Plant kale/collard plants about a foot apart from one another. Kale has the potential to get quite large throughout the growing season.
To harvest, pick the lower leaves first and let the center continue to grow out. This allows your kale plants to continue to growing all season, providing you with kale from early spring until well after the first frosts.
Kale is very cold hardy and will tolerate significant cold. Even after quite a few hard frost, my kale is typically still doing well. Anything left at the end of the season or any over abundant harvest during the summer, I chop and freeze for smoothies, soups, quiches and hash.