

A general rule of thumb is aged 1 year, especially if you don’t know what they use or if they board/breed horses since there’s a lot of variability there. If the part of the pile you’re digging into had a good worm population that’s a good sign for that section, but if you get into another area and the worms vanish then don’t include that in what you take
I’ve never grown in those zones, but this page has a few tables of information that should help you out. Outside of the suggestions from A&M, figure out how many days you have til your average frost date and anything that takes fewer days to maturity is fair game