I made fireweed preserves with the vast amount of plants in front and around my cabin this summer. The process is quite easy, and can sustain your jam needs through the summer, depending on how much you wildcraft. 😉
I personally only take what I need. I believe in the ethics of wildcrafting, in which you harvest one or two discovered patches and leave the rest to others to discover and forage.
You simply boil the flowers for about 2 hours, strain them and let it sit for about 5 hours once you mix in the sugar, and pectin if you like. I opt out on the pectin and add a little rhubarb to thicken it up.
I find this recipe very tasty and highly recommend it.