I have probably at least a ton of apple tree prunings. Everything from
twigs to several whole trees that we culled. Some are from this spring
and others from past years, probably as long ago as four years. This
year's wood is still green of course but, the three and four year old
stuff is plenty dry.
I also have at least a two lifetime supply of mulberry which I've had
good luck with just using chunks of heartwood.
Bark on or off? I've seen reports of both ways but, is there any
consensus by the experts?

Ross.