I have not used the stackable corners.

The beds do need to be level or at least close to it.

If they aren't level the soil will tend to run to the low end. In effect the soil will level itself even though the frame isn't level.

If the beds are very close to level this might be tolerable for you, but if too far off the soil may actually spill out over the low end of the bed. Not immediately, but over time, particularly with rains.

Hi Victoria - welcome to raised bed gardening. It is the best way to go by far. I have 20-plus raised beds now made from various materials (emphasis on cost effectiveness). Never have tried the stackable corner joints although they seem nifty - just too expensive to be practical. I don't level my beds as my whole property is pretty flat to begin with and it has not been an issue, but if you have significant sloping you might want to consult a landscaper in your area regarding options for constructing level beds on an incline. I have seen this done and it can look beautiful, but you need carpentry skills to cut wood in a graduated way that cooperates with the slope. The finished beds should look as if they are tucked into the slope and are part of it. Hard to explain. Seriously, I would ask a landscaper.

Victoria,

Plastic will last a lot longer than wood so go for it. The vegetables don't care what is holding the soil in place whether it be stone, bricks, plastic, tree branches, tires, etc.

You'll want to terrace the area of the slope you intend on using for the bed so it is level and you won't have a problem with erosion. There is an example in a photo below of a raised bed on a slope:

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WOW! thank you for these beautiful pictures!!!What a lot of good ideas. I'm really inspired now!

Everyone is spot on. It is best to level the tops of your beds, HOWEVER you could just make the sides of your bed higher and let the soil self level. Take a 4 or 5 foot level out to your slope and see what angle your are dealing with. So say you were going to make your sides 8 inches. Make the top board 8 inches and then add to the sides and bottom/downhil side of your bed however many boards you would need to keep the soil from washing out.
It may not look pretty, but it will work until you can correct the problem.

On an incline, build the bed frames so that the downhill end is at soil level and the uphill end a little buried. Just dig a trench and set the frame in level. A little more work, but you'll be forever happier for it.

Don't use "regular" lumber, it will rot too fast. If you use pressure-treated lumber, line the inside with plastic to keep the preservatives from leaching into the soil. Better would be to use the new composite wood&plastic decking boards. It won't ever rot, but it will need some outside support every couple of feet.

I have 20 year old pressure-treated lumber framed beds and I am planning on switching to the composite stuff the end of this season.

Yardenman,
20 YEARS OLD, Man you got your money's worth out of them.

Are these going to be permanent beds? If so, I highly recommend those cement blocks you get at places like home depot for building raised beds on sloping ground. They last a very long time and look good. I know this is a picture of mostly ornamentals, but it's only a third of my terraces and the other ones contain peppers, squash, tomatoes, gourds and basil as well as flowers (I mix 'em all up). For what it's worth, we put in a new 20x2 feet bed just yesterday evening, but that one was on level ground so it was easier.
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WOW, cnetter! That's just beautiful! I'm planning to essentially rip out all the "grass" in my back yard (read "weeds" here) this winter and put in raised beds with paths between. I've got 3 raised beds thus far, with wooden sides, but you've just showed me how to make these COMPLETELY permanent, which is what I'm after because the only place I'm moving from out of this house is the churchyard. Do you have to mortar, or are these some sort of interlocking thing? (Gosh, grown-up brick Legos would be SUCH fun to play with...)

There's no need to go to the work of "ripping it out". Just cover it via lasagna gardening methods and make it all work for you with far less labor.

They're kinda sorta like legos, but they have a lip on the back instead of little bumps on top. One brand is called Windsor Stone. The real trick to making them look good is to make sure they are level. This means cutting a bit into the hill, and digging a bit of a trench if needed, but the results are worth it.
This end of the terrace, with the mini bottle gourds and squash running rampant, shows how the end gradually dissapears into the hill. The pic was taken later in the year last year:
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