I dug up some strips of my lawn to make room for veggie beds. I've put the dug up grass into two piles. I'd love to kill the grass, cover the mounds with soil and use them for growing squash, pumpkins, beans, etc. Can anyone tell me if this grass will die if I cover it with plastic? Or will this grass keep coming back?
Unless you're a strict organic gardener you should Roundup the area you want to plant. Trouble-free compared to digging and turning over clods of soil. After the RU does it's work the soil is much easier to work with. No fuss, no muss.
But remember: grass seeds and other buried weed seeds will sprout back with a vengeance and that's where mulch takes over the job.
Believe it or not, a local nursery has an agent (manufactured in a bottle) that is a super-concentrate and selectively kills grass. It's expensive ($70) but man, does it work. It is particularly effective against that demon - Bermuda grass, my personal garden bane. One such product is Ornamec (not sure what the one I saw was). Good Luck
You should be able to find something cheaper if you look around (unless you've got a huge area of grass and need a big bottle of concentrate). The most common brand is Ortho Grass B Gon, it comes in a ready to use spray bottle for a price comparable to Roundup and things like that. They may have concentrate as well, I've never had enough grass to need a big bottle. Green Light Grass Out is another brand that I've seen around here--same deal with the ready to use spray bottle at a reasonable price.