It acts on seeds. It stops weed seeds before they sprout. Used as directed, you can use it with confidence around bedding transplants or mature plants. Preen weed preventers create an invisible weed-fighting barrier beneath the soil surface that keeps weed seeds from sprouting and forming roots.

When should you Preen?

You can start your Preen routine any time before or during the growing season. There are always new weed seeds ready to sprout. Early spring is the optimal time to apply the first round of Preen, but it's not the only time to apply the first round.

How does Preen work on weeds?

When activated by water, Preen bonds with the soil in your garden. Preen then forms an invisible protective shield. It actually prevents weed seeds from forming roots. ... Any time you begin, Preen will start to work preventing new seeds from sprouting and rooting.