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Learn Your Lawn: Crabgrass in St. Augustine Lawns

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What Is Crabgrass?


Crabgrass is a troublesome annual weed grass that germinates in the spring when soil temperatures are between 54˚F and 56˚F. Crabgrass favors sandy soils and hot, dry areas of your lawn that have thinned and along sidewalks and driveways. Crabgrass does not blend well with most other desirable grasses and can be very invasive if not dealt with appropriately. Once established, crabgrass can take several years to get under control.


Crabgrass will not begin to germinate until early summer. It will have a lime green color and will look similar to a miniature corn plant. Because it’s an annual plant, it will die off in late summer, turning a purplish color and leaving its seed heads to germinate the following year.


How Can I Control Crabgrass In My St. Augustine Lawn?


Crabgrass is not controllable with standard broadleaf weed control products. Keep in mind that ongoing maintenance is crucial for eliminating Crabgrass. If Crabgrass becomes a problem in your St. Augustine lawn, pre-emergent applications can be applied in the fall and spring to help reduce the spread.


A thick, healthy, well-maintained lawn is always the best line of defense. This can be achieved through beneficial cultural practices, which include:

  • Core Aeration: Aerating your lawn can improve soil drainage and help reduce the likelihood of lawn diseases. This will also alleviate soil compaction and allow water and nutrients to penetrate deeper into the soil.

  • Fertilize Regularly: Regular applications of Weed Man’s specially formulated, slow-release granular fertilizer will help provide your lawn with adequate nutrients. These applications are timed specifically to avoid over fertilizing the lawn.

  • Watering: Under normal circumstances, you should be watering your lawn a few times per week for 30-45 minutes in each area. During hot and dry periods, most lawns should be watered as much as required to maintain its desired green color. Always water in the early morning so the turf has time to dry by nightfall.

  • Mowing: Maintain a regular mowing schedule with a razor sharp blade. Never remove more than a ⅓ of the grass blade at each mowing.

Recommended Mowing Height

Common Bermudagrass - ¾ to 1¼ inches

Hybrid Bermudagrass - ½ to 1½  inches

Centipedegrass - 1 to 2 inches

Zoysiagrass - 1 to 2½ inches

St. Augustine - 3 to 4 inches

Fescue - 3 to 4 inches


Your local Weed Man professional will be able to offer other solutions and recommend the best form of treatment that is suitable to improve the conditions of your lawn.