Kale – Growing Guide

Overview

• Name: Kale
• Botanical Name: Brassica oleracea var. acephala
• Plant Family: Brassicaceae (Mustard Family)
• Native to: Europe, with a long history of cultivation across various climates and regions.

Description

Kale is a hardy, leafy green vegetable that belongs to the Brassicaceae family, which also includes cabbage, broccoli, and cauliflower. Like collards, kale is a type of non-heading cabbage, meaning it doesn’t form a central head like traditional cabbages. While typically grown as an annual for its nutritious leaves, kale is naturally a biennial plant. In its first year, it produces a rosette of leaves around a central stem. If left to grow into its second year, kale will flower and produce seeds.

Kale’s growth habit is generally upright, with a central stem that can vary widely in height. For most common garden varieties, kale typically grows to a height of 30 to 45 cm (12 to 18 inches). However, certain varieties, such as ‘Lacinato’ (also known as dinosaur kale) or ‘Red Russian’ kale, can grow taller, reaching up to 60 cm (24 inches) or more. In optimal conditions, especially when left to grow for an extended period or if allowed to overwinter, some varieties may even reach up to 90 cm (36 inches) in height, particularly if they begin to bolt or flower in their second year.

The leaves are its most distinctive feature, varying widely in shape, size, and color. They can be flat or curly, and their colors range from deep green to bluish-green, and even purple in some varieties. The texture of the leaves can also differ, from smooth to heavily crinkled, giving kale its characteristic appearance.

The plant’s leaves are attached to the stem via short petioles and are arranged in a spiral pattern. Each leaf has a wavy or curly edge, depending on the variety, and a thick, central midrib that runs the length of the leaf. Kale leaves are generally large, with mature leaves measuring 20 to 45 cm (8 to 18 inches) long.

In its second year, kale will bolt and produce yellow, four-petaled flowers typical of the Brassicaceae family. These flowers are followed by elongated seed pods, known as siliques, which contain small, round seeds. However, when grown as an annual, kale is typically harvested before it flowers.

Kale is renowned for its ability to withstand cold temperatures, and its leaves often become sweeter after exposure to frost. This cold-hardiness, combined with its nutritional profile, makes kale a popular choice for winter gardens and a staple in many healthy diets.

Is Ornamental Kale Edible?

Ornamental kale, known for its vibrant colors and striking foliage, is technically edible, but it is primarily grown for decorative purposes. While it shares the same species as culinary kale, ornamental varieties tend to have a tougher texture and a more bitter flavor, making them less palatable (pleasant tasting) than varieties cultivated for eating. Although you can eat ornamental kale, it is generally recommended to use it as a garnish or in cooked dishes where its strong flavor can be mellowed through cooking.

Interesting Facts

1. Kale is packed with vitamins A, K, and C, along with essential minerals like iron and calcium, making it a nutrient-dense superfood. A single serving can provide more than 100% of the daily recommended intake of vitamin K.
2. Kale has a long history of cultivation, with evidence suggesting it was grown for food as far back as the 4th century BC in the eastern Mediterranean region, where it was prized for its hardiness and nutritional value.
3. Incredibly versatile in the kitchen, kale can be used in a wide variety of dishes, from salads and soups to smoothies and baked goods. Its rise in popularity is due to its superfood status, driven by its rich nutrient profile and health benefits.
4. Kale thrives in cool weather and can continue growing even in winter conditions. It is notably more frost-tolerant than most other greens, with its flavor actually improving after exposure to light frosts, which enhances its sweetness.
5. When kale (and other cold-hardy vegetables such as Brussels sprouts) are exposed to cold temperatures, they convert stored starches into sugars, which act as a natural antifreeze, helping the plants survive in cold conditions. The increase in sugar content not only protects the plant but also enhances the flavor, making the leaves taste sweeter after frost.
6. Kale chips, made by baking or dehydrating kale leaves, have become a popular healthy snack alternative to potato chips.
7. There are ornamental varieties of kale such as ‘Redbor’ and ‘Rainbow Lacinato’ which feature striking colors and textures, making them popular in decorative garden beds and edible landscapes.

Basic Growing Information

Kale is a cool-season crop that thrives in temperatures between 4-21°C (40-70°F), with an optimal range of 15-20°C (59-68°F). It grows best when temperatures stay below 24°C (75°F). Young plants can withstand temperatures as low as -4°C (25°F) without serious damage. Kale is ideal for planting in early spring or late summer to early autumn, as it tolerates light frosts and even improves in flavor after exposure to cold. Typically grown as an annual, kale is naturally a biennial and can survive mild winters to produce seeds in its second year.

Kale prefers well-draining, fertile soil rich in organic matter, with consistent moisture to support steady growth. While it can tolerate partial shade, kale performs best in full sun, especially in cooler climates. Regular watering is essential to keep the leaves tender and flavorful, but care should be taken to avoid waterlogging, which can lead to root rot.

In warmer climates, kale can struggle with heat and may bolt if temperatures rise above 25°C (77°F). To extend the growing season in such regions, consider planting kale in the cooler months or providing some shade during the hottest part of the day.

• Sun Requirements: Full sun to partial shade
• Water Requirements: Moderate
• Soil Types and Properties: Prefers rich, well-draining soil with plenty of organic matter
• Soil pH: 6.0 – 7.5
• Pot Size for Container Growing: 33cm pot or larger. Smaller growing dwarf varieties are ideal for pots.

Planting

• Best Time to Plant:
  • Climates with freezing winters: Sow seeds indoors about 6 weeks before the last frost date or directly outdoors a few weeks before the last frost. For a fall harvest, plant about 6-8 weeks before the first frost.
  • Climates with milder winters: Plant in autumn for winter harvest.

Note: Check gardening calendars for the best planting times in your location

• Spacing: Plant seeds or transplants about 30-45 cm (12-18 inches) apart in rows spaced 45-60 cm (18-24 inches) apart.
• Seed Sowing Method: Direct sow or start indoors in seed trays.
• Seed Sowing Depth: Sow seeds 6-12 mm (¼ to ½ inch) deep. Ensure the seeds are lightly covered with soil and kept moist until germination.
• Time to Harvest: Generally 7-9 weeks when planted from seed, for most varieties. Some baby kale varieties may be ready to harvest sooner, typically within 4-5 weeks.
• Mature Height/Spread: Kale plants typically grow up to 30-45 cm (12-18 inches) tall and can spread equally wide, though some larger varieties may grow taller, reaching up to 60 cm (24 inches) in height.
• Grown From: Seeds

Kale seeds germinate best in soil temperatures between 12-24°C (55-75°F). Seedlings started indoors or in a cold frame can be transplanted outdoors once they have developed 3-4 leaves and daytime temperatures consistently reach at least 10°C (50°F).

Care and Maintenance

• Watering Tips: Water regularly to keep the soil evenly moist but not soggy, especially in hot, dry conditions. Kale prefers evenly moist soil, which helps to maintain tender leaves and prevent the plant from becoming stressed, which can lead to bolting or tougher leaves.
• Fertilization: Feed with a balanced fertilizer every 4-6 weeks or side-dress with compost or manure.
• Pruning: Harvest leaves regularly to encourage new growth.
• Support: Not required.

Growing Difficulty

• Easy to moderate, making it suitable for beginner and experienced gardeners alike.

Growing Tips

• Mulch around plants to retain moisture, suppress weeds, and keep the soil temperature stable. Organic mulches like straw, compost, or shredded leaves work well and can also contribute to the soil’s fertility as they break down.
• Kale benefits from a nitrogen-rich fertilizer early in the season to support vigorous leaf development. Compost, well-rotted manure, or a balanced organic fertilizer can provide the necessary nutrients. Be cautious not to over-fertilize, as this can lead to overly lush growth that is more susceptible to pests such as aphids.
• Provide protection from extreme cold if you’re growing kale in very cold climates. Although kale is frost-tolerant and often improves in flavor after a frost, extreme temperatures can still damage the plant. Using row covers made from lightweight fabric, such as spun-bonded polyester or polypropylene, or employing cold frames can help protect the plants during harsh winter weather.

Companion Plants

• Good companion plants include: Beets, celery, cucumbers, onions, spinach, and herbs such as dill and mint.
• Avoid planting near: Other brassicas like broccoli, cauliflower, and Brussels sprouts to prevent competition and reduce the risk of spreading pests and diseases.

Common Pests and Diseases

• Pests: Cabbage worms, aphids, and flea beetles.
  • Prevention and Control Methods: Use floating row covers or insect exclusion netting to protect plants, apply organic pesticides like neem oil or insecticidal soap as needed.
• Diseases: Downy mildew, black rot.
  • Prevention and Control Methods: Ensure proper spacing for air circulation, rotate crops, and remove any infected plants promptly.

Harvesting

• Harvest Time: Start harvesting kale when the outer leaves reach about 10–15 cm (4–6 inches) in length. For baby greens, harvest 20 to 30 days after sowing seeds. Mature leaves can be harvested 50 to 75 days after seeding, typically when they are 20–25 cm (8–10 inches) long. Leaves of an autumn crop harvested after a frost will be sweeter, as the cold weather increases the sugar content in the plant.
• Harvesting Tips: Always begin by cutting the outer leaves first, allowing the inner leaves to continue growing. This method ensures the plant remains productive throughout the season. Avoid damaging the growing tip of the plant to promote ongoing growth and leaf production.
• Storage: Kale can be stored in the refrigerator for 2-3 weeks at 0°C (32°F) with 95% relative humidity. Many gardeners leave kale in the garden throughout the winter, harvesting leaves as needed. Frost not only preserves the plant but also enhances the flavor of the leaves, making them sweeter and more enjoyable.

Propagation

• Propagated by seed. For maintaining specific kale varieties, save seeds from healthy plants after allowing them to flower in their second year.

Culinary Uses

Kale is an incredibly versatile leafy green that can be used in a variety of dishes, offering both nutrition and flavor. The tender young center leaves of kale are ideal for salads due to their mild flavor and soft texture. The larger, older leaves, which tend to be tougher, are better suited for steaming, sautéing, or cooking in the same way you would prepare cabbage. Its slightly bitter, earthy taste pairs well with a range of ingredients, making it a popular choice in many cuisines.

• Salads: Fresh kale leaves, particularly the younger and more tender ones, are a nutritious addition to salads. They can be massaged with olive oil and a pinch of salt to soften their texture, making them more palatable when eaten raw. Kale pairs well with fruits like apples or citrus, nuts, and strong cheeses in salads.
• Juicing and Smoothies: Kale is a popular ingredient in green juices and smoothies, where its robust flavor can be balanced by sweet fruits like bananas, apples, or berries. It provides a significant nutrient boost, adding vitamins A, C, and K, as well as iron and antioxidants, to your drink.
• Sautéing and Stir-Frying: Kale can be quickly sautéed or stir-fried with garlic, onions, and olive oil for a simple and nutritious side dish. The heat softens the leaves, reducing their bitterness, and makes them a great addition to a wide variety of meals.
• Soups and Stews: Kale holds up well in soups and stews, retaining its texture and adding a hearty green element. It’s commonly used in dishes like Italian ribollita, Portuguese caldo verde, and various vegetable or bean soups.
• Kale Chips: Kale chips are a popular, healthy snack, and can be both baked or dehydrated, depending on the method you choose to use. Both methods result in crispy, savory kale chips, but baking is faster, while dehydrating may preserve more of the nutrients. They provide a crunchy, savory alternative to traditional chips and can be flavored with a variety of spices or nutritional yeast.
  • Baked Kale Chips: This is the most common method, where kale leaves are tossed with oil and seasonings, then spread in a single layer on a baking sheet and baked at a low temperature (typically around 135–150°C or 275–300°F) until they become crispy.
  • Dehydrated Kale Chips: In this method, the kale leaves are placed in a food dehydrator and dried at a low temperature (around 45–55°C or 110–130°F) for several hours until they become crispy. Dehydrating preserves more nutrients and can result in a slightly different texture compared to baking.
• Pasta and Grain Dishes: Kale can be incorporated into pasta dishes, risottos, or grain bowls, adding a nutritious boost and vibrant color. It can be finely chopped and mixed into sauces, or larger leaves can be wilted and stirred into the dish just before serving.
• Casseroles and Bakes: Kale is also a great addition to casseroles, gratins, and bakes. Its sturdy leaves hold up well to longer cooking times, making it a suitable ingredient for layered dishes like lasagna or vegetable bakes.
• Fermentation: Kale can be used in fermentation processes, such as making kale sauerkraut or adding it to kimchi. Fermenting kale not only extends its shelf life but also enhances its nutritional value with probiotics.

Kale’s adaptability in the kitchen, along with its impressive nutritional profile, makes it a staple in healthy eating. Whether used raw, cooked, or baked, kale adds depth and nutrition to a wide array of dishes.

In conclusion, growing kale is rewarding due to its nutritional value and versatility in the garden and kitchen. With proper care, kale provides a continuous harvest that can extend into the cooler months, making it an excellent choice for extending the growing season.

References

• Kale | Diseases and Pests, Description, Uses, Propagation. (n.d.). https://plantvillage.psu.edu/topics/kale/infos
• Growing kale. (n.d.). Extension | West Virginia University. https://extension.wvu.edu/lawn-gardening-pests/gardening/wv-garden-guide/growing-kale-in-west-virginia
• How to grow kale and collards – MSU extension. (n.d.). MSU Extension. https://www.canr.msu.edu/resources/how_to_grow_kale_and_collards
• Utah State University. (2024, February 1). How to grow kale in your garden. USU. https://extension.usu.edu/yardandgarden/research/kale-in-the-garden
• Schalau, J. & University of Arizona Cooperative Extension. (2024). Growing kale. https://extension.arizona.edu/sites/extension.arizona.edu/files/attachment/Kale.pdf
• Kale | NC State Extension Publications. (n.d.). https://content.ces.ncsu.edu/kale
• Drost, D., & Johnson, M. (2020). How to grow kale in your garden. Utah State University Extension. https://extension.usu.edu/yardandgarden/research/kale-in-the-garden.pdf