The bees and I are currently loving the zinnias that have made their home in our back yard. They are technically an annual so you replant them every year but I lucked out this time! I planted them from seed in April of last year and about half of the seeds came up. I planted a lot so it was probably a good thing in the long run. Anyway, I got lazy and the end of last summer and never pulled up the horrid looking half dead plants until about November and lo and behold they reseeded themselves! I now have a smorgasbord of different color zinnias for cutting and the bees have plenty to eat!
Point of the story: plant zinnia seeds in the spring, let them die off and look like crap for a while and they will come back even more plentiful than before!