This year is my first with fennel and dill, but I believe snipping the flowers will indeed extend the life of the fennel. Once fennel bolts (produces flowers), that begins the process of the plant dying. We have tons of wasps and hungry anole lizards in our yard, so I always move my chrysalises into an enclosure -- even an economical pop-up laundry hamper will do (saw them on sale for $5.99 at Aldi this week).

Always a great idea to have host plants around for your butterflies, but they may not necessarily hang around after they eclose. I've released so many monarchs and black swallowtails this year, and I'm not noticing an increase in the number of these butterflies in my yard. But a least they're out there somewhere! :)

My fennels didn’t die after flowering last year. Only the parsley did. Got a couple of dozens of seedlings. I don’t know if the would grow more leaves, they probably would not spending their energy on producing seeds.

Fennel is perennial. It won't yellow and die after flowering, like dill, parsley, cilantro, ect.

Sorry if I misinformed (and perhaps this pertains only to our hot climate down here), but I was warned against allowing fennel to bolt (which can easily and prematurely happen if my plants received too much Texas sun).

You can cut it to the ground and that monster plant with a foot deep taproot will come back stronger than ever. I must have the kind that doesn't form a bulb base for cooking and it's been there 3 years. The leaves taste good though. Don't let it reseed or you'll be digging taproots next year.