Kale suffers from a staid reputation. Gardeners appreciate its willingness to grow when and where other vegetables won't, and its healthfulness is legend. But this article speaks to kale's lesser-known but more potent virtue, namely its staggering genetic diversity. This cabbage relative is so diverse, its living presence so dramatic, and its ease of culture so universal, that it is bound to be an important vegetable into the next millennium.
Kale's diversity is an invitation to gardeners to experiment and explore. You'll find types suited to nearly every North American region with a cool growing season: from summer in Alaska to winter in Florida. If you live in the South or in a mild coastal region, kale offers a good introduction to winter gardening. And if your area stays above 0F (USDA Hardiness Zones 6b and milder), in addition to eating a lot of fresh kale in winter, you can gather the sweet, tender shoots in spring. Their flavor (lightly steamed) equals that of broccoli.
Getting to Know Kale
I've known about kale forever, it seems. My mother used to cook it for my father but never offered me any. Wise mother: why waste that delicious green on a child likely to reject it -- She also delighted in recounting how an old-time gardener liked to freeze so much kale for winter that she used her washing machine to get the dirt out of it. It wasn't until I was 25 that I cooked kale for myself, but by the time I was 30 I was selling 'Red Russian' kale seedlings, leaves, shoots, and blossoms to New York restaurants.
When people ask, "What is kale?" I usually reply, "Primitive cabbage." But a more precise (and complicated) answer is that kales are also primitive rutabagas.
The kale family, botanically the genus Brassica, includes three species with leafy forms -- probably close to those of the original wildings -- that gardeners call kale: B. oleracea, the wild ancestor of cabbage, broccoli, brussels sprouts, kohlrabi, and cauliflower, is from the Atlantic and Mediterranean coasts of Europe. The B. o. Alboglabra group includes the white-flowered Chinese kale. It's native to Southeast Asia. The kales that I work with most are B. napus. This species includes rutabaga, 'Red Russian' kale, and rape and is widely adapted and distributed in northern Eurasia, though its native region is unknown.
Compared to its more famous relatives, such as broccoli, cabbage, and kohlrabi, only kale retains the dignity of a well-rounded aboriginal.
A hundred years ago, kale filled a bigger niche in most people's lives. Before refrigeration and long-distance shipping, kale was a cold-season staple. Chickens thrived on it, and cattle had their own named types.
The classic 1885 catalog, The Vegetable Garden, by the French horticulturist Vilmorin, listed 26 kale or borecole varieties. These included perennial kales, kales with swollen edible trunks (marrowstem kale), kales for all seasons of production, and kales bred for their broccoli- or asparagus-like shoots. One example is Vilmorin's 'Jersey Kale', also called tree cabbage. It lived for three springs and reached 9 feet tall! After its flowering tip was snapped away and given to the cattle, the woody stem could be fashioned into a strong, lightweight, and very classy walking stick.
Few of the varieties listed in The Vegetable Garden are widely available today, and many are probably extinct. One exception is 'Palm Tree Borecole', now making a comeback as 'Lacinato' or 'Cavolo Palmizio'(palm cabbage). We've grown this for several years, and it's won acclaim from everyone who's tried it, including our 5- and 7-year-old boys.
Renee Shepherd, owner of Renee's Seeds, Felton, California, described 'Lacinato' affectionately as "dinosaur kale" for its primitive appearance. The dark blue-green leaves are 2 to 4 inches across and sometimes more than 2 feet long, and have none of the curls and frills common in kales. Rather, the leaves are rumpled and puckered like savoy cabbage (certainly part of its heritage) and curled under along the entire margin. 'Lacinato' is a stout and substantial kale used for Tuscan soups and stews.
'Red Russian' has done more than any other variety to enhance kale's image. This heirloom (a variety of B. napus) is essentially a rutabaga developed for its top growth rather than its root. It began reappearing in catalogs around 1980. Among its major advantages, it's good raw in salads, and its oak-shaped leaves -- in colors ranging from blue-green to purple-red -- show off in edible landscapes and mesclun salads. Cold weather intensifies its color, and it will survive winter lows of 0° F to produce a large crop of purple-stemmed sweet shoots in spring.
'Winter Red' is a newer 'Red Russian' type with great winter vigor, color, and flavor. 'Ragged Jack' is similar to 'Red Russian' but lacks its winter hardiness.
Two other heirlooms, 'Tall Green Curled' and its compact form 'Dwarf Green Curled', have set the kale standard (green, frilly, upright leaves) since before 1865 and are still available.
In 1950, researchers at the Virginia Truck Experiment Station introduced 'Vates Dwarf Blue Scotch Curled', which is the most widely grown kale in the United States. 'Konserva', a Danish variety, and the Dutch 'Westlandse Winter' are the standard varieties in Europe. Both have dark green, well-curled leaves on 24-inch plants. 'Verdura', a hybrid of 'Westlandse Winter', is available in the United States. Another hybrid, 'Winterbor F1' is noted for its high yields, cold hardiness, uniformity, and ruffled green leaves on vigorous 3-foot-tall plants.
Exciting New Kales
In the seed trade, the most prominent new B. oleracea kale is 'Redbor F1', a stunning 3-foot-tall hybrid from the originator of 'Winterbor'. Its warm-season growth is a mass of well-curled reddish leaves with deep purple veins, which turn a solid, deep violet in cool weather. 'Redbor' is everything you would want in an ornamental cooking kale: showy, vigorous, and healthy. So how is its flavor-- When it was lightly steamed and tasted against the ancient 'Lacinato' and the genetically diverse Wild Garden kale (see below), three adults and two children judged it a distant third.
The first kale I grew was 'Siberian', a B. napus variety with gray-green ruffled leaves and great hardiness; it's widely grown as a winter crop in the southern United States. 'Red Russian' came into my life a few years later, about the time I began saving seed. My first cross between these two soon appeared, and their undisciplined progeny soon infiltrated my garden, my commercial salad greens, my meals, and my seed collection. By now, these progeny have been sorted into a number of varieties that are among the newest kales in the seed trade.
For instance, National Gardening vegetable variety testers chose 'Red Ursa' as one of this year's top 10 new varieties. This red-veined, ruffle-margined kale is an intermediate form between 'Red Russian' and 'Siberian'.
Montana-based Garden City Seeds introduced my 'White Russian'in 1996 after two years of trials proved it to be the only kale to overwinter in the company's test garden. It was also the only kale to thrive after repeated winter flooding at Gathering Together Farm in Philomath, Oregon, where the seed is produced. Field crews at both facilities voted 'White Russian' the best-flavored kale.
Renee Shepherd was the first seed dealer to test my Wild Garden kale. Wild Garden kales are not really a distinct variety; they're a strain, or what I prefer to call a "gene pool," derived from the original cross between 'Red Russian' and 'Siberian'. Wild Garden kale includes about as much diversity as you can work into a packet of seed, so much so that other unique varieties have been produced from it. Examples are 'Purple Rapini', a flat-leaved, purple-veined kale that makes prodigious spring shoots, and unnamed, frilly green or violet forms that resemble the kale engravings from Vilmorin's The Vegetable Garden. Among Wild Garden kales, you'll also find savoyed (curled, wrinkled), puckered, and fringed leaves in every hue from gray-green to lime to violet to red.
Years ago I gave friends at Gathering Together Farm a sample of Wild Garden kale. Out of that, they selected their favorite red types, with leaf forms from flat to ruffled to frilly, and saved seed. The result is their Wild Red kale, an open-pollinated strain that they have sold for years at wholesale and local markets. Bunches of Wild Red look like vegetable bouquets on the produce rack, and they're great examples of kale's genetic diversity being put to commercial advantage.
You can do the same. A packet of Wild Garden kales is an opportunity to experience the genetic diversity of kale, then select and save seed of the types suited to your own place, purpose, and flavor preferences.
When, Where, and How to Plant
In western Oregon, we sow seed in the last half of July. Gardeners in colder climates should sow earlier, and those in milder areas a little later. It's better to grow kale slowly through the warm periods, so it will be hardy into the post-frost season, when the flavor is best. Space plants 14 inches apart in all directions, or 12 inches apart in rows 2 feet apart. Most kales will grow into whatever space is provided, having larger leaves and thicker shoots as more room is available. Plants mature in 50 to 80 days.
Soil, water, nutrients. Growing requirements are about the same as those for cabbage: fertile soil, neutral pH, plenty of calcium, and water as needed. Excess nitrogen will cause sappy, frost-sensitive tissues.
Saving your own seed. By letting kales progress beyond the leafy stage, you get to try the delicious broccoli-like flowering shoots. They're so numerous and persistent, you'll always have plenty that go beyond the bud stage. These flowering buds make excellent edible blossoms to garnish salads and soups, and you'll find blossoms abuzz with bees and beelike syrphid flies. The earliest seed is ready by July, when the pods begin to turn dry and brown.
Pests and diseases. Botrytis (head rot) and black rot are the only diseases we find in our location, though kale may contract other diseases that affect the Brassica genus in your area. Botrytis causes leaves and the growing point to break down during wet, cold weather. Black rot causes spotting on leaves before the plant is mature. Both diseases are seed-borne and spread by spores on the wind or in the soil.
Cabbage aphids can be troublesome to drought- or heat-stressed plants at the end of summer. In our garden, syrphid fly larvae are major aphid predators on autumn kale. If these or ladybird beetles aren't doing the job, spray insecticidal soap, or blast the aphids away with a spray (high pressure, low volume) from the hose.
You may see greenish or yellow-green syrphid fly larvae among the aphids, chomping a hole right through the colony. In time these larvae will mature into hover fly or bee fly adults. Syrphid adults are very keen on kale flowers, where they drink nectar, mate, and eat the pollen that's required for egg laying. You see their white, rice-shaped 1/16-inch-long eggs attached to aphid-infested leaves, where the larvae will emerge and begin to dine.
If you find brassy-colored aphid "mummies," this is a sign that tiny parasitic wasps are aiding your efforts, and more of these beneficial wasps will soon hatch out of the parasitized aphids. Leave the mummies in place.
Besides its good looks, flavor, and benefits to garden ecology, kale is good food. To get more protein from a green, you'd have to eat nettles; to get more calcium, you'd have to eat lamb's quarters; to get more iron, you'd have to eat amaranth or purslane; to get as much vitamin A, you'd have to eat dandelions. You can't get more vitamin C from any other leafy green. And don't forget the benefits of fiber, and the kale family's proven reputation for anti-cancer properties.
So remember: Kale has roots deep in the horticultural soul. Kale is widely adaptable. Kale is easy to grow and provides harvest opportunities at almost all stages of its growth. Kale creates a supportive environment for several beneficial insects. Kale can be enjoyed raw or cooked. Kale might even change your life.
Photography by Suzanne DeJohn/National Gardening Association
Article published on June 23, 2008.