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How Do I Kill St. Augustine Grass?

green grass lawn image by jimcox40 from

Whether you are adding a new gardening bed, you are unhappy with the St. Augustine grass or have a lawn-remodeling project, sometimes you are required to kill the grass and remove it. St. Augustine (Stenotaphrum secandatum) is a warm-season grass predominately found growing in the warm coastal regions of the United States. The grass spreads aggressively by above ground runners growing up to 1 inch per day during the warm growing season. Gardeners wishing to eliminate the grass will have success, but it will take up to two weeks for the total eradication of the St. Augustine.

Suspend mowing the St. Augustine grass before you intend on killing it. The longer the grass blades, the more surface the herbicide has to stick.

Water the area of St. Augustine grass thoroughly, for approximately two to three weeks before beginning the eradication process. The water will “plump” the grass blades up, allowing more surface area for the herbicide to work.

Apply lawn fertilizer to the St. Augustine to “plump” it up and get the grass in its healthiest form before beginning the process of killing it. This is not a requirement but allows more blade surface to develop, helping the herbicide work better.

Mark the section of St. Augustine grass you desire to kill, if you will not be killing the entire area. Use a gardening spray paint and spray around the section of grass you wish to eliminate.

Turn off all water to the area of St. Augustine the day before you intend on beginning the process of killing it and keep it turned off. You do not want excess water on the grass that will wash the herbicide off the blades.

Fill a pump-up sprayer with a non-selective grass and weed killer and mix, per the package instructions. Select a herbicide that does not affect the area’s soil long-term, especially if you intend on replanting the area with more grass or other vegetation.

Apply the herbicide early in the morning of a sunny day when there are no winds. Spray the area of St. Augustine grass you are killing, fully saturating the leaf blades. Spraying early in the morning allows the product to fully dry on the grass blades and the sun will quicken the killing process.

Repeat the application of herbicide in approximately three to four days, killing any St. Augustine that is hanging onto life. Do not water the area for approximately two weeks to allow the product to work. The grass should begin to turn brown and die. If green areas remain in the St. Augustine, repeat the application of herbicide to those areas.

Remove the grass two weeks later when it has died and turned brown and no sign of green is left. Dig the grass from the ground being sure to remove the roots.

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