How to Grow Kale Indoors and Outside for Delicious, Homegrown Superfoods

Some people love kale and some people don't, but everyone agrees on one point—it's unquestionably a superfood. This nutrient-packed member of the brassica family provides an impressive assortment of valuable vitamins and nutrients, including calcium, magnesium, potassium, and fiber—plus antioxidants!

Fortunately, you can grow this leafy green both indoors and in your garden. Here, we gathered some advice from experts to help you get started.

When to Plant

Kale is incredibly hardy, which makes it very easy to grow. Like most brassicas, it's a cool-season crop, so it doesn't perform well in the summer heat.

"Kale is one of my favorite things to grow here in the north precisely because of its cold hardiness," says master gardener Jennifer Rensenbrink. "You can plant it before the final frost in the spring, which usually means sometime in April here in Minneapolis."

She says kale also lasts well into the fall, and easily survives light frosts. "I've even harvested it frozen solid in December and used it for soup." 

How to Grow Indoors

Kale is typically grown outdoors, but it can be grown indoors in a container. You can start kale from seed indoors, or you can buy a transplant and place it in a container. 

1. If you're planning to grow kale indoors, horticulture educator Laura Irish-Hanson recommends choosing cultivars that were bred for growing in containers, or ones that are not too large at maturity, like Starbor.
2. If starting from seed, plant seeds 1/8 to 1/4 inch deep in the soil and lightly cover.
3. If using a transplant, plant it in your container so the top of the root ball is level with the top of the soil in your container.
4. "Kale will do best with lots of light," says Irish-Hanson. "So make sure you put the pot in the south-facing window or use supplemental light. Otherwise, the light coming through the windows is typically not very strong, and the plants will not grow well."
5. Irish-Hanson also recommends fertilizing container-grown kale regularly to encourage more leaf growth.
6. "Make sure you keep the soil moist, but not wet," she adds.

How to Grow Outside 

If you're growing directly outdoors, the steps are quite similar.

1. You can certainly grow kale from seeds if you'd like, or perhaps utilize transplants from a farmer's market or retailer. "If you start kale from seed, make sure you use a potting mix that is fine in texture, like a seed starting mix," says Irish-Hanson. 
2. Seeds should be just barely below the soil line—1/8 to 1/4 inches deep and lightly covered. "Because I plant it really early, I like to direct seed it, slightly thicker than what is indicated on the seed envelope," says Rensenbrink. "That way I can harvest whole baby kale plants as a way of thinning it out as it gets bigger."
3. Be sure to plant in full sun. "After the seeds germinate, and you see the seedlings emerge from the soil, make sure you provide direct light for 12 to 16 hours for the best seedling growth," says Irish-Hanson.
4. When transplanting seedlings, depth is important. "If you're potting up your seedlings or buying transplants to put in your garden or in containers, make sure you bury the plant to the same soil level," says Irish-Hanson. Place the transplants 18 inches apart.

Care Instructions

Success with kale requires the right combination of light, water, soil, and fertilizer. Here are some things to consider:

Sun

So many vegetables absolutely require full sun, and while kale does indeed perform its best in full sun, there's a bit of wiggle room to grow it in some shade. "It can grow fine with less sun; the growth is typically slower and the plants may be leggier," says Rensenbrink. 

Water and Soil

"Kale is a fairly adaptable plant," says Irish-Hanson. "It does best in well-drained soil, with medium moisture."

An inch or two of water per week is often plenty. You may want to plant your kale in soil that has been enriched with organic materials, because the plant requires a good amount of nitrogen to grow its fantastic leaves. 

Fertilizer

If your soil doesn't seem to be supplying your kale with everything it needs, then apply an occasional dose of a vegetable-specific liquid nitrogen fertilizer. "Fertilize regularly for continual leaf growth during the growing season," says Irish-Hanson. 

How to Harvest 

Harvesting kale couldn't be easier—it's much like harvesting lettuce. Often, you're looking to harvest older growth rather than newer, but not so old that it's fading or yellowing.

"Harvest kale by breaking leaves off, starting at the bottom of the stem, and working your way up," says Rensenbrink. "Never harvest more than one-third of the plant's total leaves at a time—that way it will stay healthy and growing."

Pests and Diseases 

Kale is typically a pretty hardy crop, but it can still fall prey to pests and diseases. Irish-Hanson notes that plants in the brassica family can be susceptible to attacks from various insect larvae.

"The most common ones are cabbage looper and imported cabbage worms," she says. "The caterpillars will eat the leaf blades in short order. Check for the worms on the underside of the leaves and on the stems of the plants."

She notes that kale can also be impacted by diseases like Alternaria, which causes black spots on the leaves. It's also susceptible to black rot, which creates yellow, triangle-shaped lesions on the leaf margins.

Common Mistakes

Like any vegetable, there are common errors that gardeners may run into when it comes to planting and growing.

One potential issue is incorrect spacing—just think about how large the kale will get later on. "If you want to have large plants that you can harvest from throughout the growing season and into the early winter, then make sure you give them enough space to grow," says Rensenbrink. "Follow the planting instructions from the seed packet or online to grow the best kale."

"Another mistake [people make] is not looking at all the different types of kale!" adds Irish-Hanson. "There are so many to choose from."