Save your leftover henna paste in a carrot bag. You can freeze leftover henna paste for a year! When you need to do your roots, thaw some henna, section your hair, and apply the henna right down on the scalp just as if you’re piping frosting onto a cupcake, then stroke the paste down the length of your hair. This will help you get a thorough, even dye job.
Please note:If you freeze a henna/indigo mix, you'll have to add more indigo to the mix when it is thawed because freezing will spoil the indigo dye.