Kale (Brassica oleracea) is a cold-hardy member of the cabbage family, making it an excellent choice for extending the harvest season in the garden. This leafy green is highly valued for its nutritional density. Planting kale from seed is a straightforward process that rewards the gardener with a consistent supply of foliage. Success relies on understanding the specific requirements for timing, placement, and early care to ensure vigorous growth.
Preparing for Sowing: Timing and Location
Kale thrives in cooler temperatures and performs best when planted to mature before the heat of summer or after the first fall frosts. For a spring harvest, sow seeds outdoors roughly four to six weeks before the average last expected frost date in your region. The seeds can germinate in soil temperatures as low as 40°F (4°C), though an optimal soil temperature of 60–65°F will ensure quicker and more reliable emergence.
For a continuous supply, consider succession planting by sowing a new batch of seeds every few weeks until temperatures consistently exceed 75°F (24°C), which can cause the leaves to become bitter. A fall crop, which often yields sweeter leaves after a light frost, should be started about three months before the anticipated first fall frost date. Choosing the right site involves selecting an area that receives full sun, though kale tolerates partial shade, especially during warmer periods.
The soil should be fertile, well-drained, and rich in organic matter to support the plant’s rapid leaf production. Kale grows best in a slightly acidic to neutral pH range of 6.0 to 7.5. Incorporating several inches of aged compost before planting will improve soil structure and provide the necessary nutrients. Gardeners can choose to sow seeds directly into the garden bed or start them indoors for a head start, transplanting the seedlings once they have matured slightly.
The Mechanics of Planting Kale Seeds
Once the soil is prepared and the timing is correct, kale seeds should be planted at a shallow depth of approximately 1/4 to 1/2 inch below the soil surface. Planting them too deep will inhibit the seedling’s ability to push through the soil and establish itself.
When direct sowing, place the seeds about one inch apart, or sow three to four seeds in clusters every 12 to 18 inches. After covering the seeds with soil, lightly firm the surface with the back of a hoe or your hand. This ensures good seed-to-soil contact, which is necessary for the seed to absorb moisture efficiently and begin germination.
The soil must be kept consistently moist immediately after planting until the seedlings emerge, which typically takes seven to twelve days depending on the soil temperature. If starting seeds indoors, use a quality seed-starting mix and sow them at the same shallow depth.
Essential Care After Planting
A deep and infrequent watering schedule should be maintained for young kale plants, aiming for about 1 to 1.5 inches of water per week. Watering deeply encourages the development of strong, deep root systems, while avoiding overhead watering helps to mitigate the risk of fungal diseases. Mulching around the plants with a layer of organic material like straw will also help to conserve soil moisture and regulate soil temperature.
Thinning the seedlings is a mandatory step, preventing overcrowding and allowing for adequate air circulation. Once the seedlings develop two to three true leaves, they should be thinned to a final spacing of 12 to 24 inches between plants. When thinning, use small scissors to snip the weaker seedlings at the soil line rather than pulling them, which can damage the roots of the remaining plants.
Young kale seedlings are vulnerable to pests like flea beetles, which create tiny holes in the leaves. Maintaining consistent soil moisture can help deter these pests until the plants are more established. Using a floating row cover immediately after planting is an effective physical barrier against various pests, including the cabbage white butterfly, which lays eggs that hatch into leaf-eating caterpillars.