I've used it on my daughter's garden in Salt Lake for a couple of years. It works both on the soil, and on top of the mulch. Being a pre-emergent herbicide, it prevents seeds from germinating, but will not kill any that have already started. You might be a wee bit late for the first application, Paul, but it sure will help as the weather warms up.
Just spent 2 weeks there, weeding until my back gave out every day . . . Phew! Now she has a huge tree in the back yard producing a billion more seeds. Preen will prevent most of those, hopefully! I can't use it in FL as most of my weeds are perennials, and it will just fertilize them . .
