Sedges are a family of tall grasses that may be cultivated in flower gardens as an ornamental plant, or "volunteer" as a weed in unexpected and undesirable locations. Easily identifiable by their obvious seed heads, triangular stems and rigid leaves, sedges can be difficult to eradicate. Most sedges propagate via underground bulbs or "nuts."
Sedge can cause problems in lawns by sowing itself among turf grasses, or in agricultural fields by presenting between row crops. In either condition, chemical-free methods are preferred over the use of herbicides. A chemical application can be used as a last resort unless sedges have appeared on organically farmed land.
Overseed alternate ground cover. According to Infonet-Biovision, clovers or other "leafy and strongly-growing legumes" can out-compete sedges. Traditionally considered a weed in lawns, clover is now being promoted as an eco-friendly lawn alternative that fixes nitrogen, grows in poor soils and is highly drought tolerant.
Hand-remove sedge if it occurs only in small amounts. Use a knife or trowel to ensure removal of the entire bulb or nut. Any missed roots will result in regermination.
"Solarise" the infested area if sedge is a widespread problem and you don't want to use chemicals. Spread plastic sheeting across the area and allow it to sit for several days in hot sun, or weeks in part shade. The heat and enclosed conditions will kill everything under the plastic, including the sedge, after which your selected turf grass can be seeded or sodded. This somewhat extreme method will result in a dead, brown lawn in need of renewal, so use this method only if you're prepared to invest the time and energy to replace the dead grasses with a strong, healthy, desirable substitute.
Use herbicides if all else fails and you are not farming or gardening organically. Ask your local garden store or nursery for a sedge-specific herbicide such as a Sulfonylurea herbicide, and apply according to package directions.
Fertilise your lawn using your usual regimen to strengthen your desired turf grasses, increasing their ability to outcompete the weakened sedges.
Mulch between rows or seed a living ground cover such as clover. Sedge grasses may continue to grow in mulch; in this case, the nut or bulb is far easier to dislodge from loose mulch than from packed earth. Living ground covers can outcompete or at least weaken sedges, allowing the desired crop to mature in a healthy manner.
Hand-weed small garden plots. Use a trowel or knife to ensure that the whole nut or bulb is removed from the earth to prevent re-emergence.
Pick a sample of your sedge, complete with seeds, and take it to your local supply store or extension office. Have a professional help you to identify the type of sedge and recommend a specifically-designed herbicide that's safe for your crops and deadly to your weeds. Apply it yourself if it's available on the market, or hire a professional outfit recommended by your local extension office if the recommended chemical is a controlled substance.
Even "safe" herbicides can carry chemicals that are detrimental to the water supply, the soil and human health. Use herbicides only as a last resort.