Kale is a robust, cool-weather crop that thrives in the temperate conditions of the Pacific Northwest. Seattle’s mild, maritime climate (USDA Hardiness Zone 9a) creates an ideal environment for extended, often year-round, cultivation of this leafy green. The relatively late average first frost date in mid-November and early last frost date in late March provide a long growing season. Successful kale production relies on timing plantings to maximize the benefits of the cool spring and mild, wet autumns.
Timing the Two Main Seattle Planting Seasons
Achieving a year-round harvest requires two distinct planting periods, timed to bypass the less-than-ideal summer heat. The first planting aims for a summer harvest that begins in late spring. Start seeds indoors around late February or early March, approximately eight weeks before the last significant frost danger has passed. Transplant these seedlings in April or May, allowing them to establish a strong root system before the warmer days of July arrive.
The second planting maximizes the quality and quantity of the winter harvest, as kale flavor sweetens noticeably after exposure to frost. Schedule this planting for late summer, from late July through August. Direct-sowing or transplanting during this window ensures the plants are mature before light levels and growth rates significantly decrease after mid-October. This timing allows for continuous harvests throughout the mild Seattle winter.
Starting Kale Seeds vs. Transplants
The choice between starting kale from seed or using nursery transplants depends on the desired timing and variety selection. Starting seeds indoors six to eight weeks before planting offers the widest selection of cultivars. This method also allows for succession planting, ensuring a continuous supply of young plants. Seedlings require hardening off—a gradual process of acclimating them to outdoor conditions—before transplanting them into the garden.
Using transplants is the fastest way to get kale into the ground. This approach is particularly advantageous for the tight late-summer planting window, as it bypasses the germination and delicate seedling stages. Whether planting seeds or transplants, maintain a spacing of 12 to 18 inches between plants. Seeds should be sown about a half-inch deep, while transplants should be set at the same depth they were growing in their containers.
Essential Care for Thriving Kale
Kale requires a consistently nutrient-rich environment, performing best in fertile, well-draining soil amended with compost. While the plant prefers full sun exposure, it tolerates the partial shade common in Seattle gardens, especially during the summer. Consistent moisture is necessary for tender, flavorful leaves during dry spells, but avoid waterlogging the soil.
The mild winters in the Seattle area mean established kale plants rarely require protection from freezing temperatures. Harvest using the “cut-and-come-again” method: pick the lower, outer leaves first, leaving the central growing point intact. This technique encourages the plant to continue producing new foliage, ensuring a steady supply of greens and maintaining the plant’s vigor.