The plant in question: Angelica gigas, a Korean native that behaves as a biennial or short-lived perennial in these parts. I grow it as the former, letting it sow around where wanted (and removing early on where not). Apparently I might be able to get some of the larger plants to bloom an extra year if I deadheaded them, instead of allowing them to go to seed.
A. gigas is a star of high-to-late summer, with 6-to-8-inch domed flowerheads of the darkest wine color in much of August or longer. But for me the show begins them those insane-looking buds form, always prompting garden visitors to ask “What’s that?” Indeed.
This most dramatic of angelicas wants moist soil, and is adaptable in my area to sun or shade, but seems happiest in bright shade (the old happy medium of gardening conditions).
To have a successful colony, as with any biennial, you need to be vigilant and not accidentally weed out your self-sown babies each spring. You also will need varying generations of plants: some at blooming age (one year old) and some babies (to bloom next year). So I suggest to get started you buy yourself some plants, perhaps at Annie’s Annuals or Digging Dog, and also some seed, maybe from Select Seeds or Jelitto, and start a happy if eccentric-looking family.