To grow kale indoors, place the plant in an area with plenty of sun and temperatures that remain under 80 degrees Fahrenheit throughout the year. Kale is a hardy plant that grows well in container gardens.
Germinate kale in a loamy soil that contains compost and a natural fertilizer, such as fish emulsion, and maintain a temperature of 70 to 80 degrees Fahrenheit until the seeds have sprouted. Add limestone as needed to maintain a pH of around 5.5 to 6. Place the plants in a sunny window during the winter months and in an area with afternoon sunshine during the warmest months of the year. Very hot temperatures, such as those found in a greenhouse, can result in bitter kale leaves, while kale grown in cool temperatures is milder in flavor.
Opt for clay pots to ensure the soil remains moist, and water only as needed when the top layer of the soil becomes dry. Kale is typically harvested in cold weather, or when the leaves are about the size of a hand. Harvest only the outer leaves of the plant to allow the center to continue producing edible leaves, and cut one or two kale leaves from each plant with sharp scissors to harvest kale without damaging the plant. Allow the plants to go through at least two hard frosts by placing containers outdoors or in a cold room. After exposure to cold temperatures, the leaves release their natural sugars and become sweeter.