Kale (Brassica oleracea) is essentially a form of cabbage that doesn't have the tightly formed head associated with most cabbages, and it's grouped in the cooking greens category with collards, mustard, and Swiss chard. Kale plants can be quite ornamental, with textured and curly leaves that come in shades of green, purple, and other colors.
Kale has a relatively fast growth rate and can grow from seed to harvest in about three months. It is best planted in the late winter or early spring and can also be planted in the late summer for a fall-to-winter harvest. This biennial plant takes two years to complete its growth cycle—so it grows leaves in its first year, while seeds and flowers develop in its second growing season.
|Common Name||Kale, ornamental kale|
|Botanical Name||Brassica oleracea|
|Plant Type||Annual, biennial, vegetable|
|Mature Size||1–2 ft. tall, 1–2 ft. wide|
|Sun Exposure||Full sun, partial sun|
|Soil Type||Loamy, moist, well-drained|
|Hardiness Zones||7–9 (USDA)|
How to Plant Kale
Kale is a fast-growing vegetable that does best in a planting location with full sun. Plant kale seeds about 1/2 inch deep, leaving at least 1 1/2 to 2 feet between each plant. High nitrogen content in the soil is important for kale to grow its leaves, so adding a few inches of organic matter like compost to a well-draining soil mixture will encourage a healthy harvest.
When to Plant
Kale can be planted three to five weeks prior to your area’s projected last frost date in the spring. In most regions, gardeners can harvest kale in the summer by planting it at this time. It can also be planted in late summer roughly six to eight weeks before your first fall frost.
Those in warm climates (zone 8 and above) can continue to plant in the early fall for a late fall to winter harvest. Kale takes roughly three months to reach maturity from seed, while cuttings will mature in about one month.
Selecting a Planting Site
Kale grows equally well in pots, garden soil, raised garden beds, and other containers. Kale can grow indoors as long as you have adequate lighting. Soil that’s rich in organic matter and has sharp drainage is ideal, and the planting site also should get ample sunlight. Be sure the kale isn't too close to taller plants that will shade it. Growing kale in a window box can also be successful in south- or west-facing windows, but in very hot climates, east-facing windows can help prevent scorching from the afternoon sun.
Spacing, Depth, and Support
Space kale plants roughly 1 1/2 to 2 feet apart, and plant them at the same depth they were growing in their nursery container. Seeds should be planted around 1/2 inch deep. No support structure is necessary.
Kale needs full sun to partial shade in most climates, as the fullest growth will occur when the plant gets six or more hours of direct sunlight on most days. However, if you live in a hot, dry climate, provide your plant with some shade, especially from the strong afternoon sun. Heat can make the leaves wilt and lose their flavor.
Kale plants like to grow in a rich soil that's high in organic matter with a slightly acidic pH (6.5 to 6.8). The high nitrogen content provided by organic matter is crucial for healthy leaf growth. The soil also should drain well.
Kale needs a consistent amount of water to stay healthy, generally growing best in 1 to 1 1/2 inches of water per week. Water your kale plants regularly to keep the soil evenly moist but not soggy. Along with cool temperatures, moist soil helps to keep the kale leaves sweet and crisp, rather than tough and bitter. Mulching around your plants can help to keep the soil cool and to retain moisture.
Temperature and Humidity
The plant is usually considered a cool-weather vegetable and can handle some frost once they're mature. The optimal soil temperature for planting kale is 60 to 65 degrees. All varieties prefer cool temperatures and will be sweetened by a touch of frost. Hot weather turns kale bitter. Kale is a biennial plant, taking two growing seasons (or years) to complete its life cycle, but it's usually grown as an annual. It will collapse if exposed to heavy frosts or snow. But it can be grown throughout the winter in USDA zones 7 through 9 if the winters are mild and there is adequate water.
When planting, mix fertilizer into the top 3 to 4 inches of soil. Then, feed your kale throughout the growing season, following the instructions on your fertilizer label. Use compost or a high-nitrogen vegetable fertilizer.
Types of Kale
There are many kale varieties, and they're all worth a try. The curly-leaf varieties tend to hang on longer in cold weather. But the flat-leaf types generally become established faster. Here are some varieties to consider:
- 'Hanover Salad' is a fast grower and an early producer. It has a pleasant taste for eating raw in salads.
- 'Lacinato' is a puckered heirloom kale from Tuscany. It is sometimes listed as Tuscan or dinosaur kale. Its thick leaves are hardy enough to be harvested even after a snowfall.
- 'Redbor' has magenta leaves with curly edges. It features a mild, crisp flavor and texture.
- 'Red Russian' has smooth, tender leaves with purple veins and edges. It is considered one of the sweetest varieties of kale.
- 'Vates' is a dwarf, curly, bluish-green kale that is both heat- and cold-tolerant. It is derived from 'Dwarf Blue Curled Scotch' kale.
Kale vs. Chard
Kale and chard have similar appearances. Their leaves are often large, crisp, crinkled, and deep green. Their difference comes in their taste. Kale is generally stronger, with a bitter and earthy flavor. And chard is a much milder green. Plus, kale’s thick stems are typically best removed before eating while chard’s stems may be tenderized by cooking them.
Expect to wait approximately two months for your kale plants to mature from seeds. Check the days to maturity on your seed packet or plant label for more precise timing. Spring-planted kale will be good for harvesting throughout the summer months, but it's especially tasty after a light frost.
You can harvest young kale leaves to use fresh in salads or allow your plants to mature for use as a cooked green. Remove the older outer leaves, and allow the center of the plant to continue producing. Kale will keep in the refrigerator, ideally in the crisper drawer, for about a week.
How to Grow Kale in Pots
Kale is easy to keep in pots. Not only does this make the plant mobile so that you can move it into adequate sunlight and protect it from severe weather as needed, but it also helps to protect it from garden critters, such as rabbits, that might munch on the leaves. Plus, container growth is ideal if you don’t have garden space or the right soil conditions.
Select a pot with at least a 12-inch diameter. It also should have ample drainage holes. An unglazed clay container is a good option because it will allow excess soil moisture to escape through its walls, helping to prevent root rot. Use a quality potting mix; an organic mix made for growing vegetables is a good option. Transplant your kale into the pot at the same depth it was growing in its previous container, and water it after planting.
Though it's typically unnecessary to prune kale, you may want to cut it back to the ground if there is a pest infestation in the upper leaves of the plant. For kale that is trying to bolt, pruning will not slow down this process. You can eat the bolted leaves because they are less bitter than other bolted greens.
Kale is most commonly planted from seeds or nursery plants, but it can also be propagated via cuttings. Kale does regrow after cutting, but it requires a specific propagation process. To pick kale to keep it growing healthy, cuttings must be taken from the oldest leaves. Here’s how:
- Use gardening shears to cut a stem from the bottom of the plant on its side, choosing one with multiple leaves from the main stem (do not propagate from the plant's center). Remove the leaves on the lower half of the stem. Trim the bottom of the stem right below a leaf node at a 45-degree angle.
- Dip the cut end in rooting hormone.
- Plant the bottom half of the stem in a moistened soilless potting mix in a small container with drainage holes.
- Continue to keep the growing medium moist. Roots should develop in a few weeks. If you can gently tug on the stem and feel resistance, you’ll know roots have formed. After that, it’s ready for transplanting.
How to Grow Kale From Seed
Growing kale from seed can begin inside or outside depending on your region. Kale can be direct seeded in the garden or started indoors and transplanted into the garden. You can direct seed in cold climates as soon as the soil temperature is at least 45 degrees Fahrenheit.
- Start plants indoors in a seed-starting mix about six weeks before your last expected frost date. Kale seeds germinate quickly in warm soil and should sprout up within five to eight days.
- Cover the seeds with about 1/2 inch of soil, and keep the growing medium moist.
- Transplant your seedlings from indoors after the danger of frost has passed.
Common Pests and Plant Diseases
Kale is a member of the cabbage family, which is notorious for attracting insect pests and for rot diseases. Kale is susceptible to black rot and clubroot, as well as aphids, cabbage loopers, cabbageworm, cutworms, flea beetles, and slugs. The best defense is to monitor the plants often for signs of eggs or feeding, such as holes in the leaves. Treat problems as soon as they arise.
Is kale easy to grow?
Kale is an easy vegetable to grow, as long as it gets sufficient light, water, and nutrients.
How long does it take kale to grow?
After planting seeds, kale will be ready to harvest in about two months.
Can you grow kale indoors?
Kale can be grown indoors, though you'll likely need a grow light if you don't have a window that gets lots of direct sun.
Kale. Cornell University Growing Guides.