It depends on what kind of grass you have. If there is any brome grass, it will still get through. I have all kinds of raised beds, and every spring, I run along with a sprayer full of roundup and nuke a 6" strip on the outside of the raised beds.

With an added benefit that I don't have to trim the grass, just use the normal mower.

I don't mind te trimming. It's just normal Kentucky blue.

You use Roundup that close to your beds? I'm paranoid about that. I don't use any chemicals within a few feet. Is Roundup safe that close?

Bob, I have 3 acres to try and keep under control, about half that border is raised beds, so if I were to trim that by hand every few weeks, it would be a considerable amount of work. I use roundup around the flowerbeds. I just wait until a calm day and hold the nozzle about 2 inches from the ground - there isn't any drift.

Roundup only damages things that it gets on the foliage of, Bob, so, as David said, as long as you do it on a day when there's no wind you can use it right up against other things without hurting them. Roundup in the soil doesn't hurt plants--at least not the normal amount you'd use when spraying. And if you've used RU in an area you can pretty much plant new things as soon as it's dried on whatever you sprayed--tho I'm inclined to wait a day or two just to "be sure."

I don't think KBG would make it up thru 7" or more of soil, but if you happen to have any bindweed growing in your grass, that will go thru just about anything. If no bindweed or other tap-rooted things, like thistle, it seems to me you should be fine. A couple inch "buffer" like David uses seems to me it would make the lawn "upkeep" over summer a lot easier.

Skybird

Um, I am here to tell you that, yes, Kentucky Bluegrass will easily grow through 7" or more of soil. Spent the whole afternoon yesterday, digging it out of my veggie bed, and one of the perennial beds. Still have 4 more to do. I dug down a good 8" or more, and was still finding roots coming into the bed from the lawn at that depth. You could try putting a weed barrier at the bottom of the raised bed before you add the soil.

My property is completely infested with bindweed, but I spend almost just as much time eradicating the Kentucky Bluegrass out of the areas I don't want it to grow, as I do dealing with the bindweed.

Not comfortable with the Round Up near the vegetable bed, but maybe there is an organic option I haven't thought of yet.

Bonnie

Thanks everyone!

I now Roundup is a foliar thing, but plants absorb it, then die and decay. Those chemicals then get into the soil do they not?

I pride myself on having a garden with no chemicals nothing that's not natural. I don't even use fertilizer. I won't even use miracle gro.

You can get pretty much the same benefit by using a heavy mulch around the outside of the raised beds.