eye will:
I'd be tempted. Is there any way to keep the growing for a longer or even continual season. i.e. let some drop their spores or replenish with more horse manure. (I understand this is a good growing medium and always wash my mushrooms very well)
The growing is EXTREMELY random - but seems to happen all at once rather than a few occasionally. Some boxes have managed 5 or 6 crops, but I have no idea if this is from the original contents or newly grown spores, but three is probably the average.
For me there is something very unappealing about growing them from manure, especially as a couple of boxes are normally kept on the top of the fridge (which is about 6 foot high).
You can also buy "plugs" which are dowels with spores that you insert into holes in damp wood left outside (such as when storms bring down tree, and they are cut into sections to be carted off - these are perfect to pick up and leave outside to provide the correct environment).