I regularly purchase potting mix in the 2 cubic foot bags, and almost
always more than I need for the current job at hand. Opened bags are
dumped into a large trash barrel with a tight fitting lid and kept in a
"bin" on my "potting bench". This is outside as I find it a much
better place for such things. Unopened bags are stacked nearby.
Freezing and thawing over the (long) winter takes care of any bugs and
most other fungi problems. However, there are beneficial fungi that
are found in certain types of soil and soil less mixes so I do not
worry too much if any do show up. I do not bake or by other means
sterilize the potting mix I use. and have not ever had any problems.

I use the same potting mix for all of my planting needs, from sowing
seeds to transplanting to potting up blooming sized perennials, as
well as all of my various types of house plants. The only thing I have
even added has been perlite to increase the drainage and aeration for
certain plants.

I've not had potting mix get "stale" per say, but I have had it get a
bit too dried out. In which case I mix it 50/50 with a new bag. If I
do not need to use it immediately, I will give the newly mixed media a
good watering, a quick "stir" with the spading fork and then leave it
alone for a few days with the lid off (unless there's rain in the
forecast!)

If by some remote chance your bag of potting mix has gotten too wet and
has soured, it can still be salvaged by opening the bag and dumping the
contents onto the ground (preferably a paved surface) letting it dry
out and then mixing in new potting mix. Cover this with a tarp and let
it "cook" for a couple of weeks and it should be ready to use - in the
garden or for potting up planters and barrels that will be used
outside. I would also NOT USE that particular brand again.

Hemmaholic

PS

Potting soil rarely stays in a bag long enough here for it to "go
stale".