Hydroponic Rockwool Pack of 35 cubes with pinhole for seeds. For years, rockwool has been the go-to medium for starting seeds in hydroponics. Once seedlings are ready, they are easily transferred into whatever system you have from aeroponics to kratky, flood and drain to NFT. Rockwool cubes maintain good aeration while soaking up nutrients and do not inhibit root growth. Fits net cup sizes 2″ and larger.