need outside garden box advice

Hi All,
I am thinking about a raised redwood box to plant a small garden in on the side of my house.
So far I have decided to make it redwood because 1) it takes a very long time to rot, and 2) no chemicals to screw up my organic gardening. Does this sound right?
And, I would like it twenty feet long and three feet wide. Three feet so I can reach over and weed the thing with out a lot of stretching and stooping. Does this also sound right?
Questions:
1) what goes on the bottom? Nothing so water can drain out? Do I put a floor on the underside of the box? The dirt (ha ha) it will be sitting on is "decomposed sandstone" (like decomposed granite, only way, way uglier.) There is no nutritional value in it -- everything has to be replaced, amending does not work.
2) how tall should the box be? Obviously, the taller, the less stooping but the greater expense in filling it. Root need some root to grow.
3) screws or nails? As redwood dries out, nails tend to fall out
4) what do I fill it with? Straight compost? or a mixture of both? What ratio? (The compose place sells both.)
Anything I missed?
Many thanks, -T
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Todd wrote:

Redwood sounds fine to me. Leave weep holes/spaces for drainage, for air to enter, and for expansion... I'd leave an 1/4" space between boards... when redwood gets wet it expands considerably.

I'd make it 4' wide, you can reach in from *both* sides... also 4' is a better dimension for dividing standard lumber, less waste. If you're tall make the bed 6' wide, it's not very difficult for anyone over 5' 10" to reach in 3'. And there will be many times you'll find chores easier with you up into the garden, so have a step stool handy too. I'd make your raised bed as large as you have space, if you make it small you will be sorry later.

If you can eliminate the sandstone down to soil that would be best. Some people make a bottom of stainless steel hardware cloth to keep moles out but I'd not bother.

Height depends mostly on your height, but if it's 2' tall or more you will have plenty of depth for roots. Fill is the least expensive material, don't concern yourself.

Obviously screws. Sometimes steel corner brackets are a good consideration.

A mixture of about 80% good topsoil is a good start, depends what you grow. Compost will continue to decompose so you will need to add more each year... you may decide to add more topsoil and less compost, depends what you grow and results.

An ice chest for the cold beer.
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On 04/09/2013 07:07 AM, Brooklyn1 wrote:

Thank you!
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wrote:

If you can reach from both sides, 4'.

organic material

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wrote:

Nails won't hold where temps go below freezing, nails won't hold well even in warm climes; wet soil exerts tremendous pressure. Often even screws aren't enough, galvanized steel corner braces are manditory on the outside and fish plates inside.
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