Weeds create more problems for your lawn than the obvious detraction from its appearance, according to the University of Minnesota Extension. Lawn weeds compete with grass for water and nutrients, often winning the fight and killing the desirable grasses that you want in your lawn. The first step toward solving a weed problem requires knowing the enemy you're battling by identifying the weed.
"Weed" is one of those subjective terms that depend largely on the perspective of the person using it. Lawn weeds disrupt the uniformity of the lawn, according to the Turfgrass Science series produced by Purdue and University of Illinois Extensions. By these standards, lawn grass can itself be considered a weed, if it interferes with the dominant type you're trying to establish in your yard.
Before attempting a more specific identification of your lawn weeds, determine the broad weed classification to which it belongs. This can help you to focus your efforts in the right direction. The North Carolina State University TurfFiles recognize three types of weeds: broadleaf, grass and sedge. Grasses have round or flat stems, and sedges have solid, triangular stems. All other weeds, such as dandelion and clover, count as broadleaved, characterized by wide, branching leaves.
Once you've identified the type of weed you have, the next step in obtaining a more specific identification asks you to consider the length of the plant's life cycle. Perennial weeds come back year after year for more than two years. Biennial weeds, which are often treated as perennials for control purposes, live for two years, growing the first year and producing seeds the second. Annuals live for only a year, although they may produce seed and, therefore, new annuals, every year. Annuals are further subdivided based on the season in which they germinate.
Sources of Information
Books and websites on lawn care often include pictures and detailed descriptions of lawn weeds, helping you to identify more specifically the problem you're having. Several universities maintain online identification keys, in which you select the characteristics of your weed and receive a list of possible identities. Your local extension office can help you identify weeds common in your area.
You can control weeds once you have an accurate identification. Herbicides are approved for use on different species or types of weeds and provide short-term relief of the problem. However, maintaining conditions that favor the growth of the lawn over the growth of the weed ensures that weed problems won't return and forms the most effective form of weed control, according to the University of Minnesota Extension.