Kale is an excellent leafy green vegetable to grow indoors. Fast-growing and cold-tolerant kale will grow indoors year-round if you follow a few simple steps.
If you are a regular reader, you know I grow a lot of kale. Why? We like the taste, and kale is versatile and can be used in many ways, including salads, stews, soups, healthy smoothies, and more.
Follow my simple steps, and you will be a master kale grower in no time. All it takes is a bit of time and attention to detail.
- Choosing the right seed starting trays and containers
- The ideal no-fuss growing medium
- Providing Adequate Lighting
- 1. Watering and soil moisture
- 2. Providing sufficient light
- 3. Controlling the temperature
- 4. Nutrients and Fertilization
- 5. Managing Pests and Diseases
- Fresh tender leaves in salads and stir-fries
- More mature kale leaves in soups, stews, and smoothies
- Frozen leaves in soups, smoothies, and stews
It starts by selecting a suitable kale variety
Not all kales are the same. And when growing indoors, you need to consider space and available light. Below I list three of my favorites. But there are many more kale varieties to choose from.
- Germination time: 5-15 days
- Time to mature plant: 50-70 days
- Temperature: Geminate seeds at approx 20 degrees Celsius / 68 degrees Fahrenheit and move to a cooler spot after sprouting
1. Curly Kale
The “Dwarf Green Curled” is my favorite curly kale variety and is easily recognized by the tightly curled and often bright green leaves. Curly kale will grow 75 cm / 30 inches tall, but the dwarf varieties grow to about 50 cm / 20 inches. Harvest early for tender leaves or grow until maturity for that winter green flavor.
2. Nero di Toscana
Nero di Toscana is another favorite and is also known as Tuscan kale and produces dark blue-green, slightly wrinkled leaves with a bright central nerve. Nero di Toscana is cold-resistant and can grow 75 cm / 30 inches tall but can be harvested earlier for more tender leaves.
3. Red Russian Kale
Red Russian kale adds interest to any indoor garden with its green leaves and almost purple stalks and nerves. Slightly smaller variety at 65 cm / 25 inches, but again, early harvest is recommended as young leaves are tender and will spruce up any fresh salad.
Whichever variety you choose, this guide will help you grow and harvest healthy and tasty kale leaves. The golden rule is to start seeds in warm soil (20 degrees Celsius / 68 degrees Fahrenheit) and then move the plants to a cooler growing environment after they sprout.
Using a heat mat makes it easy to control germination temperature, but from my experience, it is not a must.
Getting ready to grow kale indoors
Growing kale indoors is relatively easy; still, it pays to be prepared. Here we will look at selecting suitable seed starting trays and containers and the optimal growing medium and discuss how to provide sufficient lighting year-round.
Choosing the right seed starting trays and containers
Seed starting stage: Deep seed starting trays work best as they allow roots to grow deep.
Seedling stage: Potting into nursery pots saves space and makes soil moisture control easier.
Plant stage: You can use any container if you ensure proper draining and sufficient depth.
Drainage holes help prevent excess water from collecting in the pot and causing root rot.
Ideally, choose pots at least 15-20 cm / 6-8 inches deep for proper root development. Suitable container materials include:
- Plastic containers
- Ceramic pots
- Terracotta pots
- Fabric grow bags
Each container must sit on a plate or saucer to collect water runoff.
Tip: Select containers that are easy to move, to make it easier to adjust the location throughout the growing process.
The ideal no-fuss growing medium
- Seed starting: Use a proper quality potting mix. For kale, soil-based potting mixes are my preferred choice, but soilless mixes will also work. You want a well-draining potting mix with excellent moisture retention and aeration.
- Kale seedlings: Pot up your kale seedlings into a nursery pot when your kale plant sprouts its second pair of true leaves.
- Kale plants: When you see roots growing through the drainage holes at the bottom of your nursery pot, you are ready for your final pot up.
For each pot up, you need to introduce more fertile potting soil. Most soil-based potting mixes include soil amendments like coco coir, Perlite, or vermiculite, organic matter like compost, and slow-release fertilizers.
You can, of course, mix your own potting mix. The key is to use a mix that provides the necessary nutrients while maintaining a balance between potting mix aeration, drainage, and water retention. Most commercial potting mixes deliver this balance to help your kale plants to stay healthy and thrive.
I have said it before, and it is worth repeating. It all starts with the soil. Do not use regular garden soil, as it will be too compact, and you risk introducing pathogens that could harm your indoor plants.
Providing Adequate Lighting
All plants need sunlight to grow and thrive. Kale plants need at least 6-8 hours of natural sunlight daily.
Place your kale plants near a sunny windowsill or use full-spectrum grow lights if natural sunlight is limited.
You must double the light you give your plants when using full-spectrum grow lights. Set a timer on a cycle of 18 hours on and 6 hours off for an optimum growing environment for your kale plants.
The good news is that full-spectrum grow lights do not have to be expensive. There are good options for any budget, and the grow lights will last a long time.
Another advantage of full-spectrum grow lights is that they give light without producing significant heat. And as kale is a cooler-temperature plant, grow lights allow you to provide sufficient light while keeping the temperature inside the ideal range of 15-20 degrees Celsius / 60-68 degrees Fahrenheit.
Planting Your Kale Seeds
Sowing Kale Seeds
Starting kale from seed is as easy as 1-2-3. You only need kale seeds, a seed starting tray, and a quality potting mix.
Fill the seed starting tray with a pre-moistened potting mix. Apply gentle pressure to each cell. This will compact the soil slightly and create space for your seeds.
You want the potting mix to be moist, not wet. You should be able to make a “soil ball” in your hand. The ball should hold its shape but crumble when you press it with your fingers.
Next, place 2-3 kale seeds in each cell and cover them with about 1 cm / 0,5 inches of potting mix.
Finally, gently mist each cell using a spray bottle, cover the tray, and place it in a warm spot.
Germination and Sprouting
Your kale seeds need warmth and moisture to germinate. But watch out for condensation forming ironside your cover.
I aim for a soil temperature of approx 20 degrees Celsius / 68 degrees Fahrenheit, and seeds germinate in 5-15 days. Sometimes quicker but rarely later than 15 days.
If your potting mix dries out, mist using a spray bottle.
When the first leaves sprout, remove the cover and place the seeding tray under a full spectrum grow light or another location with plenty of sunlight.
A window sill will work, but be mindful of the temperature. It is often safer to place the seed tray away from the window to benefit from the sunlight but not to get the full effect of the heat.
Keep the potting mix moist and, if possible, keep a consistent moisture level in the growing medium.
Pot up your kale seedlings into nursery pots when they have developed at least two pairs of true leaves or reached a height of about 7 cm / 3 inches.
You can skip the nursery pot step and pot up straight to a larger container. I prefer the nursery pot step, as a smaller pot with less soil makes it easier to control soil moisture.
When you see roots growing from the bottom of the nursery pots, pot up the kale seedlings to their final and larger container.
When growing kale indoors, the leaves are often harvested before reaching full maturity. Harvesting early yields crisper and more tender leaves that are great in salads.
Do not plant your kale seedling too close together. When planting outdoors, kale should be given 50 cm / 20 inches of space between plants. Indoors I plant one kale seedling in each pot and maintain space between the plants for airflow and circulation.
Caring for kale plants
Looking after your kale plants is not complicated. It is more about being aware of the growing environment and trying to create the best possible growing environment, given your available space.
I have divided this part into five areas:
- Watering and soil moisture
- Providing sufficient light
- Controlling the temperature
- Nutrients and fertilizers
- Managing pests and diseases
1. Watering and soil moisture
For vigorous, healthy plants, try to maintain consistent soil moisture.
Do not let your plants dry out, and I recommend bottom watering your plants at least once per week, depending on the time of year.
If you prefer top watering, water thoroughly and seldom, rather than a little every day. If you are unsure, a soil moisture meter is an inexpensive tool to help you create better watering habits.
Another helpful technique is to water by weight. Lift the pot before you water it and create a mental note of the weight.
Next, bottom water the plant and let it absorb all the water it can retain. After letting the pot run off excess water, pick it up again and create a new mental note of the weight.
These mental notes will help you understand how dry the soil is below the surface layer.
Same-size pots do not necessarily dry out at the same time. Check each pot individually.
2. Providing sufficient light
Plants need light to develop and thrive. Kale needs 6-8 hours of natural sunlight per day. Double the number of hours if you use full-spectrum grow lights. I recommend setting a timer on a cycle of 18 hours on and 6 hours off.
3. Controlling the temperature
Kale prefers a growing environment on the cooler side of the scale. Aim for a temperature range between 15-20 degrees Celsius / 60-68 degrees Fahrenheit.
A cooler temperature is fine but avoid higher temperatures.
4. Nutrients and Fertilization
Giving your kale plants nutrients and fertilizer starts with using a fertile, well-draining, nutrient-rich potting soil that contains a mix of compost, vermiculite, and perlite.
But this will not be enough if you want your plants to thrive.
Kale is fast-growing and needs nutrients and fertilizers to grow. Use a nitrogen-heavy liquid fertilizer or to keep it simple, use a well-balanced fertilizer (NPK 10-10-10).
I add fertilizer when I move the plant to its final larger container and then 2-3 times more before harvest.
If the leaves start looking pale, it is time to add nutrients.
5. Managing Pests and Diseases
I cover all varieties of kale when growing outdoors. Indoors is, however, a different story.
When you grow kale indoors, you are less exposed to many pests and diseases commonplace outdoors.
Still, pests and diseases are a factor in indoor gardening. Inspect your plants daily and look for leafhoppers, aphids, cabbage worms, and harlequin bugs to mention a few possible suspects.
As I have written many times, prevention, early detection, and manual removal should always be your first line of defense.
If you detect an infestation too late, consider using a Neem oil water solution or a mixture of water, baking soda, dishwasher detergent, and vegetable oil.
If your plants suffer from fungal diseases, spray the leaves with a Neem oil solution or a mixture of water, baking soda, dishwasher detergent, and vegetable oil. Always treat plants early morning or evening to avoid exposing the treated leaves to direct sun.
To prevent fungal diseases, always water the plants from the bottom to avoid getting the leaves wet and ensure spacing between plants for proper airflow and circulation.
Healthy plants are more resistant to disease. Pests and diseases are consequently more frequent in stressed plants. One of the most effective ways to protect your plants is to maintain healthy growing conditions with good watering habits, proper temperature control, and sufficient nutrients.
When to Harvest Kale
Kale can be harvested as sprouts and all the way to mature leaves after a 50-70 day growing period. There is no right or wrong.
I prefer to harvest younger, tender leaves and typically start harvesting the out leaves after 20-30 days. I never let my indoor kale plants reach full maturity.
How to harvest kale
Harvesting kale is all about the leaves, not the whole plant.
I follow three simple rules:
- Harvesting the right leaves: Harvest the oldest and lowest leaves on the plant first to allow new leaves to continue growing from the center.
- Use clean precision garden scissors: Harvest the leaves using precision garden scissors, and do not harm the central stem or new growth.
- Harvest regularly: Harvest kale leaves whenever you can. You decide if they are large enough. Regular harvesting promotes new growth and keeps the plant healthy.
Using and Storing Your Kale
We use kale in 3 different ways.
- Fresh tender leaves in salads and stir-frys
- More mature kale leaves in soups, stews, and smoothies
- Frozen leaves in soups, smoothies, and stews
Fresh tender leaves in salads and stir-fries
Fresh, tender kale leaves can usually be harvested after about 20 days. And these tender leaves are excellent in salads and stir-fries.
Harvest the leaves from the outer sides of the plant and wash them to remove any dirt or debris.
Another favorite is to chop the leaves into bite-sized pieces and sauté them with garlic, olive oil, and a pinch of salt.
More mature kale leaves in soups, stews, and smoothies
More mature leaves can be added to stews and soups and are a great addition to give your smoothies a nutritious boost.
Rinse the leaves and use them fresh or blache them first in lightly salted water if you prefer.
Frozen leaves in soups, smoothies, and stews
We freeze kale in portion-sized pucks for later use. These frozen portion-sized kale pucks are ideal for adding to any hot meal for an added nutritional boost and flavor.
Froze kale loses its texture and is less suited for salads and stir-fries.
Storing your kale harvest
If you are lucky enough to harvest more than you can consume, there are several ways to store your harvest.
We keep kale in the refrigerator and freeze some of our kale harvests. You can also dry or dehydrate kale. We have tried it, but we prefer freezing.
Proper storage is essential to prolong the freshness of your kale.
Store kale in the refrigerator: Place the unwashed kale in a plastic bag with a sheet of paper towel and cut a few holes for air circulation. Place in the crisper drawer of your refrigerator, and the leaves will keep fresh for up to a week.
Freezing kale: To freeze kale, wash, blanch, and dry the leaves before placing them in a freezer-safe bag. Squeeze out the air and seal, then store in your freezer for several months.
Related article: Follow the exact same step as listed in the article: How to store and preserve chard
Drying kale: Use a dehydrator or place the kale leaves in a single layer in a preheated oven (50 degrees Celsius / 122 degrees Fahrenheit) – but leave the oven door ajar. Check back every couple of minutes to avoid leaves burning and crumbling. Store the dried leaves in a cool and dark place.