Kales are very cold-hardy, often surviving below zero. Their flavor is best when sweetened by frost. Generally planted in mid to late summer for winter use.

Collards are actually a non-heading cabbage, with smooth leaves you can pick one by one instead of all at once in a single head. Collards tolerate heat better than any other brassica, and can be grown year-round in most climates. My mother--like many people--survived the Great Depression because collards were in the garden. 

Seed-savers should note the species in the description, as not all kales are the same.

Kale and Collards