Luckily for gardeners who live in colder climates, kale is one of the hardiest vegetables that can survive in temperatures that drop below 10 degrees Fahrenheit (minus 12 degrees Celsius). In fact, kale often tastes better once it’s been exposed to a couple of frosts.
However, it’s recommended that Kale only be grown in USDA zones 7 and above during the winter months. The lowest temperature in USDA zone 7 is 0 degrees Fahrenheit (minus 18 degrees Celsius). When growing kale in winter in zones 7 and above, you’ll be able to harvest this nutritional and versatile vegetable all throughout the colder months.
Let’s explore what you need to do to grow kale in winter.
When Should You Plant Your Kale?
If you want to harvest your kale during the winter months, you should start planting it around 3 months before the first frost is expected. This means that many gardeners will have to plant their kale in mid to late summer.
This can pose a problem for some areas because kale is not all that fond of hot weather. Therefore, if you live in an area that gets hot summers and cold winters, it might be a good idea to start your kale indoors or to plant the seeds into a pot and place this in a shaded spot in your garden.
You can then transplant your seedlings into the garden as the temperature starts to drop in the fall. Alternatively, if your summer temperatures never rise above 80 degrees Fahrenheit (27 degrees Celsius), you can plant your seeds straight into the garden. They’ll happily grow, and you can even start to harvest some of the small tender leaves to use in salads during the warmer days of summer.
The reason that you need to plant early is that kale will not put on a lot of growth during the colder months, so you want to ensure that your plants are a good size before the days start getting shorter.
In general, it takes around 50 to 60 days for kale plants to reach maturity, and this is the time when you can harvest a lot of the larger, outer leaves to add to your soups or to use for making kale chips.
How To Plant Kale For A Winter Harvest
When choosing the planting spot for your winter kale, choose a spot that gets plenty of sunlight, at least 6 hours a day. The soil should be well-draining and have plenty of organic matter added, as this will feed your kale during the warmer growing season.
You can start your kale either with seeds or transplants. For seed sown plants, sow the seeds around ½ inch (1.25 cm) deep and around 1 inch (2.5 cm) apart. This type of close planting allows you to harvest baby leaves during the warmer weather to use in your salads.
In order for the plants to grow larger, you want to thin out your seedlings once they’re about 3 to 4 inches (8 to 10 cm) tall so that there is around 12 inches (30 cm) space between each plant. You can use the leaves of the seedlings that you’ve pulled out in your salads or transplant the entire seedlings into another spot in the garden or into a large pot that you can bring indoors if the weather gets really cold.
If you don’t want to start your plants from seed, you can purchase seedlings or transplants from your local garden center. Make sure that you choose the most cold-tolerant varieties if your winters get quite cold.
Seedlings can be planted into the garden into well-draining soil that has been enriched with lots of organic matter. You can also plant some of the seedlings in the ground and reserve a couple for planting into a large pot or two.
This gives you the advantage of moving the potted kale indoors or into the greenhouse, if you have one, just in case you experience an unexpected deep freeze or a lot of snow.
When planting into the ground, space your seedlings around 12 inches (30 cm) apart to give them ample room to grow to maturity. If you’re going to be transplanting your seedlings in the middle of summer, make sure that the soil is nice and moist before you plant, and then water your seedlings to help to settle the soil around the roots.
Taking Care Of Your Kale Before Winter Arrives
Because you’ve planted your kale in the warmer months to achieve plenty of winter harvest, it’s important to look after it well before the cold weather arrives. If your area receives little rain during summer and fall, it’s important to keep your kale well-watered.
If you fail to give your plants the water that they need, the leaves will tend to be bitter and not as palatable. Therefore, ensure that your plants get all the moisture that they need and consider mulching the soil with hay or straw mulch to stop the moisture from evaporating from the soil.
If there’s no rainfall, plan to give your kale around one inch of water every week. To achieve this, you might have to water at least twice a week or when the top inch or two of soil is dry.
You also want to provide your young tender plants with some shade in the afternoon as they can get a little stressed in the heat. You can easily erect a shade structure that lets in the morning sun but keeps the plants shaded during the afternoon.
To promote optimum growth in your kale plants, you should fertilize them at least once a month during summer and early fall. Use a liquid fertilizer such as fish emulsion or liquid seaweed as this will encourage lots of leafy growth on your plants.
Make sure that you keep the area weed-free as well because weeds will compete with your kale for both moisture and nutrients. Another thing to keep an eye out for is cabbage worms. If left unchecked, these little pests can decimate your entire kale plants in no time.
One of the best ways to protect your kale from cabbage worms is by covering them with insect-proof netting. Just create a frame over your kale plants with some wooden stakes or some strong wire and drape the fabric or netting over the top. This will stop the cabbage white butterflies from laying their eggs in your precious kale plants.
Leave Your Kale Alone In Winter
In cold climates, there’s not much that you need to do to care for your kale plants. They won’t need to be watered, especially if the ground is frozen, and fertilizing would be a waste of time.
Therefore, the only thing that you need to do with kale during the winter is to just harvest the leaves as you need them.
The one thing you do want to watch out for is frost damage, and this will depend entirely on where you live. If you do notice that your plants are starting to show signs of damage, consider quickly creating a cold frame or a polytunnel to cover them.
What About If You Live In Zones Below USDA 7?
For those people who live in really cold zones, it’s still possible to grow kale through the winter, but you just have to do it differently. In other words, you want to protect your plants from extended deep freezes if you can.
One of the best ways to do this is with a cold frame. This is a structure that is just a bottomless wooden box with a hinged lid that is covered in glass or clear plastic. So the lid is just a wooden frame with clear plastic or glass covering the plants below.
This clever piece of equipment, which has been used by gardeners all around the world for centuries, protects the plants from frosts but still lets the sunlight in so that the plants can continue to grow.
Here are some tips for using a cold frame:
- You can place your cold frame on the ground and grow your kale in large pots if your frame is sitting on concrete or bricks. Otherwise, you can place your cold frame on top of the soil and plant your kale in the ground.
- Your cold frame should be facing south so that as much sun as possible can get through the lid to your plants.
- Plants within the frame won’t need a lot of extra water because there will be increased humidity within the frame.
- Other plants that benefit from growing in this cold frame include lettuce, cilantro, parsley, and rosemary.
As an alternative to using a cold frame, you can use a polytunnel or hoop house instead. These act in much the same way as a cold frame in that they protect the kale while still letting sunlight through during the cold days of winter.
To create a polytunnel, you just use plastic hoops to create the framework of the tunnel and then cover this with clear plastic polyethylene sheeting. Interestingly, you’re likely to find that the temperature within your polytunnel is around 10 degrees warmer than the air outside the tunnel.
If you don’t want to bother about building a cold frame or a polytunnel, you can just plant your kale in a pot and grow it indoors. However, you need to remember that your kale will need plenty of sunlight, so a south-facing window is ideal.
If your house is very dark during winter and not a lot of sun comes in, you can simply invest in a grow light and place your kale under this.
How To Harvest Your Kale In Winter
When harvesting kale in winter, it’s best to harvest only the oldest leaves first from around the outside of the plant. This will allow the inner leaves to continue to grow so that you can harvest them a little later.
Once spring arrives and the weather starts to warm up, you will find that your plants will bolt to complete their life cycle. When this happens, the leaves will become tough and bitter. However, you can harvest the flowers buds as these can also be eaten.
If you can, leave a few buds on the plants so the flowers can grow, as these will help to attract bees to your garden early in the growing season.
Best Varieties Of Kale To Grow For A Winter Harvest
If you want to grow and harvest kale right throughout the winter months, you want to select varieties that are the most cold tolerant. Here are a few to consider:
- Red Russian kale. This plant produces gray-green leaves that have toothed margins. The stems are deep red, and the leaves also have red veins.
- Darkibor kale. This is curly kale with blue-green leaves. It’s quite a tall grower and can reach a height of 18 inches (45 cm) tall. This is one of the best cold-tolerant varieties.
- Winterbor kale. Winterbor is another curly leaf kale that produces plenty of blue-green leaves. The leaves have quite a mild flavor, and the plant is very cold-tolerant.
- White Russian kale. This variety is similar to Red Russian kale, but it has white stems and veins instead of red ones.
- Redbor kale. The leaves on this pretty kale variety are very curly and have a deep burgundy coloring. This plant can add some much-needed color to a winter garden.
- Dwarf blue curled scotch kale. This compact variety is ideal for growing in large pots or under your cold frame. It produces wide rosettes with tightly packed leaves.
- Dwarf Siberian kale. This is a mild-flavored variety that produces masses of tender leaves that are lightly curled. It’s another very cold-tolerant variety.
- Lacinato kale. This variety is also commonly known as Tuscan kale. It has long blue-green leaves that are ideal for making kale chips.