My Dad recently got this email from Jon:

Mr. The Good,
These pics should show you all you need to know about this project. I grease all mold surfaces with motor oil. I make my concrete from 2 parts sand, one part gravel, and one part cement and water it to the consistency of peanut butter. It is important to tamp the concrete in bottom to support the inner mold. Also fill the inner mold with water so it doesn’t float. Even greased the mold will stick. Just pour boiling water on the mold sides and bottom and it will it will let go, don’t break your molds.
Sincerely,
Jon

Jon’s planters are genius. Why not make your own planters instead of buying them?