Take these kale growing tips to the garden:
Sowing Kale: Sow kale seeds in the garden 5 weeks before to 2 weeks before the last expected frost in spring for a summer crop. If you are in a very cold region you can start seed indoors 5 weeks before setting plants in the garden. You can start seed in a protected seedbed or coldframe rather than indoors. For an autumn and winter crop, start seed 6-8 weeks before the first expected frost. Kale is very hardy and can tolerate temperatures as low as 14°F (-10°C) once established. Sow seeds ½” (13 mm) deep. Seedlings emerge in 5-7 days at 40-70°F (4-21°C).
Growing Kale: Thin plants in the garden 12″ (30 cm) apart in rows 12-15” (30-38 cm) apart. Grow kale in compost rich, well-drained soil, in full sun. Give kale regular water keeping the soil evenly moist. After plants have reached 6” (15 cm) tall, place straw around the stems to prevent direct contact with the soil. Avoid growing kale during the heat of summer; heat will turn the leaves bitter.
Harvesting Kale: Kale will be ready for harvest 55-75 days from direct seeding. Harvest kale during the cool time of the year–from autumn through the winter to mid-spring in most regions. Clip individual leaves when they reach about 8” (20 cm) long. Pick individual outside leaves while still young and tender. Inside leaves are generally tastier than outside leaves. Cut the whole plant before it bolts in hot weather. Store kale in the refrigerator for 1-2 weeks or blanch and freeze for up to 6 months.
Detailed tips at How to Grow Kale.