Why can’t all weeds die with one spraying and still not hurt the grass?

This is a great question, and we wish we could offer a service like that. But unfortunately, no single chemical (or combination of chemicals) is available to control all weeds, at one time, in one spraying. There are two major weed groups that grow in your lawn throughout the year: broadleaf weeds (clover, dandelions) that grow in cool temperatures, and grassy weeds (crabgrass) that grow during warm temperatures. Each weed group has specific chemicals that are used for post-emergent control. These chemicals can only work on these weeds within a certain temperature range. For example, broadleaf weeds can be controlled if temperatures stay above 32°F. The cooler the temps the slower it takes for the results – usually 2-3 weeks. On the other hand, grassy weeds require 80°F days and 70°F nights for control. If it does not reach this range, you will not see good results.