Pre-emergent – Overapplication

Q: I have a bad feeling that putting down pre-emergent on landscape beds every six weeks is not working. Should I step it up to once a month?

A: Weed preventer products are very good at controlling weeds that come up from seeds (crabgrass, annual bluegrass, etc). But these chemicals have no effect on weeds that sprout from their own roots (wild violet, onion, bermudagrass, etc.). If applied at the recommended rate and watered-in immediately I don’t think there is a need to apply pre-emergent more often than the label instructs. Also keep in mind that over-application of a pre-emergent may harm your existing grass. Sometimes the best solution is to simply hand-pull weeds as they appear.