How to Grow Kale

This cool-weather, leafy green is ideal for a cut-and-come-again harvest.

Farm worker inspecting organic kale leaves
Ron Levine / Getty Images

Kale has been the health-food darling for a while because even for the brassica family, it is exceptionally rich in antioxidants, iron, and phytonutrients. This cool weather, leafy vegetable ranges from dark red to purple to deep bluish-green colors and can have flat leaves with ruffled edges, dinosaur-skin texture, or fully frilly leaves. Loose-leaf foliage grows outward from a central stem, making kale ideal for a cut-and-come-again harvest for the home gardener. And since kale has been showing up on the “Dirty Dozen” list of pesticide-laden veggies, it may be worth the (light) effort to grow your own.

How to Plant Kale

Kale can be planted in fall ahead of cool weather and indoors in winter to get an early start in spring, and again in late spring for a fall crop. Timing is fairly important, as conditions need to be warm enough for the young plant to sprout and stay alive, but not so warm that the plant bolts before you can enjoy it.

What Is Bolting?

Bolting is the production of a flowering stem on cool-weather greens, triggered by warm temperatures that signal the end of a crop's annual growth cycle. When this occurs, the "bolted" stem produces seeds too early for harvest, and its leaves usually turn tough and bitter.


Growing From Seed

After your area’s last frost date, plant seeds 12-16” apart, about ¼” deep (a little deeper if needed to keep seeds moist). Plant again in late spring/early summer, and again in fall for a winter crop.

Planting too many rows of brassicas close together can attract damaging insects, so it may be helpful to separate them and/or interplant with herbs that attract pest predators or alliums (garlic, chives, etc.) that repel pests.

Growing From a Starter

Plant in flats 4-6 weeks ahead of your transplant date, keeping soil temperature around 75 degrees F until germination. Then, lower the air temperature to around 60° F to acclimate seedlings to the cooler environment they prefer. When they have a few true leaves, plant as above for seeds.

Growing Indoors and in Pots

It is possible to grow kale indoors if you keep your home on the chilly side and have a very sunny location. An unheated sunroom might work well.

Kale Plant Care

Kale is remarkably hardy and not fussy, and once it gets going, it needs little extra care except for pest control. 

Light

Kale needs mostly full sun, but leafy greens grow better with a little shade during the day than with full, burning sun.

Soil and Nutrients

Like other brassicas, kale prefers a neutral to slightly alkaline, loamy soil with lots of organic matter, so adding compost and mulching will benefit your kale. One study found that a previous cover crop of ryegrass or fava beans improved the biomass and nutritional value of kale.

Water

Cool-weather growing requires less water than summer tomatoes, as expected. Still, it's important to actively avoid water and heat stress in your kale plant, which will help to maintain good flavor without unpleasant bitterness. About an inch of rainfall, or the equivalent amount of water, per week is ideal. Sandy soil that doesn’t retain water requires more than one watering per week. Use a moisture meter to make sure water is reaching down to the kale's taproot.

Temperature and Humidity

Though some kale is cold-proof down to freezing, kale’s leaf mass, beta carotene, and lutein all increase as air temperature rises to 68 degrees F, and decrease as the air temperature increases further, according to a study. While kale tolerates a fairly wide range of temperatures, timing outdoor planting or regulating greenhouse temperatures will improve nutritional value. 

Common Pests and Diseases

There are a few critters to watch out for when growing kale. Cabbage worms, for one, are the green “inch-worm” larva of those cute white moths that flutter around and appear harmless. Don't be fooled — they will devour whole leaves before you know it. After planting kale, check daily for eggs and worms.

Harlequin bug, or Calico bug, is a shield-shaped stink bug that damages plants by sucking the sap out of stems. If brassica plants are not pulled immediately after harvest, these red and black bugs will have a field day with your kale, collards, and broccoli. They are easy to spot but quickly drop off the plant when they sense a threat. Keep weeds away from the base of your kale, so they don't have a hiding place. Knock them off the plant into a bucket of water with a bit of dish soap. The eggs of this bug look like little sushi rolls on the underside of the leaf and should be removed immediately. The University of Maryland Extension suggests floating row covers to exclude them, insecticidal soap, or using cleome as a trap crop.

Aphids are another sap-sucking pest that is partial to the kale leaves, especially the crinkly ones. If it’s feasible, blast them off with a forceful spray of water daily for several days in a row. Insecticidal soap is another option. A study found that intercropping herbs such as coriander, green onion, and parsley attracted plenty of aphid predators, such as spiders, causing aphids to disperse and therefore reducing the damage to plants.

Overwintering

If kale is planted in early fall, it should be able to stay alive through a mild winter. Mulching around the plants will help protect them. Keep in mind that in cold weather, if overwintering birds find no other food, they will snack on tender, leafy greens. If this is a concern, keep your feeder full, so the birds don't resort to munching on your crops.

Kale Varieties

Red kale leaves on gray
Red Russian kale. Yingko / Getty Images
  • Lacinato/Toscano kale has bumpy, crinkly leaves that are tender but hold up to cooking. Since its texture looks like an ancient reptile's skin, and it is nicknamed "dinosaur kale", it is the most likely to succeed with kids.
  • Red Russian is a flat-leaf type with curly edges. Its lilac-colored stems and purple-tinged foliage are striking, and the leaves are more tender than curly types. 
  • Curly leaf’s scratchy textures benefit most from cooking or “massaging”. The Redbor varietal is a deep magenta color, while the curly Siberian type is one of the most cold-resistant.
  • Walking stick kale stands out from other types of kale (literally) due to its tall stem, which can be dried, treated, and used as a cane, hence the name.
  • Tronchuda is a Portuguese varietal that has leaves like collard greens that form a cabbage-like rosette (not as dense). It tolerates heat better than other kales.
  • Ornamental kales form poofy, showy, cream and pink heads and make good borders or spots of color in rock gardens.

How to Harvest, Store, and Preserve Kale

Harvest kale in cool weather, as the texture and flavor decline with heat. Whether you harvest whole plants or cut just enough for dinner, the best way to keep greens fresh is to plunge them immediately into very cold water for several minutes, allowing them to absorb water and plump up their cells. Eliminate excess water with a paper towel or salad spinner before refrigerating.

For long-term storage, you can use a dehydrator to dry the leaves. Then, run them through a coffee mill or blender, and sprinkle on everything for a nutrient boost, or make your own instant soup mix.

View Article Sources
  1. Thavarajah, Dil, et al. "Effect of Cover Crops on the Yield and Nutrient Concentration of Organic Kale (Brassica Oleracea L. var. acephala)." Scientific Reports, vol. 9, no. 10374, 2019, doi:10.1038/s41598-019-46847-9

  2. Lefsrud, Mark, et al. "Air Temperature Affects Biomass and Carotenoid Pigment Accumulation in Kale and Spinach Grown in a Controlled Environment." HortScience, vol. 4, no. 7, 2005, pp. 2026-2030, doi:10.21273/HORTSCI.40.7.2026

  3. Regia, Ana, et al. "Intercropping Kale with Culinary Herbs Alters Arthropod Diversity and Hinders Population Growth in Aphids." HortScience, vol. 53, no. 1, 2018, pp. 44-48, doi:10.21273/HORTSCI12010-17