The dilemma of dealing with a crabgrass infestation often begins with a fundamental choice: manual removal or chemical treatment. Crabgrass is a frustrating summer annual weed that aggressively competes with desirable turfgrasses for sunlight, water, and nutrients. This fast-growing weed typically emerges in late spring and rapidly takes over thin or damaged lawn areas. The decision depends on the severity of the infestation, the time of year, and the homeowner’s long-term lawn care goals. This guide will detail identifying this weed and exploring options for both immediate removal and lasting prevention.
How to Identify Crabgrass
Crabgrass is easily distinguishable from many desirable turf species by its coarse texture and lighter, often yellowish-green coloring. It is a warm-season grass, classified as a C4 plant, which allows it to thrive in high temperatures and intense sunlight when many cool-season turf varieties are under stress. The name comes from its distinct growth habit, which is low to the ground and sprawling, with stems radiating outward from a central point like the legs of a crab.
The leaves are typically wide and slightly rough to the touch. For the most common species, large crabgrass (Digitaria sanguinalis), the leaves are often covered in dense hairs. Later in the season, the plant produces distinctive seed heads that resemble thin, finger-like spikes clustered at the top of the stem. Since crabgrass is an annual plant, it completes its life cycle by producing thousands of seeds before the first hard frost kills the plant.
Manual Removal: Technique and Drawbacks
Hand-pulling is a highly effective control method for small, isolated patches of crabgrass, especially when the plants are still young seedlings. For this technique to be successful, it is important to remove the entire fibrous root system to prevent regrowth. Pulling the weed when the soil is moist helps ensure the entire plant, including the roots, is extracted cleanly and completely.
However, relying solely on manual removal for a widespread infestation presents significant drawbacks. Crabgrass plants are prolific seed producers, with a single plant capable of generating up to 150,000 seeds. If the plants have already set seed, pulling them can inadvertently scatter viable seeds across the lawn, effectively seeding the next season’s crop.
Another disadvantage of manual removal is the disturbance of the soil surface. Whenever a weed is pulled, the exposed soil creates a perfect environment for dormant crabgrass seeds to germinate. These seeds can remain viable for several years. Pulling a large, mature plant can create a bare spot that is quickly filled by a new flush of seedlings later in the season. Therefore, manual removal is best reserved for early-season spot treatment before the plant begins its reproductive stage.
Choosing the Right Herbicide
For larger infestations where manual removal is impractical, chemical control offers a more efficient solution. Crabgrass herbicides fall into two main categories, distinguished by how they function in relation to the weed’s life cycle.
Pre-emergent herbicides create a chemical barrier on the soil surface that prevents the crabgrass seeds from successfully germinating. Timing is paramount, as they must be applied before the seeds sprout. Germination begins once the soil temperature consistently reaches 55°F at a shallow depth for four or five consecutive days. Applying the pre-emergent product just before this temperature threshold ensures the protective barrier is in place when the seeds begin to grow. After application, the herbicide must be watered into the soil to activate the chemical barrier.
Post-emergent herbicides are used after the crabgrass has already emerged and is actively growing. These products are most effective when the weed is still small, ideally in the two- to five-leaf stage, or before it has developed more than four tillers. As the crabgrass plant matures, it becomes increasingly difficult to control, often requiring multiple applications spaced two to three weeks apart. Products containing active ingredients like quinclorac or mesotrione are typically used for post-emergent control.
Long-Term Prevention Strategies
The most effective long-term strategy against crabgrass involves establishing a dense, healthy turf that naturally outcompetes the weed. Crabgrass thrives in thin areas and bare spots, so promoting thick turf growth is the best defense.
Proper mowing height plays a significant role in prevention because the seeds require adequate light and warm soil temperatures to germinate. Mowing the lawn at a higher setting (typically between 2.5 and 3.5 inches depending on the turf type) allows the grass blades to shade the soil. This shading action keeps the soil cooler, which directly inhibits the germination of crabgrass seeds. Additionally, deep and infrequent watering encourages the turfgrass to develop a deep, robust root system, avoiding the shallow, frequent moisture conditions that favor crabgrass growth.
Overseeding the lawn, particularly in late summer or early fall, is another preventative measure that minimizes crabgrass recurrence. As the annual crabgrass dies off with the first frost, it leaves behind bare patches that are easily colonized by new seeds the following spring. Filling these voids with desirable turfgrass seed ensures that the ground is covered, blocking the sunlight and space that crabgrass needs to establish itself.