I am currently building (3) 4'x8'x22.5" based upon the plans here: http://www.ahta.org/AHTA%20Raised%20Bed.pdf for the church's community garden project. They will be finished Thursday or Friday afternoon and the 3 cubic yards of Pro-Mix and 1 ton of over-size gravel is being dropped Friday afternoon.

In talking to the "pro's" (the folks delivering the filling) they suggested that we go with the following plan:
Line with a good quality (10 year) landscape fabric
3-4" of large gravel
Fill with at least 1.5 feet of good quality top-soil

"They" said it will do a good job at keeping the Bermuda at bay for a while, but it will still make it into the beds eventually. Also, since we went with pro-mix, and it is lacking the native clay it will require more watering.

What are you going to edge the beds with? This will make a huge difference.

If you are going to use something like bricks, railroad ties, etc to edge your bed, you won't need any type of barrier along the bottom of the bed to keep the grass from growing. Lining the side of the bed with some type of barrier might not be a bad idea. Grass will not grow up through a foot of soil piled on top of it. The landscape fabric won't be necessary and could be a real problem later on. The only thing that the fabric does is eliminate the light getting to the grass. A foot of soil will do that job much better. Once weeds or grass do grow through landscaping fabric (which they seem to do with great ease), you have a huge mess on your hands.

I would also NOT use the gravel layer! I can't think of any benefit to a gravel layer, but do see some serious problems with it. The biggest problem is that it will be a barrier to proper drainage and water movement in the soil. Another issue is that it will be a partial barrier to root growth especially if you grow trees, shrubs, or plants with long taproots.

I think this is a case where simpler is much better. If you are using a border, just fill it in with soil. Ideally, I would break up the surface (just a little, a lot is not necessary) before adding soil. A shovel, mattock, or fork and just a couple of minutes should be enough. This will encourage better drainage and root growth by reducing the surface barrier at that point. If you give earthworms a decent start at breaking this barrier, they will gladly complete the task for you over a period of time.

One more thing I just thought of.....

You may want your beds a foot high for various reasons, but I would at least consider making them taller. If they were 18" - 20" tall, it would make weeding and planting a lot easier because they would be at natural sitting height.

We built some beautiful beds with loads of Wall Street Journals as the lining. The newspapers are thick and perfect but have to be covered again probably from year to year. You can see our beds were only about 8" or 10" high, and the size was 6' x 4'. They worked nicely, but had we stayed there, we were going to make them taller the next year. Sadly, after we sold our house last August, the people who bought it removed all the beds. I am attaching some pictures so you can see how we even layered newspapers all around to keep the bermuda grass at bay. On top of those we put pine straw and it worked fine and looked beautiful with the beds full and growing. I hope this helps someone.

Here is a link that might be useful: Katie's raised beds

Thank you all for all the good advices. I am thinking of using newspaper now. It seems more environment friendly than landscape fabric and cost nothing. Katiedidcottage, what do you mean by "covered again probably from year to year", did you dig out all the soil and put some newspaper in again. I hope I don't have to do that.

Thanks again!

We did spray the grass on a warm day and killed what would be under the whole area. It still tries to grow over the papers and even the pine straw and will take over if left too long without spraying the edges. You can see in the pictures that we had to spray the edges still.

I don't know about relining the beds. With the dirt being that deep, it doesn't seem like it would be necessary, but since we only used the beds for two years, I couldn't say. We layered more paper on top of the pine straw and covered it up again with more fresh pinestraw to keep the areas surrounding the beds fresh and pretty.

I got tons of Wall Street Journals from someone I knew at a law firm. They are perfect because they don't have much of the colored ink regular papers have which I didn't want to include.

Hope that helps.

The newspapers won't really hurt (assuming they are less than about 8 or 10 sheets thick), but, like Katie said, they aren't necessary with a foot of soil and probably won't serve much purpose. Although the effect would be minimal, newspaper will make the soil transition between the original soil and the new soil a little more pronounced (a slight negative). Like the landscape fabric, newspapers stop weeds by preventing light from reaching the grass/weeds. A foot of dirt will block even more light than 6 or 8 sheets of paper.

If using newspapers makes you feel better about the project, go for it, but if you are really just worried about the grass growing through, just pile on the soil.

Those raised beds are beautiful! I can't belive the next owner took them down. I have a horribly tiny yard (starter house)and the builders didn't even level all the lots. My back yard has a slight slant to the back, and then my backend neighboors slant in toward my yard so at our fence line it sometimes stays wet back there for days after rain, and the grass doesn't grow well back there I was thinking about just doing the back of the fence line a a a long raised bed but not coming out to far. Maybe just 2.5 feet or so. My husband is agaisnt it, because he said the yard is small enough as it is anyway. Plus, he is just not a big gardening fan. Maybe if I show him these pictures I can sway him

Thank you, MTLily! I wish you could have bought our house in Olive Branch! If you make the beds around your fence, 2 1/2 feet would be a good width so you could reach over to the back. Even 2 feet would be good. I've even seen some very pretty beds made from wood that had round or other shaped finials on each corner. They were gorgeous and looked very nice. They also were double height or about 18" high and really looked like a bedroom "bed" almost.

I tried to post yesterday, but it wouldn't go through that after the first year drought, I go some of the moisture crystals and sprinkled about 1/2 of a bottle in each bed which held the moisture really good so we didn't have to water every day (sometimes twice a day) like we did during the drought. If anyone does this, you might want to go lighter than I did because if it rains a lot the moisture could rot the plants.