i believe promix is peat, perilite, vermiculite, and dolomite lime. ive been using promix for about 8 years now i personally would not recommend growing in just peat, peat is very acidic and needs to be buffered using dolomite lime. even using pro-mix after a while all the dolomite will be used up and as the peat breaks down it will become more acidic you'll end up having to add a tbs/per 5 gallons of medium of dolomite sprinkled on top when you water to help adjust the mediums ph back up. the ideal ph for growing in peat is around 5.9-6.1. buy yourself a soil ph pen if your going to go this route anywho good luck man