Dusting the root ball with a mycorrhizal inoculant when a CBD seedling goes into its final pot is cheap and the effect on root spread is visible at harvest. The fungi extend the effective root system and help with phosphorus uptake, which matters in flower. Not every product is worth buying, and the spore counts and which species actually colonise cannabis are compared on https://calmcbdseeds.com (https://calmcbdseeds.com) in a short buying guide. It does nothing in sterile hydro, so save it for soil and coco.