Kale, a member of the Brassica oleracea species, can be propagated vegetatively, allowing gardeners to clone a favored plant rather than starting from seed. This process creates a genetic duplicate of the parent plant, guaranteeing the exact same leaf texture, color, and growth habit. Although kale is botanically a biennial, it is frequently grown as an annual for its leaves. Vegetative propagation is an effective way to bypass the longer seed-to-harvest cycle, extending the yield of a desirable specimen or quickly multiplying a particular variety.
Propagation Using Stem Cuttings
The most common method for cloning kale involves taking a semi-hardwood stem cutting from a healthy, non-flowering parent plant. Select a strong, side-growing stem that is approximately six to eight inches long. This stem should be taken from the lower or middle section of the plant, avoiding the tender central growth point. Use a clean, sharp blade to make a diagonal cut, ideally at a 45-degree angle, just below a leaf node.
Immediately after cutting, gently remove any leaves from the bottom half of the stem, as they would rot if buried in the rooting medium. The remaining leaves at the top should be left intact for photosynthesis, but they may be trimmed in half to reduce moisture loss. Applying a powdered rooting hormone to the cut end is recommended; this compound stimulates rapid root development and protects the cutting from fungal pathogens.
The prepared cutting is then inserted into a sterile, moist rooting medium, such as a mix of peat and perlite or a soilless potting mix. Use a medium that is consistently damp but not waterlogged, as excess moisture can cause the stem to rot before roots form. Roots typically begin to develop within two to four weeks. Providing high humidity and indirect, bright light will significantly increase the success rate.
Using Offsets and Side Shoots
A faster method of propagation utilizes the small growth points known as offsets or side shoots that emerge from the main stem of the kale plant. As the parent plant matures and lower leaves are harvested, the central stem elongates, stimulating the formation of these lateral shoots. These offsets are already partially developed and have a higher chance of immediate survival than a simple stem cutting.
To harvest an offset, carefully examine the base of the shoot where it connects to the main stem. Use a clean knife to slice the side shoot away, ensuring the cut removes a small piece of the main stem, often referred to as a “heel.” This heel tissue contains a high concentration of cells primed for root development. Unlike a stem cutting, these offsets are typically potted immediately into a nutrient-rich soil mix, requiring less time to establish roots.
Caring for the Newly Propagated Plants
Once the cuttings or offsets have developed a solid root system, they must be transitioned carefully to their permanent growing location. If the new plants rooted indoors, they must undergo a “hardening-off” period, where they are gradually exposed to outdoor conditions. This process involves placing the plants outside for increasing durations over seven to ten days, starting with an hour of shaded exposure and slowly working up to full sun. This acclimation prepares the kale for wind and direct sunlight.
Kale thrives in fertile, well-draining soil with a slightly acidic to neutral pH, ideally between 6.0 and 7.0. When transplanting, place the new kale plant at the same depth it was growing in its container, ensuring the root ball is fully covered. Consistent moisture is necessary for the first few weeks to support root establishment, typically requiring about one to one-and-a-half inches of water per week.
As kale is a leaf-producing crop, it requires high nitrogen levels to fuel foliage growth. After the initial transplanting shock has passed, usually around two weeks, introduce a balanced or high-nitrogen fertilizer. A slow-release granular fertilizer or a liquid feed applied every four to six weeks will support continuous leaf production throughout the growing season.