I’ve purchased Miracle Gro potting soil for years to pot up my vegetable and herb seedlings. My bags last for a long time, at times, and all I do is roll the tops over to keep the bags shut so they don’t dry out. They’ve been fine. Recently we bought a bag at WalMart, I used some for a few seedlings and closed it back up with a clamp. Two weeks later I opened it up to transplant a few more and the entire top of the soil was molded over heavily. Have you ever seen that?
Well, how about purchasing your soil at Hewitt’s since this is where you go to get answers? There are two types of Miracle-Gro soils…potting soil which is sterilized and garden soil which just a bag of topsoil with a fancy name and not sterilized. The garden soil may indeed have mold spores present and could grow mold as could any bag of topsoil. Also a bag of sterile potting soil is only sterile until the bag is opened. Don’t buy a ripped or damaged bag of potting soil (especially if it is being stored outside) since it is no longer sterile. You pay more for sterile potting soil…make sure you get what you are paying for.