It might work, but some weeds are quite resilient and might pop through. A good method I've used is to spread some newspaper over the bed first, then cover it. The paper will last long enough to smother everything, and decompose shortly after. I chop everything down with a mower or weed wackier first though, to make laying the paper easier.

Joe

If the weeds haven't gone to seed, cut them down as Joe said above. If they have gone to seed, I'd remove as many seed heads as practical to avoid them popping up a few years down the road as you work the bed. I've always used 6-10 layers of newspaper and then buried that in 4-6 inches of organics whether compost, leaves or whatever. Done in fall, the beds are ready to plant the following spring.

tj