How to Grow Zwolsche Krul

Add water to the seed tray to moisten the soil thoroughly about eight weeks before the last frost. Use the tip of your finger to make a 1/4-inch-deep indentation in the center of each cell. Sprinkle three or four Zwolsche Krul seeds into each indentation and cover them with 1/4 inch of soil.

Set the tray in a cool, sunny spot indoors and keep the soil moist as the Zwolsche Krul seedlings sprout. After six weeks, place the Zwolsche Krul outside for three hours a day to acclimate them to the outdoors. Ensure the temperature is above 50 degrees Fahrenheit when the seedlings are outside. At the end of the eight weeks, pluck away the weak seedlings from each cell, leaving only the thick-stemmed, leafy ones.

Select an outdoor area that maintains a steady temperature between 60 and 70 degrees Fahrenheit and receives sunlight for no more than half the day. Spread a 2- to 3-inch layer of compost over the area you intend to grow the Zwolsche Krul. If you are using a container, lay the compost over a quality potting soil. Use a gardening trowel to mix the compost into the soil.

Take a reading from the area with a soil pH testing kit per manufacturer's instructions. Zwolsche Krul grows best in soil between 6.0 and 6.5 pH. To increase the pH, mix in wood ash, and to lower it, mix in sulfur. Start with no more than a handful, repeat the test and continue adding small amounts until the soil tests between 6.0 and 6.5 pH.

Separate the cells of the seed tray and dig holes for each one in your prepared planting area, about 12 inches apart. Wait to do this until low temperatures are consistently above 50 degrees Fahrenheit. Place the cells into the prepared holes and gently press the existing soil around them. Water the area thoroughly with a mixture of water and liquid fertilizer according to the manufacturer's instructions.

Water the Zwolsche Krul's soil to keep it moist, and use the mixture of water and liquid fertilizer every four to six weeks. In 100 to 120 days, the Zwolsche Krul will be ready to harvest. About 10 days before harvest, blanch the stalks by placing straw around them, covering everything but the curly leaves at the top. This protects them from sunlight and enhances their flavor.

Pull up the entire plant and cut off the roots to harvest the Zwolsche Krul. Alternatively, after about 80 days you can cut off the leafy tops, which will grow back once more for a second harvest. This detracts from the stalk's flavor, but yields larger amounts of leaves.