The Q&A Archives: Applying Pre-emergents

Question: I am trying to eliminate weeds from my shrub and perennial planting beds. I'm not sure when or how often I should use a pre-emergent. My lawn maintenance company did it last year in May but that did not seem to do a very good job at controlling my weeds.

What is the best time of year to apply pre-emergent weed control granuals? Should it be applied more than once (eg. early spring and summer)?

Answer: Pre-emergents must be applied before the weed seeds germinate in the spring. To stop crabgrass, for example, the material should be applied just before the forsythia blooms in the spring. There will also be a need for a later application to catch seeds that would germinate during warmer weather and at warmer soil temperatures, or if the soil surface has been disturbed. If using corn gluten, for instance, you might apply it again in about 8 weeks. For other commercial products, read and follow the label instructions carefully.

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