I tried collecting a few larches this Fall too, after seeing this thread.
I'm keeping them outside on seedling mats this winter. This will keep the roots above freezing through spring. Everything I dug up is in pure pumice.
Here's a subalpine larch:
View attachment 402235
And the root ball of a different one. I'm bare rooting several and keeping the dirt intact on several, like below. We'll see if it matters in a year or two:
View attachment 402247
And here's a tiny Western larch I dug up because of its color. The needles look healthy. Anyone seen this before? The yellow/green behind is a different tree.
View attachment 402240