Unwanted grass in a lawn refers to any grass species that disrupts the uniform texture, color, and density of the desired turf. This typically includes aggressive grassy weeds or undesirable perennial grasses that grow in coarse clumps. Eliminating these invaders is challenging because most traditional weed controls are designed to kill broadleaf plants, making selective removal among different grass types complicated. Successfully removing these intruders requires precise identification, targeted treatment strategies, and long-term lawn maintenance. This guide provides actionable steps for managing the common grassy weeds that compromise a healthy turf.
Identifying Common Grassy Weeds
Accurate identification is the first step, as the control method depends on the weed’s life cycle and growth habit. Crabgrass is a summer annual weed, characterized by its light green or yellowish color and a low, sprawling growth pattern radiating from a central point. It has broader leaf blades and shallow, fibrous roots, dying completely with the first hard frost and returning only by seed the following spring.
Quackgrass is a cool-season perennial that often appears blue-green and grows in upright patches, quickly becoming taller than the surrounding turf. Its underground network of sharp, white rhizomes makes it aggressive and difficult to remove mechanically. Coarse fescue or tall fescue clumps are perennial bunch-type grasses that are dark green and have a noticeably wider, rougher blade texture than finer turf species. These perennial clumps stand out because of their distinct, non-uniform growth habit and resilience to drought.
Targeted Chemical Removal Strategies
Chemical control offers an effective way to selectively manage grassy weeds, provided the product and timing are correctly matched to the target. For annual weeds like crabgrass, pre-emergent herbicides are the primary preventative measure, creating a chemical barrier in the soil that inhibits seed germination. Application timing is governed by soil temperature, ideally occurring when the soil consistently reaches 50 to 55 degrees Fahrenheit for several days. Applying the product before this threshold prevents the majority of summer annual seeds from sprouting.
If annual weeds like crabgrass have already emerged, or if perennial grassy weeds are present, post-emergent selective herbicides become necessary. Products containing active ingredients like quinclorac are specifically effective for controlling actively growing crabgrass without damaging many desirable turf species. For perennial grassy weeds such as quackgrass or tall fescue, selective control is often harder, requiring specialized products safe for only certain turf types. Herbicides containing fluazifop-P-butyl can be used to control perennial grasses in cool-season turf, while sulfosulfuron may offer a selective option for quackgrass in warm-season lawns. These systemic post-emergent treatments must be applied when the weed is actively growing so the chemical can be absorbed and transported throughout the entire plant, including the extensive root or rhizome system.
Non-Chemical and Manual Elimination
For those who prefer to avoid synthetic herbicides or for small, localized infestations, manual and non-chemical methods are available. Clumps of coarse fescue or tall fescue, which are bunch-type grasses, can be removed by digging out the entire plant. This requires removing the whole root mass to prevent re-sprouting, a task made easier after deep watering or rain. Attempting to hand-pull perennial rhizomatous grasses like quackgrass is generally unproductive and can worsen the problem, as the brittle rhizomes often break apart, leaving viable segments that quickly sprout into new plants.
For larger areas, a technique called solarization or smothering can be used to eliminate all vegetation. This non-selective method involves covering the area with clear plastic sheeting for six to eight weeks during the hottest part of summer. The plastic traps solar energy and moisture, generating soil temperatures up to 140 degrees Fahrenheit, which is lethal to existing weeds and many seeds. Highly focused, non-selective applications of horticultural vinegar or boiling water can also be used for weeds growing in cracks, sidewalks, or patio edges. Extreme care must be taken with these non-selective products, as they will kill any desirable turf they contact.
Long-Term Prevention Through Lawn Health
The primary defense against unwanted grasses is cultivating a dense, robust lawn that naturally crowds out invaders. Mowing at the highest recommended height for the turf species is an effective cultural practice for prevention. Keeping cool-season grasses like Kentucky bluegrass between 3.5 and 4 inches shades the soil surface, preventing sunlight from reaching the ground where weed seeds need it to germinate. This also encourages the desirable turf to develop a deeper, more resilient root system.
Watering practices also influence a lawn’s resistance to weeds. Deep, infrequent watering encourages grass roots to grow downward, making the turf more drought-tolerant and less reliant on surface moisture that favors shallow-rooted weeds. Proper fertilization on a consistent schedule ensures the desired turf maintains the density needed to suppress weed growth. Furthermore, addressing soil compaction through aeration allows for better water and nutrient movement, creating a favorable environment for the fine turfgrass roots.