How To Grow Kale In Greenhouse Successfully

You can get your fresh supply of the ultimate green superfood if you know how to grow kale in a greenhouse, which only includes four topics. Each step is easy to understand, and the indoor conditions the greenhouse provides makes how to growing kale in the greenhouse a question that you can quickly answer and teach to other gardeners. Once you get the general idea of kale’s indoor cultivation, you can try other kale square foot gardening methods. 

But why do more and more extensions and home gardeners are getting interested in growing kale in the greenhouse? Kale is more than just a trending smoothie ingredient. It’s one of the foods you can grow to fight infection, and the greenhouse makes the cultivation simple even for newbie gardeners. 

How To Grow Kale In Greenhouse Successfully

Definitive Guide On How To Grow Kale In Greenhouse

Knowing how to grow kale in the greenhouse means learning where and when to grow kale, the optimal temperature for kale, watering and feeding kale, and harvesting kale. These four topics are straightforward to learn, but consistency throughout the process of growing kale indoors is necessary to yield a good harvest. Once you get used to these pieces of information, you can start adding freshly harvested kale in your daily meals and improve your health. 


Where and when to grow kale

For kale, you want to choose an area in the greenhouse that will give the greens 6 hours of direct sunlight to ensure a good yield. The soil you’ll use should also have a pH of 6 to 7.5 and is rich in nitrogen, phosphorus, and potassium. Depending on which you think will be more convenient for your greenhouse, you can either use seeds or transplants for starting kale in the greenhouse. 

The Michigan State University recommends sowing kale seeds in mid-June to August, while you can start the transplants in March to July for planting out in April to August. The germination can take up to 10 days, and transplants can take six weeks to grow. For the spacing, allocate one square foot per plant, and it’s also possible to do companion planting with alliums and herbs.  


The optimal temperature for kale

The optimal temperature for growing kale is cooler than most crops, and it can even tolerate frost as long as the greenhouse doesn’t exceed 75°F. Mature kale plants are one of the hardiest crops, so if you’re in the growing zones 2 to 8, you should not face any problems growing kale. Cornell University even mentioned that being “kissed” by frost improves the flavor of kale. 

This tolerance to cold conditions is also one reason you should sow and transplant 4 to 5 weeks before the last frost date. Depending on your plants, some can tolerate 10°F and maintain their leaves without continuing to grow. And since you’re using a greenhouse, you don’t have to reach this point of extreme temperatures, so your kale will thrive year-round.  

Do note that while kale grows amidst cold conditions, high summer temperatures will be detrimental. Make sure to monitor the greenhouse temperature in the summer. Otherwise, you run the risk of low-quality crops with a bitter flavor and reduced growth. 


Watering and feeding kale

Like most greens, you must water your plants diligently during the growing season. The right measurement is giving one to one and a half-inch of water per week. An inch below the soil surface should be moist, so be careful not to overwater the plants. 

These water requirements will decrease after the first frost. What about feeding kale in the greenhouse? Feeding with balanced fertilizer should be enough once a month throughout the growing season. 

The University of Minnesota also recommends adding compost in spring or fall to improve soil quality. 


When to harvest kale

You can harvest kale when the leaves are as big as a hand. Assuming that you’ll harvest during frost, remember to take leaves from the base first because those touching the ground will not be useful later on. Ignore the torn or yellow leaves and pick a fistful per harvest. 

Since kale is grown annually, you must avoid picking the top center of your plant. Otherwise, the plant will stop producing. You can also extend your harvest because the plant continues to grow until 20°F.



Kale is probably one of the most popular green leafy vegetables. And if you’re interested in learning how to grow kale in a greenhouse, you’ll be pleased that this crop is relatively easy to cultivate, mostly indoors where you have control over the conditions. Remember to study where and when to grow kale, what’s the optimal temperature for kale, watering and feeding kale, and when to harvest kale. 

These four areas should help you ensure a good and quality yield. Remember the kale requirements from soil quality and spacing, location, feeding and watering, and optimal temperatures. Since it is a frost-hardy crop, you shouldn’t face any drawbacks, even if you live in a cold region. 

Still, maintain the optimal temperatures for kale in the greenhouse to keep it growing and productive. While it is a biennial, most gardeners in all USDA plant hardiness zones grow kale as annuals. Overall, you should be the one planning your growing season that will be suitable for your area. 


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