The sudden appearance of rapidly growing, tall patches of grass quickly disrupts a lawn’s uniform texture. These coarse clumps often look conspicuously different, growing faster and wider than the surrounding turfgrass. The culprits are typically aggressive, invasive grass or grass-like weeds, not mutations of the desired lawn species. Identifying these invaders is the first step toward effective removal, as different species require specific control strategies. This article will help homeowners identify these unwanted guests and provide targeted control methods.
Common Invaders and How to Spot Them
One of the most frequent summer invaders is Crabgrass, a summer annual with a light green or yellowish hue and broad, coarse blades. This weed grows low and spreads outward in a star-like pattern from a central point. As an annual, it germinates from seed in the spring when soil temperatures warm and dies completely with the first hard frost, leaving behind a bare patch.
Another common nuisance is the clumping variety of Tall Fescue, a cool-season perennial grass with a coarse texture and a medium to dark green color. Unlike spreading turfgrasses, this fescue is a bunch-type grass, growing in distinct, isolated tufts that stand taller than the rest of the lawn. Because it is a perennial, Tall Fescue clumps persist and return year after year, often greening up earlier than desirable grasses.
Quackgrass is a tenacious perennial grass identifiable by its dull, ashy blue-green color and wide leaves. Its defining characteristic is its aggressive underground network of sharp-tipped, white rhizomes, which quickly spread the weed into large patches. This extensive root system makes hand-pulling ineffective, as any broken piece of rhizome can sprout a new plant.
While not a true grass, Nutsedge (often called nutgrass) is frequently mistaken for a fast-growing weed. Its key identifying feature is its triangular stem, which can be felt by rolling it between your fingers, contrasting sharply with the round stems of true grasses. Nutsedge leaves are glossy, stiff, and yellow-green. The plant often grows significantly faster than the surrounding lawn, especially in moist or poorly drained areas.
Factors Encouraging Weed Grass Growth
Improper cultural practices can inadvertently create an environment where aggressive weeds thrive over desirable turfgrass. Mowing the lawn too short severely weakens the turf and reduces its ability to compete against weeds like Crabgrass. Maintaining a taller cutting height, typically between 3 to 4 inches for cool-season grasses, encourages deeper root growth and shades the soil. This shading acts as a natural pre-emergent control, blocking the sunlight needed for weed seeds to germinate.
Watering habits also promote weed growth. Frequent, shallow watering keeps the upper few inches of soil consistently moist, encouraging the development of shallow-rooted weeds, including Nutsedge. In contrast, a deep and infrequent watering schedule forces turfgrass roots to grow deeper, making the lawn more resilient and better able to outcompete surface-level weeds. Aiming for about 1 to 1.5 inches of water per week, applied in one or two deep sessions, is recommended.
Soil compaction is another issue that favors the growth of hardy weeds. When soil particles are pressed tightly together, it reduces the pore space needed for air, water, and deep root penetration. Weeds like Crabgrass and plantain are better adapted to these poor conditions and quickly colonize thin or bare spots. Compacted soil also exacerbates drainage issues, a condition that Nutsedge particularly favors.
Strategies for Control and Removal
Active removal strategies depend on the specific weed species and its life cycle. For annual weeds like Crabgrass, the most effective long-term control is a preventative approach using a pre-emergent herbicide. This should be applied in the spring before the soil temperature reaches 55 degrees Fahrenheit. Pre-emergents work by creating a chemical barrier that inhibits the cell division of germinating seeds, killing the weed before it emerges. If Crabgrass has already emerged, a selective post-emergent herbicide containing an active ingredient like Quinclorac is necessary.
Perennial weeds that grow in clumps, such as Tall Fescue, must be removed entirely, as they will not respond to most selective lawn herbicides. Small, isolated clumps are best managed through mechanical removal, which involves digging out the entire plant and ensuring all the coarse root mass is extracted. The same mechanical effort is needed for Quackgrass. However, due to its extensive, sharp rhizome system, simply pulling the top growth causes the remaining rhizomes to sprout more vigorously. For larger Quackgrass infestations, non-selective herbicides containing glyphosate may be required as a spot treatment, though this will also kill the surrounding turf.
Nutsedge, being a sedge and not a grass, requires specialized chemical treatment since standard grassy weed herbicides are ineffective. Selective post-emergent herbicides containing active ingredients such as Halosulfuron-methyl or Sulfentrazone are designed to target sedges without harming the turfgrass. Control is most effective when applied in the early summer, before the plant develops its underground reproductive tubers, often called nutlets. Multiple applications are necessary over several weeks to fully deplete the energy reserves stored in these nutlets.