The question of whether kale returns each year is common for home gardeners. The answer depends significantly on the plant’s botanical nature, local climate, and specific cultivation methods. Understanding the plant’s natural life cycle and how it responds to cold temperatures determines how long it will remain productive in the garden.
Kale’s Botanical Life Cycle
Kale is generally understood to be a biennial plant, meaning its full life cycle naturally spans two growing seasons. In the first year, the plant focuses entirely on vegetative growth, developing the large, nutrient-rich leaves that gardeners harvest. This growth builds up the plant’s energy reserves for the following year.
The second year is dedicated to reproduction, triggered by cold exposure during winter months. This cold exposure, called vernalization, signals the plant to shift energy from leaf production to flowering. After surviving winter, the plant sends up a tall stalk to produce flowers and seeds, completing its biological purpose. Although kale is botanically a two-year plant, most gardeners grow it as a single-season crop, removing it after the main harvest to make way for new plantings.
Techniques for Overwintering Kale
Keeping kale alive through winter into its second year depends on local climate conditions. Mature kale plants are quite cold-hardy, with many varieties surviving temperatures down to 25 to 28 degrees Fahrenheit without damage. Some cold-tolerant varieties can even withstand sub-zero temperatures, though production slows significantly.
In regions with milder winters (USDA Hardiness Zones 7 through 10), kale may continue producing edible leaves throughout the season without significant protection. In colder climates, insulation is necessary to protect the plant’s roots and central growing point from deep freezes. Applying a thick layer of organic mulch, such as straw or shredded leaves, around the base helps insulate the soil and maintain a stable root temperature.
More extensive protection can be provided by structures like cold frames, low tunnels, or thick fabric row covers. These covers create a microclimate that shields plants from harsh winds and traps solar heat, preventing extreme temperature drops. Proper timing is also important; planting late-summer or early-fall crops allows the kale to become well-established before the coldest weather arrives, giving it the necessary vigor to endure dormancy. Successful overwintering allows the plant to resume active growth quickly once spring temperatures begin to rise.
Harvesting and Quality of Second-Year Kale
When kale survives winter and enters its second year, its focus shifts from leafy growth to seed production, known as flowering. This change is marked by the plant developing a tall, central stalk that elongates rapidly and forms flower buds. This biological shift results in a decline in leaf quality, as the plant redirects stored energy away from the foliage.
The leaves produced on second-year kale often become tougher in texture and develop a more intense, sometimes bitter flavor. This alteration is a natural consequence of the plant’s reproductive stage, though the leaves remain edible and can still be used in cooking. Gardeners wishing to prolong the leaf harvest can delay the process by cutting off the flower stalk as soon as it appears, forcing the plant to temporarily produce new leaves.
Once the main stalk begins to flower, the plant nears the end of its useful lifespan for leaf production. The small flower buds that form before opening are often called kale raab and are considered a delicacy, tasting similar to broccoli raab. After the flowers mature and the plant sets seed, it completes its two-year cycle and dies. At this point, the gardener can collect the seeds or remove the spent plant to prepare the garden for the next season.