How to make your own seed starting medium: 1. Coco coir (damp) 2. Vermiculite 3. Worm castings (sterile)It is thought that coco coir deters gnats that can take up residence in your wet seed starting mix. Vermiculite aids in soil aeration and helps retain water. And worm castings provide a hint of nutrients for the baby seedlings without heavy fertilizers that can cause damage —Do not add fertilizer to your seed mix. I use store-bought, sterile worm castings so I’m not introducing unwanted bacter