Select the leaf for the birdbath. Large oak and sycamore leaves are excellent choices.
Pour the bag of sand into a pile, and cover it with plastic wrap.
Cut the stem off the leaf close to the base with scissors. Place the large leaf face down over the plastic wrap.
Mix the concrete with water using a large trowel per the directions on the package. It should look like a thick paste--not runny, but not so thick you can’t work with it.
Place the concrete on the center of the leaf, and spread it out toward the outer edges of the leaf. Cover the large veins on the leaf well with the concrete. Be careful not to tear a hole in the leaf.
Make a lip or rim for the birdbath. Cut a long strip out of cardboard about ¼ inch wide. Place it all the way around the outside edges of the leaf and blend it into the leaf with the concrete. Place plastic wrap over the leaf, and allow the concrete to harden for 48 hours.
Turn the leaf over carefully, and remove the plastic wrap by gently peeling it away from the leaf.
Paint and seal the leaf birdbath, or leave it unpainted.