Purple cabbage is a nutritious variety of the common garden vegetable, known for its vibrant color and high concentration of antioxidants called anthocyanins. This cool-season biennial is typically grown as an annual crop. It prefers temperatures that allow for slow, steady growth without the stress of intense summer heat. Cultivating this vegetable from seed to a dense, colorful head requires a methodical approach that addresses its specific needs at every stage of development.
Site Selection and Soil Preparation
Purple cabbage thrives in environments that provide consistent sun and rich, moisture-retentive soil. Select a garden area that receives at least six hours of direct sunlight each day to ensure robust head formation. Since this plant is a cool-weather crop, plan for a spring harvest by planting early or a fall harvest by planting mid-summer, aiming for maturity before high temperatures exceed 75 degrees Fahrenheit.
The soil is particularly important because cabbage is known as a heavy feeder, meaning it requires significant nutrients to form large heads. The ideal soil should be well-draining yet capable of holding moisture, high in organic matter, and have a pH level between 6.0 and 7.5. Before planting, incorporate a substantial amount of aged manure or nutrient-rich compost into the garden bed. This initial amendment provides a foundational supply of nitrogen, phosphorus, and potassium for the plant’s early development.
Planting and Spacing Requirements
You can begin your purple cabbage crop by sowing seeds indoors about four to six weeks before your region’s last expected frost date. Plant the seeds approximately one-quarter inch deep in a seed-starting mix and maintain a consistent temperature between 60 and 70 degrees Fahrenheit for optimal germination. Once the seedlings have developed their first set of true leaves, they are ready to be thinned before being moved outdoors.
Transplants should be introduced to the garden after the danger of a hard frost has passed, ideally while temperatures remain cool. Plant the seedlings slightly deeper than they were growing in their containers to provide stability and encourage strong root growth. Providing adequate space is crucial for the development of large, dense heads, so set plants 18 to 24 inches apart.
Ongoing Care and Pest Management
Consistent water is necessary for the formation of sweet, firm cabbage heads. Aim to provide one to one and a half inches of water per week, ensuring the soil remains evenly moist but not waterlogged. Applying a layer of organic mulch around the plants helps conserve this moisture, keeps the soil cool, and suppresses competing weed growth.
As the plants develop, side-dress them every two to four weeks with a nitrogen-rich liquid fertilizer, starting after the plants are well-established. Since cabbage demands a steady nutrient supply, this supplemental feeding ensures the plants have the energy needed to form a compact head. Stop nitrogen applications once the heads begin to form.
Purple cabbage, like all members of the Brassica family, is susceptible to common pests such as the imported cabbage worm and cabbage looper. These caterpillars are best managed using organic methods. Start by installing floating row covers immediately after planting to prevent the adult moths from laying eggs on the leaves. Hand-picking visible caterpillars and crushing any clusters of yellow eggs found on the undersides of leaves is an effective control measure. For heavier infestations, an application of Bacillus thuringiensis (Bt), a naturally occurring bacterium, can be sprayed onto the leaves; the caterpillars ingest it and cease feeding shortly after.
Knowing When and How to Harvest
Purple cabbage typically requires between 70 and 100 days to reach full maturity after transplanting. The primary indicator that a head is ready for harvest is its firmness and density. A mature head should feel solid and tightly packed when gently squeezed.
Harvesting should occur before a sustained period of high heat, which can cause the heads to bolt or split open. To harvest the main head, use a sharp, clean knife to cut the stem just above the lowest set of outer leaves. Leaving these wrapper leaves and the main stem in the ground can sometimes encourage the development of several smaller, secondary heads, allowing for a modest second harvest. Once harvested, the heads should be cooled and placed in refrigeration to maintain their crisp texture.