augustine grass, especially if the grass is weakened by disease or pests. With some care and treatment, you can get rid of them and make your lawn lush and manicured.

Step 1

Spray a pre-emergence herbicide formulated for St. Augustine grass to deal with grassy weeds that pop up every year. This includes crabgrass, fescue and annual bluegrass. Apply it, as per manufacturer's instructions, in the very early spring before the start of new growth.

Step 2

Use hormone-type weed killers to eliminate cool season weeds. Chickweed, henbit and clover are a big issue for St. Augustine grass in the wintertime. Apply the herbicides in early spring.

Step 3

Get a post-emergence herbicide that contains two or more chemicals aimed at killing perennial grasses. Bermudagrass and dallisgrass can be difficult to control. Spray the specialized products directly on the weeds in the early spring.

Step 4

Spray herbicides on the weeds before it gets too hot outside. You may experience a slight discoloration in the St. Augustine grass, which is normal. Reapply every two to three weeks.

Step 5

Treat spaghnum moss with ferrous sulfate (Copperas). Load it into a fertilizer spreader and apply it to the entire lawn. This will help make the grass greener. Use 8 oz. per 1,000 square feet.

Step 6

Add 1/4 lb. of urea per 1,000 square feet. The iron will make the grass greener and help remove moss.

Step 7

Set your mower to the highest wheel setting. Keep the grass 3.5 to 4 inches tall for the more manicured appearance. Shorter grass will invited pests, suffer from stress and result in more shallow root spread.

Tips and Warnings

  • Do not apply herbicides in high temperatures. Even if the label says it can be down, the weed killer can damage to St. Augustine grass. Never apply herbicides in windy conditions because of drift. Avoid spraying near gardens.

Things You'll Need

  • Pre-emergence herbicide
  • Post-emergence herbicide
  • Fertilizer spreader
  • Ferrous sulfate (Copperas)
  • Urea
  • Mower


  • Texas A&M University: St. Augustine Grass
  • University of Florida: IFAS Extension: St. Augustine Grass for Florida Lawns
  • Texas A&M University AggieTurf: Weed Control in St. Augustine Grass
Keywords: St. Augustine grass, Saint Augustine grass, grass and weeds

About this Author

Kelly Shetsky has been a broadcast journalist for more than 10 years, researching, writing, producing and reporting daily on many topics. In addition, she writes for several websites, specializing in medical, health and fitness, arts and entertainment, travel and business. Shetsky has a Bachelor of Arts in communications from Marist College.