Good idea to face the holes up. Cinder blocks that I have left outside
with the holes horizontally have generally collected paper wasp nests.
It forms a nice sheltered environment for them. The wasps don't bother
anyone unless you go to move the blocks during the summer. The wasps
disappear when the weather gets cold and don't re-use the nests next year.



madgardener wrote:
...along with interlocking blocks (gotten at box stores) you COULD use cinder
or concrete blocks, turning them upwards with the holes facing up...