Raised beds - really raised

I've asked a similar question back a ways but I thought I'd ask again with a twist.
The coming year we're looking at starting vegetable gardening, however the soil is all dense-pack clay. We're looking at raised beds - by which I mean building boxes and raising them about three feet off the ground because neither of us can bend over for regular weeding easily.
My back-of-the-envelope calculations show a 1m x 2.5m x .5m box, when full of wet soil, weighs in at just over 1400kg!
Has anyone here raised growing beds this high? What sizes of beds would you recommend?
Thanks!
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There were some built on the Martha Stewart show. They were shallow for things like lettuce and such which is how they kept the weight down. Here's the article:
http://www.marthastewart.com/article/salad-table
I have a friend in a wheelchair. He had raised beds built on his patio so his chair would easily roll around the concrete between beds. These beds were about counter top height. However they were soil from ground up - just really tall raised beds. Again, you don't have the weight problem because there aren't legs holding anything this way...just lots of soil to fill something this big. His beds weren't huge - 4 feet square? He had to be able to reach the center from his chair.
marcella

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My raised bed is 16' X 4' X 24". There is a 4" X 4" redwood post at each corner, and mid way on the long sides. Attached to the posts are 2" X 12" redwood planks. Never had any trouble from it. Occasionally I've had to replace a post and a couple of planks (once each), which isn't bad for 25 yr. of service.
You may want to investigate keyhole gardens. They take less space for paths and leave more space for gardens. They are particularly good for difficult to reach corners of the yard. Whether inside the garden or out, the useable portion of the garden shouldn't be more than .6m from the path. Using this reasoning, a raised rectangle with access from the perimeter, should be no more than 1.2m across. The length depends on how much garden you need.
If your garden is a meter tall, only the top .5m need be garden soil (30% - 40% sand, 30% - 40% silt, 20% - 30% sand, and 5% - 10% organic material) http://www.raw-food-health.net/RaisedVegetableGarden.html
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Billy wrote:

Here that much redwood would cost a bomb, especially 12" planks. I would use the right class of eucalyptus. Clearly price and availability will vary with your location. Ask your timber merchant for a grade that is rated durable for continuous contact with soil. Or consider concrete blocks etc instead of timber.

You may want them narrower than that if you are short of stature and/or not very flexible.

David
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As luck would have it, I'm surrounded by redwoods. The lumber isn't nearly as good as the old heart wood but it still last a fairly long time. Forever, compared to pine which rots away in a couple of years if exposed to the ground. I'm not sure what the 2 x 12s go for these days. Couple years back I bought some 4 x 4s for a project, and they were about a dollar per foot.

That's why I have colleagues to fill in what I over look ;O)

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g'day cipher,
yep as high as you want them really, 2' & 3' been done before, keep in mind you still need to reach into the bed. an consider plants that need staking like tomatos etc.,.
http://www.lensgarden.com.au/straw_bale_garden.htm
same process only you need more material to create the medium, so would suggst you have all that organised.
wrote: snipped
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Cipher wrote:

It could be more. Three feet (90cm) high obviously would be more. The higher the sides the stronger they need to be constructed and the more carefully you have to arrange drainage. The sides have to be strong enough to contain the soil but also to hold your weight as you likely to sit on the edge. For that purpose finish the top with a board that is broad enough to be comfortable. The materials will not be cheap.

I haven't built them that high but people do build them. They are built that way for the reason that you give - gardeners who cannot stoop and bend easily. I am not sure that 90cm high is necessary, probably 60cm (2ft) would do. See:
http://www.spinalistips.se/tip-raised-garden-beds-471.html
David
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I built raised beds that are 18" tall with a 6" seat around the whole edge. I can sit on the edge of the bed and reach the center from wherever I am. Beds are 4' across.
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