Weeds are unwanted plants growing in unwanted places. Lawn weeds compete with turf grasses for space, sunlight and top soil. The best defence against lawn weeds is a good offence; a full, healthy turf grass is impenetrable to most invading weeds. However, weak, sparsely growing lawn areas provide ample opportunities for weeds to germinate and out-compete the indigenous, more desirable grass species.
Broadleaved weeds are easy to identify by their broad, green leaves. Dandelions, clovers and plantains are among the most common and readily identifiable broadleaved weeds in North American lawns. Broadleaved weeds typically spread by seed and form isolated clumps that must be physically pulled from the base to ensure complete removal.
Grass-like weeds look very similar to lawn grasses and in some instances may actually be a true, albeit unwanted, grass variety. Crabgrass, bentgrass and quackgrass are common grassy weeds found in home lawns. Bermuda grass is an example of a true grass species that is grown as a turf grass in some areas but is also considered a grasslike weed other areas.
Sedges are closely related and resemble species of grass or grasslike weeds. Common sedge varieties include nutsedge and green kyllinga. Sedges, on close inspection, can be identified by having triangle stems and leaves that form vertically in rows of three. Sedges thrive in over-watered lawns with poor drainage.
Moss is a opportunistic weed, found in home lawns, that thrives in sparsely growing grass in shady, moist, low fertility soils. Club moss is the most common lawn moss and is identified by a single vertical stem with green leaves at the top and brown leaves near the base. Spring is the most common time for lawn moss propagation because of the excessive soil moisture and cooler temperatures.