Growing kale in winter: How to plant, grow, and protect winter kale

Kale is a cold season superstar, thriving in the spring, autumn, and yes, even winter garden. We harvest a handful of hardy kale varieties throughout the winter months for salads, chips, smoothies, and soups. Depending where you live, winter kale can be left in the open garden or grown in a season extender like a cold frame, mini hoop tunnel, or greenhouse. And the best part is that kale is an easy-to-grow green that forms beautiful, productive plants. Below you’ll find everything you need to know about growing kale in winter.

Why grow kale in winter

There are many reasons to consider growing kale in winter. First, this non-heading member of the cabbage family boasts nutrient-dense leaves high in vitamins and minerals. It’s also extremely hardy with the most cold tolerant varieties surviving down to -10 F (-23 C)! Kale, along with beets, carrots, and leeks, also tastes better in winter, or at least after a couple of hard frosts. This is because the starch molecules in the plants convert to sugar molecules when the weather is cold. So winter = sweeter kale. Finally, kale is one of the easiest vegetables to grow in garden beds and containers and thrives with little fussing.

The impact of day length when growing kale in winter

While you can harvest kale all winter long, you’ll notice the plants don’t put on much new growth over the winter months. This is because plant growth slows when the day length falls below 10 hours a day. For me, that happens in early November. The kale plants then ‘hold’ in the garden or their season extenders until we harvest. It’s therefore important when growing kale in winter to plant at the right time so that your crop is the proper size when the days get dark and cold. More on that below.

When to plant kale for winter harvesting

The kale that I harvest in winter may be plants from the previous spring, summer-transplanted kale, or a fresh crop of baby kale greens that were direct sown in early autumn. Here is a closer look at when to plant kale for winter.

• Spring planted kale – Cold hardy kale is one of the first vegetables I tuck in my raised beds in early spring. These plants provide us with plenty of tender kale leaves from mid-spring through late autumn, and into the winter months if they’re protected with season extenders. The advantage of letting spring kale stay in the garden all season long is that by late autumn the plants have sized up nicely and are packed with leaves.
• Summer planted kale – Gardeners who want a winter kale harvest can also direct seed or transplant kale into the garden in mid to late summer. I typically transplant 3 to 4 week old kale seedlings in my raised beds in July for winter harvests. Most types of kale take 50 to 60 days to mature from direct sowing, or 40 to 50 days to mature from transplanting. You’ll want to time your summer planting so that the plants have reached maturity when the first fall frost arrives. Be sure to read the seed packet or catalog for specific ‘days to maturity’ information.
• Early autumn planted kale – While it’s nice to have a supply of large kale leaves for soup and chips, I also love baby kale leaves for salads. It’s quick and easy to grow and most varieties only need 4 to 5 weeks to yield a dense crop of immature leaves. Baby kale is harvested when the leaves are 3 to 5 inches in length.

How to plant kale seeds or seedlings for winter harvesting

Kale grows best in full sun with fertile, well-draining soil. I topdress the bed with 1 to 2 inches of compost or aged manure prior to planting. You can direct seed or transplant kale in the garden or into season extenders. For a crop of tender baby greens, it’s best to direct sow. Plant the seeds a 1/2 inch deep and 1 inch apart in bands or blocks. For mature kale, direct sow seeds 3 inches apart, thinning to 12 inches when the seedlings are 3 to 4 inches tall. Eat the thinnings, or transplant them to a different spot in the garden. If transplanting kale seedlings into your vegetable beds, space them 12 inches apart.

Growing kale in winter

One of my favorite things about growing kale in winter is that there is little work to do in the winter garden. I harvest, but once the cold weather has settled in, I don’t need to weed, water, or worry about pests. Of course I do need to weed, water, and watch for pests in summer and autumn when the plants are actively growing. Kale requires consistent moisture to produce tender, mild-flavored leaves. Drought stressed plants tend to be bitter, so water often if the summer or autumn weather has been dry. You can also mulch plants with straw to hold soil moisture.

I also fertilize kale plants monthly in summer and early autumn with a liquid organic fertilizer like fish emulsion to promote healthy plant growth and plenty of leaves.

Weeds compete with kale for water, light, and nutrients. Pull weeds as they appear and keep an eye out for pests like cabbage worms. I’ve plucked cabbage worms as late as November from my kale plants in my zone 5B garden. To discourage cabbage worms and other pests, place lightweight row covers or insect barrier fabrics overtop kale plants immediately after planting. The covers allow light, air, and water to pass through and can be left in place for months. Click here to learn more about imported cabbage worms and how to control them.

Can you grow kale in containers in winter?

Unless you’re in a mild climate it’s best to plant kale for winter harvests in the ground. My container grown kale plants die back by early January unless they’re wintered over inside my polytunnel. If you have a greenhouse, polytunnel, or other protective structure you can winter potted kale inside to extend the harvest.

How to protect kale plants in winter

You’ve got a choice of protective structures to use when growing kale in winter. My go-to season extenders are cold frames, mini hoop tunnels, and my 14 by 24 foot polytunnel. Below you’ll learn more about each type of structure and how to use them to enjoy a winter kale crop.

Cold frame – A cold frame is a bottomless box with a clear top used to create a microclimate around crops. It’s a handy structure in a home garden and can be used in spring, autumn, and winter to extend the harvest by weeks or months, depending on the crop. Kale is very cold hardy and we harvest all winter long from our polycarbonate and wood-framed cold frames. Cold frames typically have a low profile and I use them to grow compact varieties like dwarf blue curled scotch or baby kale.

Mini hoop tunnels – These are easy to DIY using lengths of 1/2 inch PVC conduit for hoops and clear polyethylene sheeting for the cover. This miniature greenhouse is ideal for protecting tall, mature kale plants like Winterbor or Redbor in winter. Discover just how versatile these structures are in my online course, How to Build & Use Mini Hoop Tunnels in the Vegetable Garden,

Polytunnel or greenhouse – Gardeners lucky enough to have a walk-in structure like a polytunnel or greenhouse can use it for growing kale in winter, as well as other cold-hardy vegetables like parsnips, Swiss chard, and Brussels sprouts. I typically have mature kale plants as well as baby kale in my tunnel for winter harvesting. I direct sow or transplant the seedlings during the growing season into the raised beds inside my tunnel. You can also grow winter kale in pots in a greenhouse or polytunnel.

How to harvest kale in winter

Baby kale is quick to go from seed to harvest and you can expect to start picking tender leaves just 5 weeks from planting. Full-sized kale plants need a few more weeks to grow, with most reaching maturity around 50 to 60 days from seeding. Harvest baby kale by pinching individual leaves from the plants. When I harvest kale from mature plants, I pick the oldest leaves first. These are the ones growing at the outside of the rosette. If you still have kale plants left in the garden by the time spring arrives, they’ll bolt. That means the plants switch from vegetative growth to flowering. You can harvest the broccoli-like flower buds to eat or let them bloom for the early bees.

Best types of kale for winter

When growing kale in winter, you’ll discover there are many types and varieties to try. They vary in their cold hardiness so gardeners in cold climates or those who wish to harvest all winter long should select the most cold tolerant varieties. Here are some of my favorite kales for the winter garden.

Darkibor kale

Darkibor is a deep blue-green kale with intensely curled foliage. The leaves are mild flavored and delicious raw or cooked. The mature plants grow up to 18 inches tall and form dense, attractive rosettes packed with the curly leaves. Plant Darkibor in a vegetable garden or in a landscape border for months of winter greens. This is a very cold tolerant variety.

Red Russian kale

This was the first kale I ever grew and I still grow it year-round in my vegetable garden. Red Russian produces vigorous plants with flat, grey-green leaves that are deeply toothed. The leaf stems and veins are deep purple-red and add welcome color to the veggie garden. This is one of my go-to varieties to grow for baby greens, but it’s also a standout when mature. It can tolerate temperatures down to 14 F (-10 C) when grown in a protective structure like a greenhouse or cold frame.

White Russian kale

White Russian Kale is similar in growth and appearance to Red Russian. The main difference is the leaves have white stems and veins. It’s ideal for baby leaf production or to produce full-sized plants, and is also tolerant of cold weather. Harvest from unheated structures down to 0 F (-18 C).

Winterbor kale

As its name suggests, Winterbor is a cold season superstar that is also vigorous and productive. The plants grow 2 feet tall and produce plenty of deeply ruffled blue-green leaves. This is one of my favorite winter kales for its extreme cold tolerance as well as mild flavor.

Redbor kale

Redbor is a spectacular kale with extremely curled leaves in an intense shade of purple-burgundy. The stem color matches the leaves making this a stunning choice for food or flower gardens. Redbor is similar to Winterbor in size and is also very cold hardy. The bold leaves of Redbor add welcome color to winter salads.

Dwarf Siberian kale

This compact variety grows 16 inches tall and wide and produces a heavy crop of large, lightly curled leaves. The plants are reliable and high-yielding and the leaves have a mild flavor whether harvested mature or as a baby green. Dwarf Siberian offers excellent cold tolerance.

Dwarf blue curled scotch kale

This heirloom kale grows only 14 to 16 inches tall but up to 30 inches across. The stocky plants form wide rosettes packed with leaves for winter soups, pastas, smoothies, or kale chips. The finely curled foliage is tender and mild-flavored, and cold hardy enough to persist all winter long under a season extender. I like to grow this compact variety in my cold frames.

Rainbow lacinato kale

This gorgeous kale, bred by Frank Morton, is the result of crossing Redbor with lacinato, which is also called dinosaur kale or Tuscan kale. The plants vary in appearance, but most have blue-green leaves tinted in purple. The stems and veins are also brilliant burgundy-purple. It’s more cold hardy than lacinato kale and adds bold late season color to the food or flower garden.

Can’t decide which kale varieties to grow? Pick up a bundle of kale seeds for a mixture of leaf textures and colours in your winter garden.

For more information on growing kale and other winter crops, be sure to check out these detailed articles: 

• Lacinato kale: learn how to grow this delicious heirloom vegetable
• How to grow kale indoors
• How to grow kale in gardens and containers
• 8 vegetables to grow in winter

Do you enjoy growing kale in winter?