So I mixed up some soil to use for summer 2014. It has all the nutrients a plant needs in it, I don't really need advice on what to put in it. Its been in big black trash bags under my deck since about April of 2014, which means its been through the heat of the summer and is going to go through this winter if I wish to use it again. My question is, is it going to be okay to use this summer or am I better off mixing up a new batch? I don't really know how long it's good for, I've never let soil sit for this long.
It's soil, it's good forever. You most likely will not have any microbial activity within the soil, so you will need to add your organic matter to get it back to life, some moisture etc and away you go. What makes you think soil would be no good ?
I'm mostly just worried about any bacteria growing in it that could be harmful. I don't wanna doom my plants before they even break the soil. I've heard of people letting their soil sit for a while but the conditions I left mine in have me a little hesitant to use it. Like I said, it's just in trash bags under my deck exposed to northeast US temperatures and possibly some moisture.
Unless you have added harmful chemicals to the soil etc then you have nothing to worry about. You can always cook it before you use it if you are that worried, but if you do you will need to add some serious organic matter to compensate for what micro organisms that are plant beneficial, you have killed in the process.