This rooting medium is intended for use with the Bio Dome Seed Starter system.The Bio Planting Block will last a lifetime with these handy, economical Bio Sponges! When you're ready to begin a new crop in the Planting Block, first be sure that the block has been thoroughly disinfected (warm water with a splash of bleach is fine). Then soak the Bio Sponges you intend to use in warm water for a few minutes. They expand, revealing the pre-drilled planting hole at one end. Simply slip one seed into the hole of each Bio Sponge, place the Sponge seed-side-up in the cell of the Planting Block, and you're on your way to another bumper crop of healthy, strong, super-quick seedlings! The bio-sponges are composed of peat moss, composted fir bark, and a binding polymer. The sponges are also bio-degradable.