Its a well known fact among gardeners around here that kale/collards and other brassicas like broccoli and cauliflower don't set seed in my climate (NNSW, Australia) [borderline Sub-temperate/Sub-tropical].
Kale is still a productive crop though, so growers grudgingly buy seed again and again.
I've recently been pleased to find that 'Georgia Southern Collards' set masses of viable seed with good germination rates, in addition to their giant leaves at which people marvel.
Its also a very hardy plant in regards to our scorching heat and drought.
This may not be news to American permies, but collards are scarcely known and not commonly sold in Oz.
If your in the more tropical parts of the country and can't get your hands on a perennial kale/collard - I'd highly recommend this variety.
[Seed was sourced from eBay - cheap, but very few seeds in a packet]
Kale survives the winter and sets seed in my greenhouse, which gets down to -5C or colder for about 60 to 90 nights of winter. Or is your climate too hot for it?
Works at a residential alternative high school in the Himalayas SECMOL.org . "Back home" is Cape Cod, E Coast USA.
posted 7 months ago
Too hot here, very hot and dry after a wet autumn/winter. Avg of 1 day/year of 2C or less. No frosts here on my property, not since the late 90s.
Kales set seed just fine in the cooler, more southern parts of Australia.
My experience with various varieties of kale has been either shriveled unformed seed-pods after flowering (followed by the plant dying down) or no flowering at all resulting in opportunistic perennialism for 4 or 5 years.
[Extra hardy and productive when perennialized, but leaf quality declines with age and its roots take over a large volume of soil]
Fellow gardeners round here lament the lack of seeds on broccoli and cauliflower more-so than kale, but I'm all about those leafy greens.