Make cement cloth planters. Approximately a water/cement ratio. Add 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.
Fill the balloon with water . This image illustrates why you don't completely fill the balloon you should always leave some room in the neck of the balloon, then as the form dries the pressure has somewhere to go and your clay wont split.