We’d recommend contacting the manufacturer for best advice. Looking at a label, it appears that for onions, they recommend applying Preen Garden Weed Preventer to the soil before transplanting onions. But best to double-check with them. Customer service number for Lebanon Seaboard Corporation that makes Preen is: 1-800-233-1067.
http://www.preen.com/labels/2463793.pdf
We’d recommend contacting the manufacturer for best advice. Looking at a label, it appears that for onions, they recommend applying Preen Garden Weed Preventer to the soil before transplanting onions. But best to double-check with them. Customer service number for Lebanon Seaboard Corporation that makes Preen is: 1-800-233-1067.
http://www.preen.com/labels/2463793.pdf