You can work Preen into the soil when you plant vegetable seeds, but you should not use Preen with flower seeds. Wait until the flower seedlings are two to three inches tall before spreading Preen around them.
About the Author
Melody Lee holds a degree in landscape design, is a Florida Master Gardener, and has more than 30 years of gardening experience. She currently works as a writer and copy editor. Her previous jobs include reporter, photographer and editor for a weekly newspaper.