The Coir discs are the all natural growing medium that sit in your growing Pods. Replacements come in a pack of 5. Simply add 250ml of water, wait for the coir to expand then plant your chosen seeds. There are many other growing mediums available but we have chosen coir because it is a 100% natural by product of growing coconuts. It's eco- friendly and has a high water retention capability - perfect for growing in Pods.