Weeds, everyone's enemies when it comes to lawns. While most think of weeds as a certain type of plant, the definition of a weed is any plant out of place in a given environment. So as we discuss weeds here, we are going to be referring to weeds in the lawn.
Weeds can be broken down into 2 basic categories, broadleaf and grassy. Grassy weeds are less common and much tougher to control, such as crabgrass. It is possible to get other varieties in your yard too, such as johnson weeds, bermuda, and several others. Most commonly though, are broadleaf weeds, such as clover, dandelion, plantain, thistle, carpetweed, chickweed, and many many more. The best way to control these weeds is to have a healthy lawn, so proper aeration, dethatching, fertilizing, etc. will go a long way. In addition we recommend pre and post emergent weed control.
Pre-emergent weed killers are applied in early spring, usually late Feb. to early Mar. Depending on the types of weeds we are needing to control and the severity, pricing may vary. Pre-emergents work before the weeds emerge from the ground, thus PRE-EMERGENT. This is especially effective on crabgrass control, as post-emergent crabgrass control is stressful to lawns moreso.
Post-emergent weed control can be done later in the season AFTER the weeds emerge, or post emerging. There are many kinds of post-emergent weed killers but only a few have great results. Post-emergents are selective herbicides which means only certain types of plants are affected, in this case the majority of broadleaf or grassy weeds. Untrained application of any herbicide can result in a stressed lawn or poor control of weeds. Grassy weed control is much tougher on the lawn as grassy weeds closer resemble the dna of, surprisingly enough, grass.
For detailed information you can check out Scott's website.