To meet CNG standards potting mix can’t contain synthetic ingredients such as chemical fertilizers or synthetic wetting agents. Commercial potting mixes frequently contain one or both of these, so it’s important to check the ingredient list carefully if you purchase potting mix. If you are able, making your own potting mix gives you more control over the ingredients. It’s easiest to purchase OMRI-listed potting mix, since obtaining ingredient lists from large companies can be tricky and sometimes fruitless. However, there are many smaller, regional companies that make perfectly great potting mix with readily available, acceptable ingredient lists. Like sourcing any input, if the potting mix you want to buy is not OMRI-listed, just make sure that you’ve checked the full ingredient list for any prohibited inputs.