Good question, and I'll be stnding with you in the peanut gallery, because I'm looking to fill some new raised beds as well, and can't seem to find a solid answer on what soil to mix/use.

Joe

i would increase the bark fines to 60% because the choir and peat will hold alot of water. every thing else sounds good. also if wanted to throw in another 10% of another kind of compost like steer.imo

The coir will be very high in K, and may be salty, as will the shroom compost (salty). I generally suggest that people limit the organic fraction of their RB soils to less than 20%, and that they use OM that they know will break down slowly - e.g., finished compost or pine bark. Shrinkage is going to be significant as your100% organic mix gasses out. I would also expect it to be difficult to keep a grip on the N requirements because of considerable N immobilization. Soil temps (high) may even come into play because with 100% OM, you're going to have a lot of heat generated by the composting process.

Al

terrybull and tapla ::

Thanks to both of you! I did not know coir was high in K -- the brand I use "Botanicare Cocogrow' claims to be low sodium but I have not been able to determine what the sodium level is. I will leave out the mushroom compost at this time. I will have access to bulk pine bark fines (composted and fresh) this weekend. Which would be better? Would adding perlite to the mix be OK?? In this particular RB I am only growing corn.

Thanks again,
DL

composted. you can add some perlite but its not needed in your rb.