Kale can be planted pretty much anywhere in the United States where there's a cool fall growing season. It's a cool-season crop, hardy to frosts and light freezes. Kale's flavor is reported to improve and sweeten with frost. Plant Kale in rows 18 inches to 2 feet apart. When the seedlings are 3 or more inches high, thin plants (see: Guide to Thinning Your Seedlings) to 10 inches apart (read about thinning) and use the thinnings for salads or as a cooked vegetable.