There are 4 favorite seedling starter mediums our customers seem to prefer. Rapid Rooters, Rockwool, Oasis Cubes, & Jiffy Pellets. Rapid Rooters are composted tree bark & an all natural polymer; that produces a rooting hormone that makes roots form faster, more abundantly, & healthy in seedlings & cuttings. Rockwool is spun rock & is very popular for seedlings & cuttings. Oasis Cubes are a spongy all natural starter medium used for starting seedlings. Oasis Cubes break down very fast, handling them is not easy because they tend to fall apart very easily. Jiffy Pellets are an inexpensive peat moss starter medium used for starting seedlings.