Dandelions are the most common and easily identified weed in the U.S., growing anywhere there is bare soil and full sunlight. The plants'' thick, fleshy taproots can grow 2 to 3 feet deep in the soil. Yellow dandelion flowers bloom from mid-spring until frost. In warm-weather areas, they bloom all year. As the flowers mature, they form white ''puffballs'' containing seeds that the wind carries for miles to other lawns. The seeds sprout the following spring. The first fall frost kills the tops of the plants, but the taproot survives even severe winters to resprout in the spring.
To help prevent dandelions in the lawn, maintain a vigorous turf. Mow frequently enough to keep the flowers from becoming seedheads. Hand-digging dandelions is impractical, because pieces of root that are broken off and left in the soil will sprout new plants.