I know this is an old post but my company has entered the distribution of castings and worms for green roof gardening. Our main business has been the development of commercial Extensive green roof systems. We found that LWA engineered media was lacking the attributes of mychorizzal populations to help drought hearty plants to establish after planting. You see engineered media has a small percentage of organics to control weight. Sometimes less than 8%. We added castings to boost Endo and Echtomychorizzal growth so the root systems would grow outside the potting soil used in the plugs. Great results!
We have now sourced the purest black castings for organically boosting the establishment rate of new green roof implementations.
I have been an enthusiastic gardener and began to use the castings over the winter with tremendous results indoors.
If anyone is interested, we have 2 gallon containers for $20.00. Our application rate is 1 gallon per 1000 sq ft.
I would be interested in discussing larger roof top production of vegetables with any commercially minded members.
Our source can bring in a volume of worms and these are very hardy European redworms. No need to buy out the local bait shop. These will be fresher too.
http://www.greenroofsolutions.com