Grodan A-Ok Rockwool 1.5" Starter Plugs - 12 Pack Twelve (12) 1.5" Grodan A-Ok Rockwool Starter Plugs. Grodan Rockwool Starter Plugs provide the perfect rooting media for seedlings and cuttings. A-Ok starter plugs are used prior to plugging into the larger Grodan Gro-Blocks.