Why can’t all weeds die with one spraying and still not hurt the grass?
The answer to this question is quite simply that this chemical has yet to be created. There are two major weed groups that grow in your lawn throughout the year. Broadleaf weeds (onions, clover, henbit, dandelions…) that grow in cool temperatures. And also grassy weeds (crabgrass & dallisgrass) 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 as long as temperatures stay above 32F. The cooler the temps the slower it takes for the results – usually 2-3 weeks. On the other hand, grassy weeds require 80F days and 70F nights for control. If it does not reach this range, you will not see any results.
