I've tried to root all sorts of flower cuttings in water over the years and most seem to work, I then add compost to the water for about two weeks and then transfer to a pot and let the 'mud' dry out until just damp. I thought it was only Pelargoniums that should not be covered? I've not had major probs with propagating geraniums covered in plastic bags. If I do get mould, it's usualy because the compost is too wet.