Kale (Brassica oleracea var. acephala) is a cool-weather vegetable that grows up to 12 to 18 inches tall, producing a rosette of edible leaves that are often ruffled. Kale completes its life cycle in two years, making it a biennial or short-lived perennial. It is more commonly grown as an annual, though it must be allowed to grow a second year to produce seeds.
Kale can tolerate freezing temperatures as low as 20 degrees Fahrenheit, which means the plant can survive winters in U.S. Department of Agriculture plant hardiness zones 8 and above. In USDA zones 7 and below, the plant generally dies in the winter and must be replanted each year. Kale is usually grown as a spring or fall crop because it suffers when temperatures consistently rise above 80 degrees Fahrenheit. Plant kale in full sunlight for best results.
Kale prefers well-draining, loamy soil enhanced with organic materials. Oregon State University recommends keeping the soil at a pH between 5.5 and 6.5. Low pH soils may require an application of lime, while high pH soils should be amended with manganese. Water kale regularly to keep the soil consistently moist but not waterlogged or flooded. Kale is prone to pests such as caterpillars, thrips, aphids and slugs. Most kale pests can be dislodged with a direct stream of water or removed by hand.
Kale may be grown from seeds, collected in the spring of the plant's second year. Seeds take three to seven days to germinate, according to Floridata, and may be started indoors about six weeks before planting time. Though kale is often grown as a vegetable, many ornamental varieties are available that offer attractive purple, pink, white or two-toned foliage. These ornamental varieties may be used as borders, massed specimens or container plants. Though not as tasty as vegetable varieties, ornamental varieties are still edible and may be used as a showy garnish.
It takes about 30 days from planting kale until harvest time. Like other leaf greens, kale may be harvested as needed throughout the growing season or the entire plant may be harvested. The large outer leaves are best for cooking and steaming, while the tender young leaves may be eaten raw in salads. Nutrient content is highest if leaves are eaten before they begin wilting. Kale can be refrigerated and stored at 32 degrees Fahrenheit for 10 to 14 days.
- University of Florida Institute of Food and Agricultural Sciences Extension: Kale — Brassica Oleracea L. (Acephala Group)
- Missouri Botanical Garden: Brassica Oleracea (Ornamental Cabbage and Kale Group)
- Oregon State University: Collards and Kale
- U.S. Department of Agriculture: USDA Plant Hardiness Zone Map
- Floridata: Brassica Oleracea Var. Acephala
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