Dandelions are nature's calcium pumps. They shoot a tap root that can push down 30 some feet (it's super thin/tiny at that point) to find that mineral and bring it up to the surface. Some thistle varieties do the same, and they bring up other essential minerals too. Oddly enough, once they have brought up enough of whatever mineral they are looking for, they die out over time. In my gardens they tend to en up getting eaten though. haha Dandelion greens are tasty when young, and thistle root is like carrot. The thistle flowers make fantastic tea if you steep the buds before they open, or cut the green bottoms off once they bloom.