Specialty Gardening: Container Soils - Water Movement and Retention III , 1 by tapla

tapla wrote:
I'd go with something heavier than the 5:1:1 mix, so you can keep up with the water demands. Remember, the earth is going to act like a wick and remove all the perched water, so a soil as porous as the 5:1:1 mix will dry quite quickly. 50-60% topsoil, then some pine bark fines and MI peat (reed/sedge peat) should make a good soil. I helped Gymgirl figure out a raised bed soil, but I don't remember what we came up with or how she did - haven't talked to her since spring. Maybe she'll see this and add her thoughts and observations to the conversation - I'm curious myself.

This is what's in my raised beds (see picture). It's a combination of PBFs, reed/sedge peat, sand, and Turface. At first, there was a lot of shrinkage, due to the high % of OM, but as I added the used soil from my bonsai pots, a larger mineral fraction and less shrinkage was the result. If I was building a raised bed today, I think I'd use just what I suggested to you, + some Micromax or other source of insoluble micronutrients.

Al