Garden? Give this a try! A re-Post :)
Originally posted on TBN Ranch:
Approximately a 1:4 water/cement ratio.
You may also want to put some drainage holes in the planter before it completely hardens to prevent cracking.
You may also want to apply a couple coats of cement sealer after the planter is dry. This is also nice due to the fact there is so many colored cement sealers now so your planter may be colored to want you would like.