[composting conifer needles]
This faq on composting leaves has some comments:
https://sharepoint.cahnrs.wsu.edu/bl...ng-leaves.aspx
I mix them into container mix just for the air space and drainage
that they add, without expecting them to decay to silt in a season
or two. Same thing for mulch: I will put a few inches of fir needles
on the soil and then top it off with something heavier to keep them
from blowing away in the wind. The next spring, they will still be there,
taking years to decay.