Hey Hippy!
I've got an old hippy recipie (for the mag part of the calmag def anyway) ... I can't confirm that it's actually a hippy recipie.
You can mix like a tablespoon of epsom salts (the kind you get for the bath in boots or walmart) in a litre of water and give it a good old spray! A tiny drop of washing up liquid will work as a surfacant (check me out ma!!) which will help the leaves absorb the goodness (basically lol...there's more science to it than that)
Spray away! .... it can't hurt! (much ... kidding. ... i don't think it can hurt)