Matthiola incana, also known as common stock or gillie flower, performs as a cool weather annual or biennial. Hardy in U.S. Department of Agriculture hardiness zones 7 through 10, the flowers may return for a second year of blooms in warmer climates. In most areas of the United States, however, Matthiola incana flowers do not survive the heat of summer. Gardeners prize common stock for its ease of care, early bloom time and clusters of aromatic blossoms that appear in spring. The flowers are often harvested for use in floral arrangements and decorative displays.
Choose a planting site for the Matthiola incana flowers that receives full sun to light shade and consists of moist, fertile, well-draining soil. Prepare the area by tilling to a depth of at least 6 inches with a garden tiller and incorporating a 2- to 3-inch layer of organic compost into the soil prior to planting.
Plant Matthiola incana seeds in the garden after the danger of frost has passed and temperatures reach 10 to 12.8 degrees Celsius. Sow the seeds no more than 1/2-inch deep, as they need light to germinate, and space them 12 to 18 inches apart to allow room for the full mature size of the plants.
Water your Matthiola incana flowers about once a week, or frequently enough to maintain consistently moist soil. Do not allow the soil to dry completely or wilting may occur. In addition, do not allow standing water to accumulate, as the flowers are prone to developing root rot.
Apply a 1- to 2-inch layer of organic mulch to the soil surrounding your Matthiola incana flowers to promote the soil's moisture conservation and protect the roots against the summer heat. Leaves, grass clippings, bark chips and straw are all suitable mulches.
Feed your Matthiola incana flowers with an all-purpose garden fertiliser just after planting to stimulate new growth and help the plants establish themselves in the garden. Follow the fertiliser manufacturer's instructions on the label for proper dosage and application.
You can start Matthiola incana flowers indoors about 6 to 8 weeks before the last frost date, if desired. Sow the seeds 1/2-inch deep and 1 inch apart in a sterile seed starting mix. Place the seeds in an area that receives indirect light and keep the growing mix moist. Transplant seedlings outside after the threat of frost is over and temperatures reach 50 to 55 degrees Fahrenheit. In most climates, Matthiola incana flowers begin to decline in early summer when temperatures rise to above 26.7 degrees Celsius. The plants will not return the next year unless you sow more seeds in the spring. If you plan on harvesting Matthiola incana flowers for display, pick them when half of the flowers on the spike have opened. Place the flowers in a tall vase and remove any leaves below the water line.