Collard Greens

Collards are biennial, cool-weather edible garden plants in the mustard family. Plants can grow 2 to 6 feet (61 to 183 cm) tall, depending on the variety, and the Portuguese types are the tallest. They do best in full sun. The leaves are edible raw or cooked, and cooking can help tenderize tough leaves.

Sow collards in spring or fall, either by sowing seed straight into the garden or by planting purchased seedlings. Plant seed in moist soil about ¼ to ½ inch (0.6 to 1.3 cm) deep, and keep the soil moist while seedlings get established. Seeds germinate slowly in cool spring soil, so transplants are the preferred start for a spring crop; start seeds indoors six to eight weeks before the planting date. Direct seeding works well for a late-summer sowing for a fall harvest, because the soil is warmer then. For early crops started in trays, keep the soil above 75 °F (24 °C) until the seeds germinate, then lower the air temperature to about 60 °F (16 °C). Plant rows 18 to 36 inches (46 to 91 cm) apart, space plants 6 to 18 inches (15 to 46 cm) apart in the row, and thin to that spacing when seedlings reach the three-leaf stage.

Collards need plenty of nitrogen for good leaves, so test your soil before planting and fertilize according to the results. Aim for a soil pH between 6.0 and 6.5. Side-dress with nitrogen three to four weeks after planting, placing the fertilizer 4 to 6 inches (10 to 15 cm) from the plants to avoid burning the roots, then repeat three to four weeks later.

Watering. Water so the soil is moistened to at least 6 inches (15 cm) deep, and water early in the day so the leaves dry before night. Mulch helps conserve water and reduce weeds.

The main insect pests are caterpillars such as the imported cabbageworm, cabbage looper and diamondback moth caterpillar, plus harlequin bugs; aphids can appear, most often in fall. Nematodes are a big problem in sandy soils. Diseases include black rot, downy mildew and Alternaria leaf spot, and also leaf spot and bacterial leaf blight.

Collards are usually ready 60 to 80 days after direct seeding, depending on the cultivar. Pick leaves before they reach full size for the best texture. Start at the bottom of the plant and take only a few leaves from each plant so it can recover, or cut the whole plant when it is half or fully grown. Flavor is often best after a frost. Choose a slow-bolting variety to extend the season, because the flavor declines once flowers form.

Store collard leaves in a plastic bag in the refrigerator for up to 2 weeks.

Collards are listed as a problem for horses, with no detail on which part or how much is a concern.