It always helps to know the location, city/state/country to obtain accurate answers.
Have you properly identified the plant? There is a "look alike" D. scabriusculum.
http://www.mass.gov/eea/docs/d...
Are the mature plants growing on your own property? If the plants are not on your property it may be illegal in your state to collect the seeds or to dig up the plants. Please check your local laws. Here is an example from the state of Maine; scroll down to find Sowing Native Seed.
https://extension.umaine.edu/g...
The seeds need to be stratified in order to germinate. See this link:
https://plants.usda.gov/factsh...
Good luck and happy growing.
