Knowledgebase
Crabgrass Prevention #745820
Asked April 23, 2021, 9:49 AM EDT
Anoka County Minnesota
Expert Response
It is time to apply the crabgrass preventer. Check the bag for an expiration date or phone/email the contact on the bag.
It is unlikely to be harmful but may not be full strength. Without knowing the exact contents, I can’t say for sure.
Crabgrass reproduces by seeds. The reason is that the chemicals only work to prevent crabgrass seeds from germinating. Once you see crabgrass it will have no effect on the plants that are already up. Because crabgrass needs warm soil (55 degrees for 4-5 days) to germinate, it comes up later than most grasses which gives a good window to use chemical prevention. See the following website for a more detailed explanation.
https://ag.umass.edu/sites/ag.umass.edu/files/fact-sheets/pdf/biology_mgt_crabgrass.pdf