I think survival of succulents in your city has a lot to do with the pleasant weather in summers. Most of the succulents die out in summers in hotter areas. Like in some other areas, temperatures reach as 47 - 50 degrees in summers. No matter what potting soil mix you choose, or how much you care.. They will not survive. While other succulents of hotter regions will thrive there. So other than potting mix, weather and succulent type is a big factor in the success.