What you need
Take your sand and cement mix and stir it up in the pot. The ratio used in this example was 1 part cement to 2 parts sand as planters need plenty of strength to avoid crumbling.
Mix the sand and cement until the have formed a thick paste.
Pour the mix into one of your containers. I have used a granola pot which is perfect. Remember down fill it to the top as when you place the second container inside it will displace the mix a little.
Add in your second containers. I have simply used a small paper coffee cup. Push this down but not quite to the bottom as the base needs to be completely solid. Make sure the coffee cup stays down by adding a stone.
Let the containers dry, this can take a couple of days so be patient! If you go at them to soon they may crumble, I waited a week to be sure and the next weekend I was able to take them out of the containers. The Granola container can be used again and again as it releases the container perfectly. The coffee cups are one use only as they tear and bend when we take out the planters.