Sheet mulching is my favourite way to suppress grass and weeds and start a new bed. My approach is: first, a layer of cardboard, overlapping such that there is nowhere for grass to penetrate; next a layer of well-rotted manure; then a layer of straw--NOT HAY, (you'd be amazed how many people mistakenly use hay, as opposed to straw!); finally a layer of good topsoil, or my favourite, SeaSoil. You can then plant directly into this top layer. Not only do you avoid all the work of tilling, but you promote a much healthier soil ecology, and subsequently better plants. Be careful of your topsoil sources--I have seen a lot of properties unwittingly import horsetail, morning glory, and other nasty beasts by purchasing cheap material. That will leave you longing for bermuda grass! There is a lot of info on the web about sheet mulching, or 'lasagne gardening', as it sometimes called.

A soil test is always a good idea. It will inform you of any deficient or toxic mineral levels, and if you need to adjust your soil pH. Personally, I think you will never make a better investment in your garden.

I would mention that using pressure treated lumber for a vegetable garden is not advisable. I would replace it with rough cedar, which is relatively cheap, and will last years.

Thank you, bmiceli.
I had read about lasagna gardening but didn't think I had the depth to work in. Would all the layers you recommend fit since I only have 6" to work with?

6" depth is going to be limiting. 8" is better and 10-12" is best. Otherwise I agree with the cardboard layer with a raised bed filled on top of it.

Lasagna bed building has problems but if you go that route then do not limit yourself to only 6". Mound the layers up much higher. The original book recommended mounds at least 18" tall that will eventually sink down.

If for some reason you must use only 6" then I'd suggest digging down into the soil several inches creating a sunken bed that is 6" above ground but 10-12" deep over all. But doing that is 5x the work of just using 2x12 to begin with.

Dave

Bermuda spreads by rhizomes, I've pulled up ones 3 feet long into flower beds. It's almost impossible to stop. But usually easy to pull up if you get it early.

From what I've read, Bermuda grass is the worst. Where I live it isn't usualy too bad, because it tends to die in the summer unless it is irrigated. I wouldn't till it. It sounds like anything you do to push it deeper just makes it harder to get rid of. Since it is only one bed, maybe you should just pull out all the rhizomes by hand or with the aid of a small shovel or spade. You want to clean an area larger than the box so you have a buffer zone.

Here is another idea, but it is probably too late. Consider building your box with a solid bottom of plywood. That will hopefully stop grass for many years. Just set the box right on top of the grass. Put drain holes in the side of the box near the bottom, and check them for rhizomes daily. I'm sure rhizomes will eventually creep in to the box and take root.

If you are willing to wait until next year, you can solarize a generous patch (larger than the veggie box) this year and do the box next year. The grass will still recover, of course, but it will take a while, and you can defend the dead zone between the box and the edge of the lawn.

Just my 2 cents.

--McKenzie

Agree with Buford. Bermuda and zoysia grass are similar to mints that have runner roots that spread. That is why it is hard to get rid of and contain it. But as BUFORD said, it is easy to pull them up. I would recommend to get rid of the top layer with roots AND then till or turn it over THEN carefully and patiently remove any remaining roots, as much as possible.

I am against CARDBOARD SHEETING. Though it might but block the grass from spreadin and coming up , it will also block the plants roots and drainage.