Kale is a versatile crop that thrives in cool weather, making it a favorite for many home gardeners. Starting kale from seed is the most economical way to grow this leafy green and allows access to a greater variety of cultivars, such as ‘Red Russian’ or ‘Lacinato’. This process requires planning and careful indoor care to ensure the seedlings are robust enough for transplanting. Following a structured approach will result in a successful and long-lasting harvest.
Planning: Timing and Location Decisions
The timing of planting depends on whether you are aiming for a spring or fall harvest, as kale is a cool-season crop that turns bitter in summer heat. For a spring crop, start seeds indoors approximately four to six weeks before the last expected spring frost date. This head start ensures the plants are ready for transplanting as soon as the weather permits, allowing them to mature before summer temperatures become too high.
Direct sowing outdoors is an option, typically done in early spring once the soil is workable, or in late summer for a fall harvest. Starting seeds indoors, however, offers greater control over the environment, promoting better germination rates and protecting delicate seedlings from pests or unpredictable weather. The indoor method produces stronger, more mature plants ready to withstand the elements, which is preferred for the earliest spring crop.
The Mechanics of Indoor Seed Starting
Select a suitable container, such as multi-cell seed trays or small peat pots, ensuring they have drainage holes to prevent waterlogging. The growing medium should be a sterile seed-starting mix, which is lighter and finer than standard potting soil and helps prevent fungal diseases. Garden soil should be avoided because it can be too dense and may harbor pathogens or weed seeds.
Plant the kale seeds shallowly, covering them with about a quarter to a half-inch of the mix. Sow two to three seeds per cell to account for potential non-germination and ensure a full tray. After planting, gently water the trays from the bottom or use a fine spray to avoid disturbing the seeds, ensuring the mix is moistened but not saturated.
Kale seeds germinate best when the soil temperature is kept between 60–75°F, with an optimal temperature around 60–65°F. Covering the seed tray with a clear plastic dome helps maintain the necessary humidity and warmth for germination. Once the seeds sprout, usually within five to twelve days, the cover must be removed immediately to allow for proper air circulation and prevent damping-off disease.
Nurturing Seedlings Until Transplant
As soon as the seedlings emerge, they must be placed under a strong light source to prevent them from becoming thin and weak, a condition known as legginess. A south-facing window is often insufficient, so artificial grow lights are recommended, positioned four to six inches above the tops of the seedlings. The young plants require significant light exposure, ideally for 14 to 16 hours each day, which is easily managed using an automatic timer.
Once the seedlings develop their first set of true leaves (which appear after the initial cotyledon leaves), it is time to thin them. Thinning involves selecting the single strongest seedling in each cell and using small scissors to clip the weaker ones at the soil line, rather than pulling them out. Clipping prevents damage to the roots of the keeper plant, ensuring the remaining seedling has adequate space and resources to develop a robust stem and root system.
Watering should be consistent; the soil needs to remain moist but never waterlogged or completely dry. As the transplant date approaches, the seedlings must undergo a gradual process called hardening off, which acclimates them to the harsher outdoor environment. Begin hardening off 7 to 10 days before the final transplant date by placing the trays outside in a shaded, protected location for just one or two hours a day.
Each day, slowly increase the duration the seedlings spend outdoors, introducing them to progressively more direct sunlight, wind, and cooler temperatures. After a week to ten days, the kale plants should be able to remain outside all day and night, provided nighttime temperatures are above 45°F. This slow, deliberate exposure toughens the plant’s cell structure, preparing it for a successful transition into the garden bed.