Kale is one of the ten best container vegetable plants, according to Pam Farley in Container Food Gardening: All the know-how you need to grow veggies, fruits, herbs, and other edible plants in pots.
“Kale is a versatile green, and it looks beautiful in containers even if you don’t want to eat it (I won’t tell). Look for varieties with ‘dwarf’ in the name — some types of kale grow up to 5 feet (1.5m) tall.”
Kale is a good companion plant with dill, sage, and rosemary; it doesn’t grow well with strawberries or tomatoes.
Best planted in a 3 gallon container or larger, kale prefers full sun to partial shade. Harvest begins about 45 days after germination. Remove just a few lower leaves at a time, leaving the growing point intact, and the plant will continue to produce new leaves.