Harvesting Stinging nettle root

So I found a field of stinging nettle but they are pretty mature and flowering. I want to harvest the root but every time I pull up the plant, the whole things comes out of the ground so easily with the roots still in the ground. Is there a method for harvesting the roots? I want to be able to take out the whole plant so I know I am getting stinging nettle root and not the roots of another plant. Any ideas?

Use a garden fork to loosen the soil surrounding the nettles. Then you should be able to lift the whole plant out, with roots, and shake off excess soil. - Joe