Kale is a member of the Brassica oleracea species, a group of plants that thrives when temperatures drop below the average growing range for most garden vegetables. A fall harvest is highly valued because the plant’s metabolic response to cold weather improves the flavor profile of the leaves. This natural process causes the plant to convert stored starches into simple sugars, effectively sweetening the leaves and removing the bitterness often found in kale grown during the heat of summer. Therefore, securing a successful, flavorful fall crop requires precision in planting time.
Calculating the Optimal Planting Window
Determining the exact moment to plant for a fall harvest relies on a simple calculation centered around your local average first expected frost date. The goal is to ensure the kale plants reach near-full size just as the cooler weather arrives, triggering the desirable flavor transformation. Start by finding the “Days to Maturity” listed on the seed packet, which typically ranges from 50 to 75 days.
Plant growth slows down as days shorten after the summer solstice. To account for this decrease in daylight, add a buffer period of 10 to 14 days to the stated maturity time. This total duration represents the time from planting to a mature, harvest-ready plant.
Count backward from your area’s average first frost date by that total number of days to pinpoint the target week for planting your seeds. For example, a 60-day variety requires approximately 70 to 74 days of growth, meaning you must plant 10 to 11 weeks before the expected first frost. This schedule ensures the kale is large enough to withstand the first frosts and begin its sweetening process.
Choosing the Right Starting Method
Once the target planting week is established, decide between direct-sowing seeds into the garden soil or starting them indoors for later transplanting. Direct sowing is the simplest method, but the target planting window often falls in the hottest part of mid-to-late summer. Kale seeds germinate best when soil temperatures are between 60 and 70 degrees Fahrenheit, and they may fail to sprout when planted directly into soil exceeding 85 degrees.
Starting seeds indoors offers better environmental control, making it the preferred method for a reliable fall crop. Planting seeds in trays allows you to maintain the ideal germination temperature and protect sprouts from intense heat stress. Seedlings are transplanted into the garden once they have developed three to four true leaves and the extreme summer heat has slightly abated. This method allows plants to bypass the most stressful heat of the season while meeting the timeline necessary to mature before the first frost.
Mid-Season Care for Summer-Planted Kale
Growing kale during the late summer requires specific care to prevent heat stress, which can cause the leaves to become tough and bitter. Consistent watering is required; the plants need deep, regular saturation to keep the root zone cool and combat the summer heat. Applying a thick layer of organic mulch, such as straw or shredded leaves, helps to insulate the soil and maintain a cooler temperature around the roots.
To further manage heat stress, consider planting your fall kale in a location that receives full sun in the morning but is shaded from the intense afternoon sun. If a naturally shaded spot is unavailable, using a low-density shade cloth, often rated at 30 to 40 percent, can significantly reduce the temperature and prevent leaf scorch. This cooling period encourages healthy leaf development.
Late summer is also a period of heightened pest pressure for brassicas, with flea beetles and cabbage worms being the most common culprits. Flea beetles chew tiny “shotgun holes” in the leaves, while cabbage worms, the larvae of the Cabbage White butterfly, can quickly skeletonize a plant.
The most effective preventative measure is to cover the young plants immediately after transplanting with lightweight floating row covers, which physically block the adult insects from laying eggs. For actively feeding caterpillars, a biological control like Bacillus thuringiensis (Bt) is a naturally occurring soil bacterium that is sprayed onto the leaves and is safe to use on food crops.
Harvesting the Fall and Winter Crop
The successful culmination of careful timing and mid-season management is a bountiful, sweet-tasting harvest that can extend well beyond the first frost. The correct harvesting technique maximizes yield while ensuring the plant continues to produce fresh leaves. Only pick the mature, outer leaves from the bottom of the plant, using a clean cut or snap, and leave the small, central terminal bud intact.
This practice, known as cut-and-come-again harvesting, encourages the plant to continually produce new growth from the center, allowing for multiple harvests. The flavor transformation occurs when the plant detects freezing temperatures, initiating the breakdown of starches into sugars. This increased sugar content makes the leaves sweeter and adds a desirable, crisp texture. Kale is remarkably cold-tolerant and can often be harvested even after multiple hard frosts, sometimes persisting under a light layer of snow.