Gro-Blocks Gro-Blocks™ are similar to a ‘plant container’. Need a 3” pot? Then choose a 3” Gro-Block. Plants can be fully grown in our Gro-Blocks, for larger plants try Hugo or Big Mama our two giant sizes. Gro-Block holes are the perfect size for any 1.5” starter plug or Macroplug. The bases of the Gro-Blocks are grooved to promote drainage and to avoid "wet feet". Gro-Blocks™ comes in strips labeled with instructions.