Comfrey (Symphytum officinale) is a wonder plant. It is a dynamic accumulator, drawing minerals out of the soil and into the roots and leaves, a compost accelerator, a fine ingredient in liquid manure (comfrey tea), beneficial insect attractor, mulch, weed suppressant (we use it as a border around our veg plot to stop the paths getting overrun with weeds, biomass accumulator, livestock forage, human edible (comfrey fritters), a wound healer and it was traditionally called 'knit bone' by herbalists as it helps heals fractures. It's an ideal permaculture plant!
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Watch: The many uses of comfrey