This timing is recommended when the product contains fertilizer to avoid spring fertilization. Dimension is unique from all other crabgrass control products in the fact that it can be applied after the crabgrass has germinated, as long as the plants are still small. This is the one for the procrastinators to use as it can be applied through early May with good results. The recommended time to apply most types of crabgrass control is April 1 to 15. This allows sufficient time for the herbicide to evenly spread and form an effective barrier in the soil before the seeds germinate.
Weather varies from one spring to the next and affects when it germinates.
For this reason, some people recommend to time the application of the crabgrass preventers with the blooming of the redbud trees. Weather conditions that favor full bloom of this tree also encourage the germination of crabgrass. Another way to time the application is to monitor the soil temperature. Crabgrass seed starts to germinate when the soil temperature reaches 55 degrees. Soil thermometers can be purchased at most garden centers and are very useful in timing crabgrass control and other garden plantings.