Crystallising edible flowers is pretty straightforward but there are a couple of tricks which make it easier. You can either use egg white or food grade Gum Arabic to adhere the sugar to the flowers. With egg white the crystallised flowers will last a couple of weeks but with Gum Arabic they will store for several weeks or in some cases months. Gum Arabic can be bought on-line or ordered in from a good chemist. A small pot is only a few pounds and lasts for ages so is worth the investment.
Dilute a couple of teaspoons of gum arabic into a flavourless alcohol such as vodka until you have a consistency slightly thinner than single cream. The gum arabic will need to be left to sit in the alcohol overnight to ensure that it properly dissolves.
White caster sugar should be used for crystallising and I find it best to put it in a hand blender to blitz for a few pulses first. Icing sugar is too fine for crystallising but the grains in caster sugar can still be a bit large for dainty flowers so a quick blitz produces something in between.
Using a fine paint brush gently paint the Gum Arabic liquid onto the edible flowers (on both sides of the petals) and then sprinkle the sugar carefully over them, (on both sides and in the cracks and crevices) so that it adheres. Knock off any surplus sugar and place on a baking sheet to dry. If you get too much sugar stuck to the petals then it can pull the flowers out of shape and flatten it so this process may take a bit of practice. Depending on the temperature in the room, the flowers may take a few hours to dry and should then be kept in an airtight container until use. The colour can also fade from the flowers if they are kept in direct sunlight.
If this seems like far too much work then there are several companies which now sell crystallised flowers on line in the UK and they are very good. We recommend http://www.meadowsweetflowers.co.uk as they are local to us and Jill is lovely.
To buy fresh flowers for crystallising yourself then do visit our shop. We have a special selection here.