I have a few tips that encourage large root growth in the top third of perlite hempies. I'll try to type up the tips and method involved in-between filling up moving boxes.
It involves several up-cannings, xylem stripping, rooting hormones, node removal, root pruning and frequent misting. It'll make a 5 gallon bucket one big root mass up to two inches from the top. It's not ground breaking stuff, but it is fun to perform if you like growing roots. Back to packing ...
Peace
Keith
Cannabis plants seem to not require much in the way of encouragement to grow roots from the upper (below-ground) portions of those plants. As far as that goes, neither do the above ground portions, if they spend any real length of time in contact with a moist substrate. Makes unintentional cloning a possibility, lol - just forget to tie that drooping branch up and you're likely to find that it has grown roots. So cut it off and stick it into its own container. The more "available" oxygen, the better. So choice of media (and the ratio that it is mixed at) could play a big part, I suppose. IOW, add enough coco coir, vermiculite, et cetera to the perlite to allow it to hold a little moisture and this seems to happen more readily. IMHO.