Natural Dye expert Jenny Dean is also a genius in the garden and produces her own dye plants. Her book Wild Colour advises both on growing dye plants and using these to produce colour.
Unfortunately my garden currently ressembles a jungle but we are begining to tame it and hopefully in the future I can try dyes direct from their plant sources. Somewhere in the overgrowth I already have Rhubarb and just outside my garden Elder and Damson.
My poor neglected Rhubarb plant, lost in the wilderness!
In the meantime I get my dyestuffs online from http://www.pmwoolcraft.co.uk/