This is a commercial mix that we at Tropiflora have is custom made 50 yards at a time. We use this formula because #1 it works for us and #2 it is economical.
Anyone can mix their own potting media and we encourage you to do so in order to best suit your needs. However, if you wish to use our proven mix, we are more than happy to oblige!
Here is the formulation:
30% Canadian Peat
30% Green Bark
30% Hardwood Chips
10% Perlite (though this can vary with availability of materials).
It also includes 3 pounds of minor elements per yard and has a pH level of 6.0 to 6.5. This mix allows good air access to the root zone, good moisture retention without getting soggy, long pot life and good substance for holding plants upright.
Note: A one quarter cubic foot bag of soil should fill over a dozen 6 inch Azalea Pots.