Growth Facts for Purple Basil

Purple Basil Cultivars

• Purple basil is the same species as the common, green-leafed sweet basil. To get a purple variety, look for cultivars like "Dark Opal," "Rubin," "African Blue," "Purple Ruffles" and "Purpurascens." The "Purpurascens" cultivar is believed to be the original purple basil cultivar that was used to create the array of new varieties. Basil plants, including purple basil varieties, belong to the Lamiaceae plant family.

Propagation

• Purple basil seeds take one to two weeks to germinate at 70 degrees Fahrenheit. Plant purple basil seeds 1/4 inch deep in a prepared garden bed, or in peat pots or seed flats indoors. To overwinter basil, take 4-inch-long cuttings in late summer. Slip the bottom one-third of the cuttings into a glass jar with water. When roots develop, transplant the cuttings into a container with potting soil. Purple basil cuttings develop roots in two to three weeks.

Growing Temperatures

• Basil needs heat for proper growth. Plant purple basil outdoors in the spring when nighttime temperatures are regularly above 50 degrees. Basil can survive down to 45 degrees, but the plants will be stunted for the first part of the growing season. If temperatures drop down to freezing, purple basil tends to turn black and rot. Clip off dead leaves if a light, late-season frost damages the leaves, but if the whole plant turns black, replace it after the last frost has passed.

Growing Requirements

• Grow basil in full sun -- they should get at least six hours per day or more, if possible -- and space plants 10 to 12 inches apart. Purple basil grows best in sandy, loamy soil with good drainage and a pH of 5.5 to 7.5. You can also grow basil in 10-inch-diameter pots or larger with a standard potting soil. Keep basil growing vigorously by watering it every seven to 10 days, allowing the soil to dry slightly between waterings. Soak the soil around each plant until it is damp at least 12 inches deep. Water basil in containers when the soil feels dry 1 inch deep.

Fertilizer and Pest Management

• Good growth requires the right nutrients. Fertilize basil in the spring after planting, and again in the summer using a 5-10-5 granular fertilizer. Use 3 ounces of fertilizer for each 10 feet of garden bed by sprinkling the fertilizer around the base of each plant. Fertilize basil in containers using 1/4 teaspoon of liquid all-purpose plant food dissolved in 6 cups of water every three to four weeks. Basil is mostly pest and disease free, but the Japanese beetle can do some damage. Pick off Japanese beetles by hand to prevent them from damaging the leaves.