Collard greens, a leafy vegetable popular in the United States South, are often misunderstood regarding their lifespan. They belong to the same species as cabbage and kale, Brassica oleracea, and are botanically classified as biennials. A biennial plant completes its life cycle over two years. However, collards are typically cultivated and harvested as annuals, meaning they are pulled up after the first growing season. This distinction between the plant’s natural biology and its common agricultural use explains the confusion about its true classification.
The Botanical Classification of Collards
Collards are members of the Brassicaceae family. Their life cycle is defined by how long they take to reach maturity and produce seeds. Plants fall into three primary categories: annual, biennial, and perennial. Annuals complete their life cycle within one growing season, while perennials live for more than two years.
Collard greens are biennials, meaning they focus on vegetative growth—producing the large, edible leaves—in their first year. They require a period of cold, known as vernalization, to trigger the reproductive stage. The plant then produces a flower stalk and seeds in its second year before dying.
Once the plant “bolts” or sends up a flower stalk, the leaves become tough and bitter. Therefore, growers primarily harvest collards in the first year. This practice of harvesting before the second year’s flowering cycle means they are cultivated as an annual crop. Consequently, the plant rarely completes its full two-year life cycle outside of seed production fields.
Strategies for Extending the Growing Cycle
Collards’ ability to survive winter allows gardeners in certain regions to treat them like short-lived perennials. Collard greens are cold-hardy, tolerating temperatures down to the upper teens, and often taste sweeter after a light frost. However, a hard freeze that penetrates the soil and kills the root crown will end the plant’s life.
In USDA Hardiness Zones 8 through 10, collards frequently overwinter without special protection, producing edible leaves throughout mild winter months. Gardeners in these warmer climates plant collards in the fall for a sustained harvest lasting into the following spring. Once warm weather arrives, the plants will naturally begin to bolt and produce flowers.
In colder regions, like Zones 6 and 7, gardeners use season extension techniques to protect the root system from deep-freezing. Applying a thick layer of mulch, such as straw or shredded leaves, around the base provides insulation. Using a row cover or building a cold frame creates a microclimate that shields them from the harshest temperatures.
Planting collards in a location sheltered from harsh winds, such as close to a south-facing wall, can also aid survival. The goal of these strategies is to prevent the root structure from being killed by a prolonged, deep freeze. When temperatures warm up, these protected plants often resume leaf production, extending the harvest cycle into the second year.
Harvesting Techniques for Sustained Production
To maximize the yield from a single plant over a long period, collards should be harvested using the “cut and come again” method. This technique mimics a perennial harvest, focusing on continuous production rather than a single large yield. Only the mature, outer, lower leaves should be removed from the plant.
The leaves should be harvested individually by snapping or cutting them off close to the main stem. This directs the plant’s energy toward producing new growth from the central growing point, or terminal bud. It is crucial to leave the growing crown and at least four to six young leaves intact at the top.
If the central growing point is damaged or removed, the plant will stop producing new leaves and the extended harvest will end. Consistently removing the oldest leaves from the bottom encourages the plant to grow taller, forming a long, upright stalk. This careful harvesting allows for a sustained supply of tender leaves until the plant eventually bolts in the second year.