Weed Control Facts: Winning the Battle of the Weeds - Page 6
Depending on the brand, some of them are applied over top of the mulch, and some are applied to the soil before the mulch is applied. A pre-emergent herbicide creates a vapor barrier at the soil level that stops weed seed germination, and can be very effective at keeping your gardens weed free. They usually only last about 5 or 6 months and need to be re-applied.
Visit a full service garden center and seek the advice of a qualified professional to select the pre-emergent herbicide that will best meet your needs. Never use a pre-emergent herbicide in your vegetable garden, and be careful around areas where you intend to sow grass seed. If you spill a little in an area where you intend to plant grass, the grass will not grow. They really do work.
That's what I know about weed control. Read this article several times. Your success depends on getting the sequence of events correct.
