The trouble with Tufas!

Hypertufa is made from three ingredients: 1) Portland cement, 2) Perlite, and 3) Peat moss. The mix cures to become a porous, lightweight rock that's great for growing plants. The recipe used for the Tufa pots shown here is as follows (by volume):
-3 parts Portland
-4 parts Perlite
-5 parts Peat moss