By Dr. Mercola
Kale1 — a well-recognized "superfood" — is rich in healthy fiber and antioxidants, and is one of the best sources of vitamin A, which promotes eye and skin health and may help strengthen your immune system, and vitamin K.
A 1-cup serving has almost as much vitamin C as an orange and as much calcium as a cup of milk. It's also an excellent source of lutein and zeaxanthin (which help protect against macular degeneration), indole-3-carbinol (thought to protect against colon cancer by aiding DNA repair), iron and chlorophyll.
One serving of kale also contains 2 grams of protein, 121 milligrams (mg) of plant-based omega-3 fats, 92 mg of omega-6, and — like meat — all nine essential amino acids needed to form proteins in your body, plus nine nonessential ones for a total of 18. Studies suggest kale can help lower total cholesterol and LDL cholesterol while raising HDLs, lowering your risk for heart disease. Kale has also been shown to provide "comprehensive support" for detoxification by regulating the process at the genetic level.2
Kale Is Simple to Grow and Provides Ornamental Beauty
Unfortunately, conventionally-grown kale is frequently contaminated with high amounts of pesticides,3 making it important to buy organic. Better yet, grow your own!
As little as three or four plants can supply enough greens each week for a family of four, and the plants grow well in containers if you don't have a backyard. Many gardeners appreciate kale for their ornamental value as well. Growing your own will also give you better control over soil conditions.
Are Concerns About Thallium Toxicity Valid?
Like many other greens, kale tends to concentrate toxins present in the soil, and thallium toxicity has been reported even in organically-grown kale. Media warnings about "kale poisoning" erupted two years ago after private experiments by molecular biologist Ernie Hubbard suggested people were being exposed to dangerous levels of heavy metals from plants like kale.
The story broke in the magazine Craftmanship Quarterly.4 Huffington Post was one of the few news sources trying to clarify the media miscommunication that followed, noting the errors in journalism.5 Anna Almendrala wrote, in part:
"Hubbard, an unaffiliated scientist from Marin, California, who works at an alternative health clinic, has been testing local kale and soil and has arrived at the conclusion that the cruciferous vegetable's ability to 'hyperaccumulate' the heavy metal thallium is posing a health risk to his community.
Hubbard tested levels of thallium in vegetable samples and in the urine of people from Marin … who have complained of things like fatigue, brain fogginess and nausea. The symptoms are signs, he said, that they may be experiencing low-level heavy metal poisoning.
These signs, however, are correlative, which means Hubbard doesn't know for sure if crucifers have caused the symptoms or if something else may be at play. But this hasn't stopped other outlets from recommending that their readers cut back on certain vegetables …
[T]here's no reliable evidence to suggest you should kick your kale to the curb, confirmed Shreela Sharma, a registered dietitian and associate professor in the department of epidemiology, human genetics and environmental sciences at the University of Texas Health Science Center at Houston.
Hubbard acknowledged the limitations of his research to HuffPost, and wrote in an email that he never intended for his preliminary results to stand on their own, without corroboration, as a prescription for the general public."
It's important to realize that nutrient and contaminant uptake go hand in hand, and if there's a thallium problem, it's really a soil quality issue, not a kale plant issue per se. If you grow your vegetables in clean, healthy soil, you will not have heavy metals in your food, by virtue of there not being any in the soil for the plant to take up.
Kale Breeding Program Promises Greater Variety
There are many different varieties of kale, providing different colors, textures and tastes. Cornell University is also working on a program to identify and breed consumer favorites, based on shape, color, flavor and texture. As reported by Science Daily:6
"Griffiths and Swegarden are focusing efforts on developing new kale cultivars, including the evaluation of hybrid combinations. New cultivars in Griffiths' breeding pipeline will push consumer expectations for kale, blurring the current color boundaries of greens and purples and introducing a range of new leaf and plant shapes …
As part of the program, Swegarden has been gathering feedback from seed producers, growers, supermarket managers and consumers … She is partnering with Cornell's Sensory Evaluation Center to perform consumer trials to develop a consumer kale lexicon and establish a trait hierarchy that can be used to guide the breeding program.
This data will determine which hybrids and breeding lines to select in the field. Swegarden predicts that in the next few years consumers will see an even richer diversity of leafy greens available to them."
Popular Kale Varieties
The oldest variety of kale is curly kale, which has ruffled leaves, a deep-green color and a bitter, pungent flavor. More recent varieties are ornamental kale, Russian and dinosaur kale, the latter of which has blue-green leaves and a more delicate taste than curly kale.
Ornamental kale, sometimes called salad savoy, was originally used as a decorative garden plant (it comes in green, white and purple colors), although it can also be eaten and has a mellow flavor and tender texture. As a general rule, kale with smaller leaves tends to be more tender and milder than larger-leaved varieties. While there are many options, some of the more popular varieties of kale include:7,8,9
- Red Russian, a frost-hardy, slug-resistant variety that is sweeter than most other kinds of kale
- Dinosaur kale (aka Tuscan kale or Lacinato), another sweet-tasting variety with large, puckered blue-green leaves
- Hanover Salad, a fast grower that produces an early harvest
- Redbor, a magenta-colored, curly-edged variety with mild flavor and crisp texture
- Vates, a dwarf kale with curly, blue-green leaves that can tolerate both heat and cold
Kale Is an Ideal Cold Temperature Crop
As a general rule, kale tastes best when grown in cooler temperatures. Warm weather (or summer crops) produces more woody and bitter-tasting greens. Optimal soil temperature is in the 60- to 65-degree F range, but you can direct-seed into your garden as long as the soil temperature is at least 45 F.
To harvest before the worst summer heat has a chance to take its toll, start seeds indoors approximately six weeks before your last frost date.10 Transplanting seedlings into your garden can speed up the maturation process from an average of 55 to 75 days to as little as 30 or 40.
For a fall crop, plant seeds about eight weeks before your first frost date. Kale is cold tolerant, and if you live in the north, you can harvest even after a light snowfall. Most can thrive in temperatures as low as 15 degrees F, giving you the option of cultivating a winter crop.
Sow seeds at a depth of about one-half inch. Keep moist but avoid overwatering as this may cause the seeds to rot. Germination typically takes about 10 days. Thin the plants once they're 3 to 4 inches tall, leaving only the healthiest-looking ones. Once the seedlings are about 9 inches tall and four leaves have developed, they're ready to be transplanted into your garden.
General Growing Tips
• In the early spring and fall, plant your kale in full sun. If you're growing it during the summer, be sure the plants have partial shade. Use straw or mulch to preserve moisture and prevent the roots from excess heat. Just beware that kale will not generally thrive in the summer, and will be far more bitter than a fall crop grown in a cooler climate. Kale tends to become more attractive to pests during the summer as well
• Kale tends to prefer slightly acidic soil that is high in nitrogen. Make sure the soil drains well, but keep moist to avoid stunting the plant's growth. Lack of moisture will also render the leaves tough and bitter
• Dress with compost every six to eight weeks. Growth can be further boosted by adding a seaweed or fish emulsion once a month
• Give each kale plant 12 to 24 inches of space to allow sufficient airflow
As a member of the cabbage family, kale is prone to rot diseases like black rot, club rot and wirestem, and while far more disease-resistant than many other vegetables, common pests include aphids, cabbage loopers, cabbageworms, cabbage root fly, cabbage whitefly, cutworms, flea beetles and slugs.
One of the easiest ways to protect young kale from many of these pests is to use a featherweight row cover. Once you remove the row covers, check your plants often for signs of pests and disease.
Harvesting, Storage and Cooking Suggestions
Your kale is ready for harvest once the leaves are about the size of your hand. Harvest by nipping the outer leaves off from the stem. Be sure to leave the center leaves to ensure continued growth. As a general rule, you can harvest three or more leaves from each plant every five days. Remove any yellowing or wilted leaves, as leaving them on the plant will encourage pests.
Kale has a relatively short life in terms of crispness, so it's best to use within a few days of harvesting, although the leaves can be blanched and frozen for long-term storage. Kale chips are another popular alternative that will lengthen their shelf life. Here's a simple kale chip recipe:
- 6 cups of torn and de-stemmed curly kale
- 2 teaspoons coconut oil, grass fed organic butter or ghee
- 1/4 teaspoon Himalayan salt
- Nutritional yeast to taste
Optional: 1 pinch sweet or smoked paprika, chili powder, garlic powder or onion powder
- Wash and spin dry the chopped, de-stemmed kale. It's important that the kale is completely dry before baking
- Toss together the kale and coconut oil. Massage together with your hands until every leaf is coated
- Sprinkle on salt, nutritional yeast and any seasoning you will be using. Toss again to evenly distribute
- On a parchment-lined baking sheet, arrange the kale evenly without crowding or overlapping
- Bake in a 300-degree F oven until crisp and dark green, approximately 12 to 15 minutes
- Cool completely before eating. This will allow the chips to crisp up
Kale is versatile in that it can be used either raw or cooked, and makes for a great addition to a wide variety of dishes. Cut smaller, paler green leaves into fresh garden salad; use the larger, dark greens for stir-fries or soup. For even more serving suggestions, see my previous article, "9 Healthy Kale Recipes." You can even eat kale for breakfast. Instead of eating an egg, try this quick and easy breakfast kale stir-fry:
- Chop up half a bunch of kale, a quarter of an onion, and stir-fry in a tablespoon of coconut oil for a few minutes until the leaves are tender
- Add pinch of sea salt or Himalayan salt, a pinch of pepper, a teaspoon of lemon or Ume Plum Vinegar and some dulse flakes