Nut grass, properly known as nut sedge, is a frustrating perennial weed that can quickly take over a lawn. It is often mistaken for common grass, but it is actually a sedge, easily identified by its triangular stem when rolled between the fingers. Because of its aggressive growth habit, it is widely considered one of the most difficult weeds to manage in turfgrass areas. Controlling an infestation requires an integrated, multi-year approach targeting both the visible plant and its underground survival structures.
Why Nut Grass is So Difficult to Eradicate
The primary reason nut sedge is challenging to eliminate lies in its complex system of underground reproductive structures called tubers, or “nutlets.” A single plant can produce several hundred tubers during the growing season, typically starting once it develops five or six leaves. These tubers are the plant’s main survival mechanism, allowing it to persist in the soil for several years and sprout new plants.
These tubers are connected by rhizomes, which are underground stems that form an extensive network beneath the soil surface. When attempting manual removal, the shoot often breaks off, leaving the tubers and rhizomes intact in the soil, which quickly sprout a new plant. Tilling or cultivating the soil can worsen the problem by chopping up the rhizomes and spreading the dormant tubers to new areas. This vast underground reservoir means that any control method must be repeated over two to three years to significantly reduce the population.
Non-Chemical Removal Strategies
For small, localized infestations, non-chemical methods offer a practical and effective solution without the use of herbicides. The most direct approach is manual removal, which must be done with extreme care to ensure the entire plant structure is extracted. You must dig deep, at least 8 to 10 inches, and wide enough to remove the tubers and rhizomes connected to the main shoot. This technique is most effective on young plants before they produce a large network of new tubers.
Another non-chemical strategy is soil solarization, which uses the sun’s heat to kill the plants and underground tubers. To implement this, cover the infested area with clear plastic sheeting during the hottest summer months. The plastic traps solar energy, raising the soil temperature high enough to destroy the plant material and many of the shallow tubers. This method requires the plastic to remain in place for four to six weeks and works best when the soil is moist to enhance heat transfer.
A related method is smothering, or occultation, which deprives the nut sedge of light. This is done by covering the area with a dark material, such as black plastic or thick cardboard, blocking all sunlight. While this kills the emerged plants, it is generally less effective than solarization at killing the deep tubers, as the soil does not get as hot. Repeated cutting or mowing the plants very low can also help exhaust the plant’s energy reserves over time, reducing its ability to regrow.
Targeted Chemical Control Options
For widespread or persistent nut sedge problems, selective herbicides are often the most effective tool to target the weed without damaging the lawn. The most common active ingredients formulated to control sedges include halosulfuron-methyl, sulfentrazone, and imazaquin. These products are selective, meaning they target the sedge while leaving most turfgrass species unharmed.
Application timing is a primary factor for success when using these herbicides. The best time to apply is in the late spring or early summer when the nut sedge is actively growing, but before it begins to produce new tubers. This is typically when the plants are small and most susceptible to the herbicide. Applying the chemical later in the season after the tubers have formed requires the herbicide to travel down, which is a slower and less effective process.
Chemical control typically requires multiple applications because the herbicides do not kill all dormant tubers in the soil. A second application is usually needed four to six weeks after the first to treat new plants that have sprouted from previously dormant nutlets. Always read the label carefully, as some products require the addition of a nonionic surfactant to help the chemical stick to the plant’s waxy leaves, improving absorption and effectiveness.
Preventing Future Infestations
Long-term management shifts the focus from eradication to creating an environment where nut sedge cannot thrive. Nut sedge often indicates poor soil drainage or excessive moisture, as it prefers wet areas. Fixing leaky irrigation systems or adjusting the watering schedule to reduce soil saturation discourages its growth. Core aeration can also help improve soil drainage and reduce compaction, making the area less hospitable to nut sedge.
Another effective cultural practice is adjusting the lawn’s mowing height. Taller turfgrass creates shade at the soil level, which inhibits the germination of nut sedge tubers and suppresses the growth of small seedlings. Maintaining the lawn at the highest recommended height for the specific turfgrass type allows the desirable grass to outcompete the weed. Also, be vigilant about checking new topsoil, plants, or sod for nut sedge tubers before introducing them to the lawn to prevent new infestations.