While browsing, I found this beautiful cement planter fromArtsy Pretty Plants.
Its pretty easy to make, and I bet you could also finish yours in less than a day.
Watch the video tutorial below to learn the step-by-step instructions.
Image credits: Artsy Pretty Plants via Youtube
Once you get to the half-point, feather the edges and taper them.
After this, leave the balloon to allow the cement to cure for two hours.
After this, let the second half cure for an hour.
Once the cement has set, remove the balloon by popping it.
Lastly, reinforce the planter with a thin layer of cement.
Your DIY cement balloon planter is now finished!