Gro-Blocks are similar to a plant container. Need a 3 in pot? Then choose a 3 in Gro-Block. Small plants can be fully grown in our larger Gro-Blocks. Holes are perfect size for any 1.5 in starter plug. Come in packs labeled with instructions. Big Mama is Grodan's largest block ever produced! Big enough to grow a large plant for its entire life. More than twice the amount of wool as our Hugo Block.