Growing Kale from Seed to Harvest

Kale is a frost-hardy cool-season dark leafy green in the brassica family. It’s high in vitamins, minerals and antioxidants; the easiest brassica for beginner veggie gardeners to grow and a versatile ingredient in the kitchen. Learn how to grow kale from seeds, transplant seedlings, care for kale plants over the growing season and harvest mature leaves.

Should you Start Kale from Seed or Transplants? 

The easiest way to get started growing kale is to buy seedlings from a local nursery, small farm, farmer’s market or big box store and transplant them into your garden. You might choose to grow kale from transplants if: 

• You’re a new gardener and don’t yet have the space or equipment to start seeds indoors.
• You’re just growing a few vegetables primarily for fun. 
• It’s not important to you what varieties of kale you grow.

On the other hand, there are advantages to growing kale from seed that you may want to consider before going with transplants. You may want to grow kale from seed if: 

• You want to be able to customize the varieties you grow in your vegetable garden or grow some fun and unusual varieties. 
• You want to extend your growing season by growing your cool season plants, like kale, in the “shoulders” of the traditional growing season - either in very early spring or fall - when growing conditions are ideal for cool season plants, but seedlings are hard to come by at garden centers. 

Kale plants only need to be grown indoors for 3-6 weeks before transplanting outside. Starting kale from seed is less of a time commitment for beginners than plants like tomatoes or peppers that need indoor care for 6-12 weeks. 

Should you Direct Sow Kale Seeds or Start them Indoors?

One way of planting kale seeds is to sow them directly in the ground as soon as your soil warms up in the spring. Direct sowing requires no seed starting supplies and seedlings that germinate outdoors don’t need the same level of care as those started inside. 

To direct sow, wait for soil temperatures to reliably reach 5C (40F), sprinkle your seeds over your garden beds, water the soil and keep the top of the soil moist until germination. As the seedlings come up, thin them to the appropriate spacing.

However, there are a few reasons direct sowing may not be as easy or foolproof a seed-starting method as it seems, especially when it comes to growing cool-season vegetables like kale.

Spring Kale

• Most seeds need warmer soil temperatures to germinate than the eventual seedlings will need to grow. Though kale plants can withstand frosts, kale seeds need a soil temperature of at least 4C (40F), but ideally much warmer, to germinate. As a result, direct sown kale may take a long time to germinate and only reach maturity late in the season. 
• Alternatively, if you start your kale seeds indoors you could be transplanting 6 week old kale seedlings into the ground at the same time as you would otherwise be sowing seeds and waiting for them to germinate. 
• This is a valuable head start if you have a short growing season, if you are really trying to maximize the amount of food you can grow in your space or if you just want to harvest some kale as early as possible.  
• ‍Seeds also need consistent moisture to germinate. When you direct sow you need to keep the top layer of your soil watered until germination, which usually takes 7-14 days but can take longer in cold weather. This can be challenging if your garden gets a lot of wind and it isn’t as convenient or comfortable as caring for seeds inside your house.

Fall & Winter Kale

• If you want to plant kale for fall and winter harvests, you need to start them about 3 months before your last frost date, which is often the hottest time of the year. Provided you have space available in your garden at this time, if you direct sow your kale in the middle of the summer, it may be too hot for your young seedlings to thrive.
• Starting your fall kale from seed indoors allows you to care for your seedlings in a controlled environment before transplanting them out when the weather begins to cool in late summer.

Supplies You'll Need for Growing Kale Seedlings Indoors from Seed

• Kale Seeds
• Seed-starting mix
• Cell trays or other containers
• Humidity domes or plastic wrap (optional)
• Labels or masking tape and a sharpie
• Grow Lights
• Oscillating fan (optional)
• Water-soluble fertilizer 

My seed starting guide contains all the basic information you need to get started growing your own vegetables, herbs and flowers from seed in more detail. 

How to Start Kale from Seed Indoors

1. Fill cell trays with pre-moistened seed starting mix (alternatively, prepare soil blocks.) Press the soil down or tap the tray on a flat surface. Fill the cells to the top with more seed starting mix. 
2. Drop 2-3 seeds onto the surface of each cell, press the seeds into the soil about ¼ inch deep, cover with a thin layer of soil and mist over the top of the cell trays with water. If you have it, sprinkle a layer of fine vermiculite over the soil. This helps with water retention and preventing green algae from forming on top of the soil. 
3. Label your seed trays with the variety name and date using labels or masking tape and sharpie.
4. Cover the tray with a humidity dome or plastic wrap to prevent the top of the soil and the seeds from drying out and set the tray aside to germinate. The tray does not need to be under grow lights at this time.
5. Kale seeds normally take about 1-2 weeks to germinate. Once germination begins, remove the humidity dome or plastic wrap and move the tray under grow lights positioned about 2 inches from the tops of the trays.

Caring for Kale Seedlings

Kale started from seed will need 4-6 weeks before it is an ideal size for transplanting into the ground. During that time, there are a few things you will need to do to care for them.

1. Keep the kale seedlings under grow lights for 14-16 hours a day. Having your lights on a timer is helpful. As the seedlings grow, adjust the lights so they remain about 2 inches above the seedlings. 
2. Keep the trays evenly watered but not soaking wet. Allow the tops of the trays to dry out before watering.  
3. Set an oscillating fan on low near the seedlings. This prevents the trays from staying wet for too long, and helps the seedlings develop strong stems. 
4. For the healthiest plants, once the seedlings have begun to develop their first set of true leaves, begin fertilizing them once per week with a diluted liquid fertilizer - I like to use this fish and seaweed fertilizer. 
5. If multiple seedlings have come up in each cell, thin to 1 seedling per cell or pull them apart and transfer each seedling you would like to keep to its own cell.

Planting Kale Seedlings in the Ground

1. ‍Get your timing right. Start your kale seeds about 4-8 weeks before your last frost date. The seedlings can be transplanted outdoors on or up to two weeks before your last frost date.‍
2. Harden off your seedlings. Since you’ve been taking care of your seedlings indoors for weeks in a comfortable environment, you will need to “harden them off” to prepare them for outside conditions. To do this, gradually bring your seedlings outside for incrementally longer periods of time over a week or two. Start by leaving them in shade or partial sun and work up to leaving them out in full sun. ‍
3. Choose your location: If possible, choose a full sun location - one that gets at least 6 hours of sun per day. Kale will tolerate part sun (3-6 hours of sun per day) but it will take longer to mature and may be best harvested as baby kale. ‍
4. Prepare your soil: Kale likes rich, well-draining, soil. I like to prepare my beds with a thick layer of compost and sprinkle a well-balanced organic granular fertilizer over the soil before planting.‍
5. Choose your spacing: Most sources recommend spacing kale seedlings 18-24” apart but you can get away with planting them much closer. I plant mine between 12-16 inches apart. But you do want to leave about 2’ between each row. ‍
6. Plant: dig a small hole with a trowel and pop the seedling into the ground, keeping the soil of the transplant level with the soil of the garden bed. Press the soil around the transplant firmly and water the seedling in. 

Basic Tips for Kale Plant Care

Watering & Fertilizing Kale Plants

• Like most vegetables, kale needs about 1 inch of water per week throughout the growing season. 
• If you have kale plants in your garden in very early spring or late fall, keep an eye on the weather and water them before a freeze. This will help them to survive the cold. 
• Kale does best in fertile well-drained soil. At the beginning of the growing season, top-dress or mix in plenty of compost into your garden beds where you will be planting Kale. You can also work a well-balanced granular fertilizer into the soil at the beginning of the season. 
• Kale may do well without any additional fertilization, but if your plants are slow-growing or pale green in color, you may want to side-dress with an additional application of compost, granular fertilizer or use a water-soluble fertilizer about 4 weeks after transplanting.

Protecting Kale from Extreme Temperatures

Kale is a hardy plant that prefers cool weather but can handle extremes. Many varieties survive hard frosts and are slower to bolt in hot weather than other brassicas.  

So while it isn’t necessary to baby your kale plants, there are things you can do to help them out in extreme weather that will extend your kale growing season as much as possible: 

• If you are transplanting your kale seedlings before your last frost date, consider providing them with protection from the wind and cold like frost cloth, a light row cover or a low tunnel. 
• If, on the other hand, warm weather is coming and your kale has yet to mature or you are still harvesting from it, you can protect it with shade cloth to prevent it from bolting before you get a chance to harvest.

Managing Pests & Disease

Compared to some other garden favorites like tomatoes or cucumbers, kale plants are relatively disease free. In over a decade of vegetable gardening I’ve never had a kale plant suffer from disease.

There are, however, a few kale-loving pests you may have to deal with. 

Cabbage Worms

The most common pest you are likely to encounter with kale are cabbage worms. These green worms are the larvae of white moths you may see flying around your kale and other brassicas in late spring. They lay eggs on brassica leaves which hatch into green worms that feed on the leaves. They leave unsightly holes but, if managed properly, shouldn’t threaten your kale harvest.

The best way that I have found to manage cabbage worms is to cover your brassicas with a light row-cover or insect netting in early spring when the cabbage moths are out looking for places to lay their eggs. 

Another option is to regularly monitor your kale and brassicas and crush any eggs you find on the leaves and hand-pick any cabbage worms, dropping them into a bucket of soapy water. 

Cabbage Aphids

A less common pest you may find in your kale are cabbage aphids. They are fuzzy and grey and congregate in large populations on kale leaves. They are most likely to be attracted to older plants that have been in the ground for at least a full season. 

They are incredibly unappetizing, difficult to remove, and will spread to nearby brassicas. If you find them on your kale, your best bet is to remove the plant entirely and dispose of it. 

Harvesting Kale

Kale can be harvested either by removing the entire plant or by using the cut-and-come-again method. 

Some of my favorite ways to use kale after harvesting are: sauteed with garlic and chili flakes, mixed through pasta dishes like this shrimp scampi or marry-me chicken pasta, or added to these crispy rice bowls with avocado.

Harvest the Whole Plant

Once your kale plants have grown to full size, you can remove the entire plant by digging it up or cutting it at ground level and leaving the roots to decompose underground. Then remove all of the leaves from the central stalk to be processed in the kitchen and toss the stalk into your compost. 

You might want to harvest your kale this way if you need the space for different vegetables or if the plants are old. Kale plants can be left in the ground from spring to fall and may even make it to the winter, but older plants are more susceptible to pests like aphids so you may want to remove them and start again with new seedlings. 

The Cut-and-Come-Again Method

Alternatively, you can use the cut and come again method to harvest your kale. 

Rather than pulling up each kale plant individually, when your kale leaves are mature, harvest from several kale plants at once, removing only the outermost and lowest, most mature, leaves from each plant. Make sure to leave enough leaves on the plant so it can continue to photosynthesize and grow.

Using this method, the kale will keep growing and you can continue to harvest from the same plants for 2-3 seasons.