Haven't done this yet (putting together the boxes this weekend actually) but this is what we're planning on doing for a few of our boxes where it slopes. Mel mentions putting a plywood bottom on the bottom to make the boxes portable, and drilling I think a hole every square foot? And this would basically be the same thing. Also he recommends using at least 3/4" plywood for the regular 4x4 garden.

We're just planning on putting bricks under one side to make it level. Only things I'm worried about are the weight of the mix w/ water and plants pushing the bottom out, and how long it will last before the bottom rots.

I'd also appreciate hearing from anyone who has done this.

I've done a modified version of SFG on a slope with the use of paving stones or rocks to create the sides.They don't wash away or move.I didn't do a bottom and it worked out fine.

I did level the bottom layer and dig it out a little so that it wouldn't shift.This is also the way you do stone walls.
You slant them bank into the hill so that they don't pitch forward.

Here's how I handled the slope of my yard for my boxes.

How severe is your slope? Mine is 8.3% meaning a one foot rise for a twelve foot run. There is no bottom in my boxes, I just set the open box on the dirt after digging up the sod.

Those look great. Mine is pretty severe (37%: 3ft rise over 8 ft run). That is my main problem: If I dig in, I'll be digging down about 1 1/2 ft at the top portions OR building up the same amount at the bottom. Regardless, I'll have to have dirt to fill in that amount. Obviously I'll have the dirt from digging it out if I dig down, but it will have to be amended quite a lot!

Unfortunately, I can't figure out how to get a picture in here to show the area.

I have a pretty deep bed in one spot for that reason. After digging out one side to build up the other, I had a 2.5' deep hole even though tops of the cinder blocks on the uphill edge were only an inch or two above ground level. The bottom fill on that one ended up being a couple of very old logs (mostly rotten) I had laying about; they will break down eventually, but slowly, and stay water-logged enough to not float up in a flood.

The sunniest part of my yard is steeply sloped, so I ended up building a 5x20 cinder block raised bed running east-west. My soil is clay, so I filled the bed with about 3 yds of good topsoil and then put 6 inches of Mel's Mix on top of that. First year, just starting to plant so we'll see how it turns out.

Here is a link that might be useful: Photos of garden

Finally figured this out. Here is a picture of the area I'd like to use. Pic 1: You are looking north at the bottom of my 2 story deck.

Pic 2: Looking up NE at location. Rain barrel will be located at the down spout.

Your slope is even steeper than mine and it's running East-West. Have you considered supporting the boxes on cinder blocks? That might be cheaper and easier to install than timber. If the boxes are 4x4 feet with 3/4 inch plywood bottoms you could minimize the amount of block and excavation work by supporting the boxes on the the North and South edges only. If you use standard 8x8x16 inch blocks and your slope is 37%, each support wall would need 6 blocks (3 on top, 2 mid, 1 on bottom ) ie the view looking north would be

-----------------
: SFG BOX :
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BLOCK BLOCK BLOCK
BLOCK BLOCK earth
BLOCK earth earth

Just a thought,
Mike