Lawn Weeds Are Often Signals If weeds are growing in your lawngrass, this may indicate a problem. In order to grow and compete with weeds, lawngrasses require light, water, nutrients, air and proper temperature. If even one of these basic needs is missing, the quality of your lawn may rapidly decline and weeds may prevail. Weeds can invade your lawn at almost any time of year. Seeds of summer weeds, including large crabgrass, goosegrass and foxtail, germinate each spring. Annual bluegrass, a winter weed visible in dormant bermudagrass and Zoysia lawns, establishes from seed in late summer, fall or early spring. Winter broadleaf weeds, such as common chickweed and henbit, may also appear. Dallisgrass, dandelion, ground ivy and wild garlic are weeds that live for more than two years. Each weed in your lawn produces many viable seeds. You help weeds out with close mowing. Extended drought and high or low temperature extremes injure lawngrasses, too. Several plants may serve as indicators to signal certain problems with your lawn. White clover may indicate the need for nitrogen fertilization. Actively growing lawngrasses usually require more nitrogen than clover. Clover is also very tolerant of wet, compacted or poorly drained soils. It may become very competitive during cool, wet weather. Algae, tiny, single-celled green plants, may form a dense green or blackish-green crust on soils in areas of the lawn with few lawngrass plants. This crust often restricts the movement of water and air into soils. Algae thrives on compacted, water-logged and fertile soils. Mosses are small plants that survive in a wide range of soil and weather conditions. Mosses produce a thick, green mass in full sun or shade on both dry and wet soils. They may grow in areas of your lawn where both light and air movement is limited. Prostrate knotweed thrives in heavily trafficked lawns, playgrounds and athletic fields. This low-growing broadleaf weed adapts well to poorly drained, compacted soils. The plant grows from a thin, long taproot. Wiry, leafy stems, which radiate from the root, produce a dull, blue-green mat well below the mower blade. The best defense against troublesome weeds is a healthy, dense and actively growing lawn. You create this type of lawn by mowing often at the right height, fertilizing and liming according to soil test results and core aerifying to reduce soil compaction. You can increase the amount of light reaching your lawn under tall, isolated trees by pruning limbs below 10 feet. Air movement across the surface of your lawn may improve by thinning, transplanting or eliminating selected plants growing nearby. Take a Just for Fun Lawn Care Quiz