Crabgrass (Digitaria species) is an annual grassy weed that plagues turf, and summer is the most challenging time for control. This warm-season annual germinates in spring when soil temperatures consistently reach 55°F, growing aggressively throughout the hotter months. By mid-summer, it is a mature, sprawling plant actively competing with desirable turf for water and nutrients. Successfully getting rid of this established weed requires a shift from preventative measures to targeted removal strategies.
Why Summer Control is Challenging
Summer crabgrass is difficult to manage because it has fully matured and developed a high tolerance for stress. As a C4 plant, crabgrass thrives in the intense heat and sunlight of summer, giving it a physiological advantage over many common cool-season turf grasses. This resilience means that treatments must be potent enough to kill the weed without severely damaging the stressed lawn.
The primary preventative tool, pre-emergent herbicide, is no longer effective once the plant is visible above ground. Pre-emergents work by creating a chemical barrier in the soil to stop the germination process, but they cannot kill an established, actively growing plant. By summer, the plant has also begun its reproductive phase, producing seed heads that contain thousands of potential seeds for the next season.
Post-Emergent Chemical Removal
For widespread summer infestations, selective post-emergent herbicides are the most reliable solution for mature crabgrass. These systemic chemicals are absorbed through the leaves and transported throughout the entire plant, including the roots, leading to complete eradication. Since crabgrass is a grass, it requires a specialized product that targets grassy weeds without harming the desirable turf.
The most effective active ingredients for mature crabgrass are Quinclorac and Mesotrione. Quinclorac is noted for its ability to control large, multi-tiller plants, often requiring a second application two to three weeks later for complete kill. Mesotrione is also very effective and is known for turning susceptible weeds white before they die, offering a clear visual confirmation of the treatment working.
Timing the application correctly is important to prevent damage to the lawn, which is already under heat stress. Post-emergent products work best when the crabgrass is actively growing, and application should be avoided when temperatures exceed 85°F. Applying herbicides during extreme heat can cause the product to volatilize or be absorbed too quickly by the turf, resulting in damage. Always use a non-ionic surfactant or methylated seed oil with these products, as recommended by the label, to help the herbicide stick to the waxy crabgrass leaves for better absorption.
Non-Chemical and Manual Methods
For small patches or scattered individual plants, non-chemical and manual methods offer targeted removal without the need for broadcast chemical application.
Hand Removal
Hand-pulling is highly effective for isolated weeds, but it is necessary to grasp the plant at the base and remove the entire root system. If even a small part of the root remains, the plant can potentially regrow, especially in moist soil.
Spot Treatments
Alternative spot treatments can be used on plants in driveways, sidewalks, or small lawn areas where localized damage is acceptable. Boiling water poured directly onto the plant will instantly kill all above-ground tissue, though multiple applications may be necessary to fully eliminate the root. Horticultural vinegar or strong household vinegar (5-10% acetic acid) mixed with dish soap can also be sprayed to scorch the weed. These non-selective acidic treatments will kill any plant they contact, including the surrounding turf, so they must be applied with precision.
Solarization
For larger but manageable patches, solarization involves covering the area with clear plastic sheeting for several weeks during the hottest part of the summer. This process traps solar energy, raising the soil temperature high enough to kill the crabgrass, though it will also kill the underlying desirable grass.
Cultural Practices to Prevent Seed Spread
The ultimate goal of summer control is to prevent the existing mature plants from dropping viable seeds, which can remain dormant in the soil for years. A single mature crabgrass plant can produce up to 150,000 seeds, emphasizing the need to eliminate the plant before it completes its life cycle.
Mowing Height
Adjusting your mowing height is one of the easiest and most effective cultural practices. Raising the mower blade to at least three inches shades the soil surface, which keeps the ground cooler and suppresses the germination of any new crabgrass seeds. Taller turf also encourages a denser canopy, which naturally crowds out the weed.
Watering Practices
Watering practices should also be modified to favor the turf grass over the shallow-rooted crabgrass. Deep, infrequent watering encourages the deep root growth of desirable grass species, making them more resilient to summer drought and heat. Shallow, frequent watering keeps the soil surface moist, which is exactly what crabgrass needs to thrive and germinate new seedlings.
Fertilization and Cleanup
Avoid high-nitrogen fertilization during the mid-summer heat, as this can stimulate the growth of warm-season weeds like crabgrass more than the cool-season turf. By late summer, even if the plant is dying from a post-emergent treatment, physically removing or bagging the seed heads is a necessary step to significantly reduce the seed bank for the following spring.