I am am repotting and root pruning. I am starting to accumulate a lot of old mix that still has good qualities. I am trying to get in to good habits. i would like to reuse it  by remixing it with the fresh mix. I have read the common methods for sterilizing. i am not putting it in the oven or the microwave. So that leaves me with boiling water and solarizing it. The mix is pine bark, promix and perlite. I'm leaning towards the boiling water method since it will be faster. Will this method work with this type of mix? If I go the solar route. The mix is currently in black contractor clean up bags. I do have clear plastic bags also, Can I just leave them in the black bags in the sun for 6 weeks that thats it? Six weeks was recommended for cooler weather. Is there another method? If the boiling water method is ok. Can I just dump a pot of boiling water into the bags?

I don't sterilize the mix if the plant is healthy and if its not you shouldn't reuse it. You don't want to kill the good microorganisms In your mix. It's getting up potted so refresh it and reuse it with the same tree.

I don't know about the boiling water method, but I have solarized soil outside in the sun. I put mine in shallow metal bins with glass coverings - sort of like a solar oven. All the soil has to do is reach a certain temperature. I think that is around 150*F, but don't remember for sure. I would stir it up to redistribute the heat. I only left it in there a few days and all weed seeds were destroyed. And I assume micro organisms. If I were to use plastic bags, I'd use clear ones to let the sunlight in so the contents will get even warmer, spread the contents as much as possible, and turn them over or mix at least once or twice. Solar oven makers use clear lids, not black ones, for a reason. :)

Thanks Jason, that is what I was doing, but after my scare the other day I'm nervous.

Thanks Gina, I think I read that about clear bags.

I agree with what JasonV said - if your plants are healthy, no need to pastuerize your mix. I tend to re-use a lot of mix for other purposes besides figs, and sometimes it gets too many weed seeds in it. That is when I solarize. In fact, after this thread, tomorrow I'm planning on setting up some plastic bags to clean up some mix for some container lettuce. 

Things do get warmer in clear containers than black. A few years ago I set up some closed mason jars in a homemade solar oven. Two were painted black, two were left clear. After leaving the set-up in the sun, I took the temperature of the contents. Both clear containers were significantly warmer than the jars painted black. I assume the same thing would be true with plastic bags.

It really wont do anything if you sterilize it and then use unsterilized bagged mix with it.
Something happen that you feel the need to sterilize it though ?

Yes, I was root pruning a tree and a saw a few nematodes in one spot. I threw out everything with that tree, I'm still not to sure what happened because bare rooted the tree last year and didn't see anything. So until I finish checking everything I was not going to reuse any mix without sterilizing it.

Hmm thats not good.