Most folks use 100% perlite in their hempys. Over here --->
Hempy Headquarters They are testing some super coarse perlite.
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I chase healthy roots. The roots I got in rockwool with successful germinations were bright white, fuzzy, and robust. I had more success than failure. Just a few too many failures. I may revisit rockwool when cloning time comes along, seems like it would fit into that niche very nicely.
I have experience with coco, it was available very cheap ($3 brick of Burpees) as were the fabric pots (about $5/100) . I felt comfortable making the purchase. The $25 worth of lava rock I bought a couple months ago should last me a couple of years. The nutrients are inexpensive and very effective (spent less than $25 in about a year). Most money invested here is in lights and air circulation/odor control.
In short, I am a penny pincher