Potting mix really isn't the best medium for plant growing! Somehow, we've bought into the myth that a formula mixed up in a factory, using all sorts of things that plants don't normally grow in, is superior to backyard soil. People are even encouraged to use it to fill raised beds when they have poor garden soil! Consider... potting mix has no dirt! While it has no weeds, which is a minor advantage, it is sterile! Sterility may reduce disease short term, but actually makes it worse long term. Potting soil is more likely to have problems with mold, because there are no natural bacteria to inhibit mold growth. The soil is also missing the healthy probiotics which encourage plant health. It typically holds water poorly. The ingredients are often anything BUT natural, and nature simply does not formulate petroleum products as a growing medium. A mixture of dirt and compost is the best medium we have ever found for growing plants in pots, or raised beds. Compost balances out poor soil, so mixing it about half and half with poor soils will balance out most growing problems, and is more suitable for raised beds. We reluctantly use potting soil when we have no access to dirt and compost, but it really isn't a good option for keeping plants healthy and happy.