Good Morning, 

Thank you for contacting the U of M Extension Service. 

As with any chemicals you apply to the food you are growing, READ THE LABEL. 

I am not familiar with the Preen product. Here is a link to Michigan State about using Preen on a vegetable garden: https://www.canr.msu.edu/news/ask-the-expert-pre-emergent-herbicides

Applying straw or leaf mulch around your plants after they come up will help keep the weeds down. Mulch will also keep the soil cool and moist for your plants. Here is another link about mulch: https://extension.umn.edu/lawn-care/what-do-lawn-clippings

Good Luck!