Collard greens (Brassica oleracea var. viridis) are a non-heading, leafy member of the cabbage family. As a cool-weather crop, collards are valued for their broad, thick, dark-green leaves and their ability to withstand temperatures that cause other greens to fail. They are typically grown as an annual, focusing the plant’s energy on producing continuous, lush foliage rather than a compact head.
Sowing the Seeds
Collards thrive in cooler conditions. For a spring harvest, begin seeds indoors four to six weeks before the last expected spring frost date, allowing seedlings to mature before warmer temperatures arrive. For the preferred fall harvest, seeds can be direct-sown in the garden during mid-summer, approximately 60 to 75 days before the first anticipated fall frost.
Collard seeds germinate best in a fertile, well-draining soil that is rich in organic matter, with a slightly acidic to neutral pH range of 6.0 to 7.0. When direct-sowing, place the seeds about one-quarter to one-half inch deep in the prepared soil. Rows should be spaced 18 to 36 inches apart, and seeds can be sown in groups of three or four every 12 to 18 inches.
Once seedlings have developed their first set of true leaves and reached a height of three to four inches, they must be thinned to their final spacing. Collard plants require considerable space, so thin the seedlings to leave the strongest plant every 12 to 18 inches. When thinning, snip the unwanted seedlings at the soil line rather than pulling them out. This avoids disturbing the roots of the remaining plants.
Ongoing Care and Environment
Providing consistent moisture ensures the leaves remain tender and flavorful. Collard greens require about one to one-and-a-half inches of water per week, delivered through deep, less frequent watering that encourages a strong root system. Watering in the morning is advisable, as it allows the foliage to dry before nightfall, helping prevent foliar diseases.
Collards are heavy feeders and particularly benefit from nitrogen-rich fertilizer, which promotes lush, dark green leaves. Gardeners should side-dress the plants every four to six weeks with an organic nitrogen source, such as composted manure or a balanced fertilizer. Apply the fertilizer a few inches away from the plant stem to prevent root burn.
While collards prefer full sun, receiving at least six hours of direct light daily, they can tolerate some partial shade, especially in hotter climates. Temperatures between 60 and 70 degrees Fahrenheit are ideal for optimal growth, but the plants are quite tolerant of cold, surviving light to medium frosts. Applying a two to three-inch layer of organic mulch, such as straw or shredded leaves, around the plants conserves soil moisture, regulates soil temperature, and suppresses weed competition.
Managing Common Pests and Diseases
Collard greens are susceptible to common Brassica pests, including the cabbage worm, flea beetle, and aphid. Cabbage worms, the larvae of the small white cabbage butterfly, chew ragged holes in the leaves. These can be managed by hand-picking the caterpillars or applying the biological control Bacillus thuringiensis (Bt). Flea beetles create numerous tiny perforations, and their damage is most severe on young seedlings, which can be protected with floating row covers.
Aphids are small, soft-bodied insects that cluster on the underside of leaves and new growth, sucking out plant sap and leaving behind a sticky residue called honeydew. Minor infestations can often be controlled by spraying the plants with a strong jet of water to dislodge the pests. For more persistent aphid problems, an application of insecticidal soap or neem oil is an effective organic solution.
Preventative measures are the most effective way to manage the few diseases that affect collards, such as clubroot or various leaf spots. These fungal issues are often soil-borne, so practicing a three-to-four-year crop rotation helps break the disease cycle. Ensuring good air circulation through proper plant spacing and avoiding overhead watering also reduces the humid conditions that favor disease growth.
Harvesting Collard Greens
Collard greens are typically ready for harvest about 60 to 80 days after planting from seed. The leaves are ready for consumption once they reach a usable size, usually around 10 to 12 inches long. Harvesting young leaves results in the best flavor, as older leaves can become tough and bitter.
The most productive way to harvest collards is by using the “cut-and-come-again” method. Only harvest the large, outer leaves from the bottom of the plant, removing them with a sharp knife or shears as close to the main stem as possible. Leave the central growing point and at least four to six inner leaves intact. This ensures the plant can continue to photosynthesize and produce new foliage.
A light frost significantly improves the flavor of collard greens by converting starches into sugars, making the leaves sweeter. Freshly harvested leaves should be washed and then wrapped in a damp paper towel. Place them in a plastic bag and refrigerate, where they will retain their quality for up to a week.