 If you dig up the roots of that one, it may not come back the following year. So yes, it is wise then to leave a few roots behind so that you'll have a crop again the following year. So in the case of valerian, which by the way is a wonderful herb for helping you to go to sleep or to settle your nerves, the roots are used. You might want to grow a half a dozen or a dozen plants in a section of a garden and then