Dandelions and bull thistle own my backyard. It's their turf now. (I'm a game developer, not a gardener.) I've tried a couple of things to kill them. I think I've decided to go with some uprooting tool.

Anyway, there are some particularly large plants (one of each at least), like a dandelion with maybe six or seven stems that are flowering. Would it be possible to kill them by depriving them of sunlight?

Some people recommend (as a last, extreme measure) blanketing your whole backyard with some sort of plastic or something that won't let light through, to kill everything. I'm just looking to take out the worst of the bunch, maybe with something heavy and light-proof like an upside-down pot.

Will this work? Do I need to cover all the leaves of the plant for it to work? How long will I have to wait, or how will I know that it worked or didn't work?