Johnnys 512 Mix is a complete, compost-based growing mix for soil blocks, trays, or small containers. It is a blend of mature compost, blond sphagnum, fish meal, and Perlite. No chemical fertilizer or wetting agents are added. The peat moss used in the 512 Mix is considered essentially sterile for horticultural purposes. The compost is not sterilized. Most growers will want to use the mix moistened as it comes from the bag, preserving its organic, living character. However, growers requiring a strictly sterile mix should heat-sterilize this product before use. SEED STARTING: 1. 2. 3. 4.