I would look for a product called Rapid Rooter. Great plugs made of composted tree bark, and don't hold as much water as rockwool. If you are going to try rockwool again do NOT water them from the top. Set them on a tray and flood the tray ONLY 1/4 inch from the bottom of the rockwool. The stuff wicks water like mad so sitting in a 1/4 inch of water they will stay wet but hopefully not too wet. It will take some trial and error but give it hell you'll get it.