Vermiculite retains water and is best used to add retention to fast draining soil. Made from compressed mica and other silicic material, vermiculite keeps soil moist for longer periods than just regular soil. You may be wondering why not just increase the levels of coco coir or …peat moss to increase water retention? Well, by utilizing perlite instead of coco or peat, the moisture retention is better distributed as well as not as drastic as coco or peat water retention. Vermiculite works especially well in seed starting, where a small boost in moisture works wonders for seedlings. Shop now for all your vermiculite needs with HTG Supply.