Sustainable Practices for Vegetable Production in the South
Dr. Mary Peet, NCSU
Home

Cabbage, Broccoli, and Other Cole Crops

PRODUCTION PRACTICES: COLLARDS, KALE AND OTHER LEAFY GREENS

Turnips, mustard, collards, and kale are cool season crops and should be grown in early spring or fall for maximum yields and quality. Kale is the most cold-tolerant of the group and can withstand temperatures as low as the upper teens, while turnips, mustard and collards withstand only medium-hard frosts.

Soils and Fertilization

These leafy greens prefer well-drained soils, rich in organic matter. Loams produce the greatest yields but lighter sandy soils are preferred for overwintering and early spring crops. Fertility recommendations are given in Cole crop nutrient recommendations based on soil tests. See Soil Management for a discussion of liming materials and sources of organic nutrients. All leafy greens are subject to infection by the clubroot fungus, and should be grown at high pH (7.4) if clubroot is present in the soil.

Planting

Turnips for greens should be planted in rows 12 to 18 inches apart, spaced ¸ to 1 inch apart in the row. This will use 1¸ pounds of seed per acre. Mustard should be planted in rows 12 to 30 inches apart, 1 to 4 inches apart in the row, using 1¸ pounds seed per acre.

Three cropping systems commonly used for collards are:

  1. Set out transplants in early spring and harvest the whole plant 50 to 60 days later. Overwintered plants may bolt if they received 8 to 10 weeks of temperatures of 40 degrees F or less.
  2. Set transplants in early spring or direct seed later in spring, cut leaves in late spring and harvest the entire plant in the fall.
  3. Direct seed in mid-August and harvest the whole plant in late fall.

Direct seeding collards will require 2 pounds of seed per acre while only 4 ounces of seed are required to produce enough transplants for an acre. Spacings vary from 12 to 18 inches with 2-to-4-inch in-row spacing where young plants are to be harvested, up to rows 18 to 35 inches apart and 12-to-18 inch in-row spacing where the plants will be allowed to grow and individual leaves harvested, as in cropping system 2.

Harvesting Leafy Greens

Greens can be harvested by snapping or cutting. Turnips are harvested when tops are 4 to 8 inches high. For collards and mustard greens, either whole plants or individual leaves can be harvested. In 3 to 4 weeks, snapped plants will produce a second crop equal to 75 to 80 percent of the first harvest. Side-dressing after the first harvest increases yields of the second.

In colder weather, greens can be harvested in the afternoon, tied, washed, placed in buckets and held outdoors overnight. Otherwise, they need to be cooled to 32 degrees F with a humidity of 95 to 100 percent. Under these conditions collards can be stored for 10 to 14 days and kale and for 2 to 3 weeks.

Physiological Disorders

Tipburn causes the leaf-margins to become necrotic and is more serious on cabbage than on other crucifers. This is a calcium-related disorder but symptoms are usually not relieved by spraying with calcium. Calcium requires root pressure to move into the leaves, especially the inner leaves of the head. Where humidity or soil water is low, root pressure will also be low. Sometimes on flooded soil, root pressure can also be low because root function is impeded. Another factor that can cause tipburn is fluctuating growth rates, especially very rapid growth rates.

Reducing nitrogen rates, early harvesting and close spacing can lower tipburn damage caused by rapid growth rates.