^Agreed, moisture is the enemy. During my very first grow, I bought this cheap topsoil that had just come in on the truck. It was pretty wet, but worked great. Well, three months later, I went and bought some more of that same soil, and it had sat out baking in the sun, wet, all summer long. Needless to say, that same soil damn near killed all of my plants, and was a bitch trying to figure out what the problem was. After all, it had worked great 3 months beforehand, right?lol Long story short...yes, soils can go 'sour' if left wet for long periods of time. That's basically what happens with root rot, as well.