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Kale is an easy-to-grow, cool-weather crop favored by gardeners everywhere. As members of the Brassicaceae family, kale and collard greens are both varieties of non-heading cabbage, and are related to broccoli, cauliflower, Brussel sprouts, kohlrabi, and bok choi, too.
Here how to grow kale organically in your garden (and why you might want to)…
- History of Growing Kale
- Varieties of Kale
- How to Grow Kale
- Special Tips for Growing Kale
- Kale Pests and Diseases
- How to Harvest and Store Kale
- How to Save Kale Seeds
- How to Use Kale
History of Growing Kale
Kale was originally selected from the European wild cabbage, and was grown as a food crop in the Mediterranean region of Europe and Asia Minor as early as 2000 BCE. Non-heading, curly-leaved and flat-leaved varieties of cabbage were described in Greece texts dating from the 4th century BCE. These forms of loose-leaf cabbage were later referred to by the Romans as Sabellian kale, from the Roman word, “caulis”, referring to this whole group of plants, and are considered to be the ancestors of modern kale plants.
Cabbage, collards, and kale were spread across Europe and Asia by the Romans, and became the most popular green vegetables in Western Europe during the Middle Ages. The Celts in particular took to these cold-loving crops and spread them across the British Isles. In fact, the scientific name for cabbages (Brassica) actually comes from the Celtic word for this plant: “bresic”.
Cabbage and kale were later brought to the New World by the colonists from England, with the first written record of them in 1669. By the 1700s, cabbage and kale were extensively grown by both colonists and native peoples.
In the nineteenth century, Russian red kale was introduced by Russian traders into Canada, and then into the United States. For most of the twentieth century, kale was used in the United States primarily for decorative purposes, but it became more popular as a vegetable in the 1990s due to its high nutritional value.
Varieties of Kale
Kales are differentiated by length of stem and leaf type. The two main types are Scotch or “curly” kale (from the Celts), which have very curled or crumpled leaves, and the Siberian or Russian types, which are flat or less curled. There are dwarf and tall selections of both.
There are many different varieties of kale you can buy to grow in your garden, including some ornamental ones, with leaf colors in blue-green, magenta, white, and purple to almost black. Popular kale varieties include:
- ‘Blue Curled Scotch‘ – the most common type of curly-leafed kale
- ‘Lacinato‘ (dinosaur kale) – a flat-leafed variety often used in Italian cooking and soups or stews
- ‘Red Russian‘ – a tender, flat-leafed, red-stemmed variety often picked young and used in salads
- ‘Redbor’ – a stunning, deep purple, curly variety that grows 3 feet tall!
- ‘Thousandhead’ – a unique kale variety with wide, flat leaves that can grow up to 3 feet long!
How to Grow Kale
Like all cabbage family members, kale is biennial, but it is typically grown as an annual. Kale grows in all climate zones, but if you live in zone 6 or warmer, you can easily overwinter your kale for an early spring crop. In the warmest climates, you can harvest kale year-round!
Just two to four plants per person are sufficient to provide plenty of leafy greens during the cool spring and fall months.
Soil Preparation for Kale
You can grow kale in traditional garden beds, raised beds, or containers. If you decide to grow your kale in pots, make sure the container is at least 10 inches deep. You can also mix colorful kale plants into your ornamental gardens. Just harvest the plants entirely before they bolt to seed or get too tall and leggy to look nice.
Kale requires slightly acidic (6.5 pH), well-draining soil that is enriched with a lot of organic compost (30 lbs per 100 square feet). For a better harvest, grow a nitrogen-fixing, legume cover crop in your garden bed and till it in before planting your kale.
Kale grows best in full sun, but it will also do well in partial shade, as long as it gets at least four hours of direct sun per day.
Kale can be sown directly into the garden or started indoors and then transplanted into the garden. You can direct seed in cold climates as soon as the soil temperature is at least 45 degrees Fahrenheit.
Start kale plants indoors in a seed-starting mix about six weeks before your last expected frost date. Plant seeds 1/4-inch deep and keep them moist. Kale seeds germinate quickly in warm soil and should sprout up within five to eight days. Transplant to the garden as soon as the soil is workable.
For fall harvest, sow seeds directly into the garden from July through September for a late fall crop that will taste super sweet after a bit of frost exposure.
Space your seedlings about 12 to 15 inches apart in rows that are 18 to 24 inches apart, allowing them the space they need to get big and lush. If you use intensive spacing (like the Square Foot method), space plants between 10 and 12 inches apart. High-intensity spacing prevents weeds.
Fertilize your kale once a month with fish emulsion, seaweed emulsion, or compost tea, or a high-nitrogen organic fertilizer. Kale plants will mature in about 50 to 65 days, depending on the variety. You can also pick leaves sooner; many people prefer small, tender kale leaves.
Special Tips for Growing Kale
Kale is pretty easy to grow once it’s established, but it prefers moist soil. Be sure your plants get at least 1 inch of water per week, either from regular irrigation or a lot of rain. Once your kale seedlings have reached 6 inches tall, give them a 2- to 3-inch layer of mulch to help retain soil moisture and keep the roots cool.
Let Kale Have Some Frost
Like most winter vegetables, the taste of kale improves greatly after it receives a few frosts. An extremely cold-tolerant plant, kale can be harvested as late as December in many areas, and will overwinter in warmer locations. If you grow it in a cold frame, you can harvest it all year long in all but the coldest climates.
Companion Plants for Kale
Kale is a great companion for artichokes, beets, celery, cucumber, lettuce, onions and garlic, peas, potatoes, radishes, spinach, cilantro and dill.
Kale will not do well if it is planted beside strawberries, sunflowers, beans, and other brassicas like broccoli or cabbage.
Kale Pests and Diseases
Kale is relatively easy to grow, but you might see the following issues. Be sure to practice good crop rotation, and not plant Brassica family crops in the same place the following year.
Leaves curl under and become wilted, deformed and yellowish.
Aphids are tiny, oval, yellowish to greenish pear-shaped insects that colonize on the undersides of leaves. They leave behind sticky excrement called honeydew which can turn into a black sooty mold. Use insecticidal soap.
Whiteflies are tiny, white flying insects that rise in a cloud when you disturb your kale plants. Use insecticidal soap or neem oil and spray every few days until they are gone.
Small holes or pits in the leaves.
Flea beetles are tiny pests that are dark in color, with a shiny, iridescent carapace. They jump like fleas when disturbed, earning the name flea beetles. Use floating row covers; mulch deeply around plants. Use diatomaceous earth or Neem oil to control the population.
Leaves with large chew holes.
Cabbage moths/worms are the most common pest that affects kale. These small green worms, sometimes called cabbage loopers, are the larvae of the little white cabbage butterfly, and will eat holes in the leaves of your kale, sometimes at an alarming rate.
To control cabbage worms, inspect plants regularly, and scrape away any eggs you see on the undersides of leaves. Pick worms off by hand and squish them, or use Bt (Bacillus thuringiensis) if you have a large infestation. A floating row cover can stop the cabbage butterflies from landing on your kale, and prevent them from laying their eggs.
Slugs and snails should be hand-picked with gloved hands and drowned in a pail of water. You can also easily lure them into traps made by placing an inch of beer in a small open container, and sinking it up to its rim in soil or mulch. You can also use copper tape around your garden beds, or diatomaceous earth to keep them away from your plants.
Spots on top of leaves with downy mold on the underside of leaves.
Downy mildew is a fast growing fungus affects that Brassicas, cucumbers, melons, peas and more. It first appears on older leaves as white, yellow or brownish spots on the upper surfaces and downy grayish mold on the undersides.
Prevent and control downy mildew by improving air circulation and keeping the leaves dry by using mulch and drip irrigation. (If you must use overhead sprinklers then water early in the morning or evening, so plants don’t stay wet all night.) Remove any infected plants promptly.
Spores overwinter on crop debris, so clean up your garden in the fall and rotate your crops every year. The spores can travel long distances on the wind, especially in moist air.
How to Harvest and Store Kale
Harvest baby kale at 25 days; mature kale at 50-65 days, depending on variety. Harvest by snapping off or cutting the older, outer leaves, to allow the center of the plant to continue producing.
For best flavor, harvest after a couple of frosty nights, as cold greatly improves the taste of kale. Kale leaves harvested in the heat of summer can be bitter and a little tough—best for long cooking, soups or stews.
Store Whole Bunches In the Fridge
Wrap a bunch of unwashed kale in a layer of paper towels, and store in a glass container, supermarket bag or a zip-top bag in the refrigerator crisper drawer. The kale should last for a week, maybe two.
Store Washed, Prepped Kale in the Fridge
Kale is one of the only greens that you can wash and prep days in advance without it molding or wilting terribly. You can stem and chop the leaves, wash them, dry them thoroughly in a salad spinner or with kitchen towels, and store the chopped kale wrapped in a paper towel in a glass container or zip-top plastic bag for up to 3 days.
Blanch and Freeze the Leaves
If you aren’t going to get to the kale within a week, you can freeze your kale leaves to use them in soups, baked dishes or green smoothies later on. To blanch kale, boil a large pot of salted water and prepare a large bowl of ice water. De-stem the leaves using a knife or your hands, and cook them in the boiling water until they brighten in color, 1 to 2 minutes.
Drain the kale in a colander, then quickly transfer the leaves to the ice water to cool. Dry the blanched kale thoroughly using a salad spinner or kitchen towels, then freeze the leaves flat on a baking sheet. Once frozen solid, store your kale in zip-top bags in the freezer for up to 8 months. You can add individual leaves straight from the freezer to your blender for smoothies and pestos, or chop them while frozen, and add them to soup and stews.
How to Save Kale Seeds
If you want to harvest seeds from your kale plants, you need to be sure to isolate the crop from any other Brassica varieties that it might pollinate with (including other kale varieties, cabbage, collards, broccoli, cauliflower, bok choi, etc.) by a distance of one mile or by using a seed isolation tent.
Because kale is a biennial, it will produce stalks of yellow flowers during its second year of growth. Let these flowers turn into elongated seed pods which you should allow to dry out on the plant. Gather the dried seed pods in a bag and let them dry even further indoors for a week. Once fully dry, shatter them and collect the largest seeds for planting.
Store your kale seeds in a cool, dry place and they should last for four to five years.
How to Use Kale
Kale is one of the most nutrient-dense foods that humans eat, so it’s great to incorporate into any healthy, whole food diet. A single cup of raw kale (about 67 grams or 2.4 ounces) contains:
- Vitamin A: 206% of the DV (from beta-carotene)
- Vitamin K: 684% of the DV
- Vitamin C: 134% of the DV
- Vitamin B6: 9% of the DV
- Manganese: 26% of the DV
- Calcium: 9% of the DV
- Copper: 10% of the DV
- Potassium: 9% of the DV
- Magnesium: 6% of the DV
Kale holds its texture well during cooking, and it can be steamed, sauteéd, roasted, or eaten raw. You can blend it into smoothies, wilt it into soup, bake it into kale chips, or process it into pesto.
It’s a good idea to remove the leaves from the middle rib or stem because it tends to be tough, fibrous, and bitter. Remove them by hand or with a knife or kitchen shears, and use the stem chopped up in stir-fries or smoothies, or simply compost it.