Can Cosmos Flowers Grow in Rocky Soil?

Getting To Know Cosmos

• The common cosmos and the orange cosmos plants are native to Mexico, South America and the southwestern United States. Both can be found growing wild in these areas, and in places where cosmos has naturalized beyond flower gardens, blooming throughout the summer months until frost. Both are annuals, but often reseed, and if grouped in large numbers may return for the next season. Common cosmos has showy, single daisy-like flowers growing on erect stems with medium green leaves that appear threadlike. Flowers come in rose, pink or white with yellow centers. Orange cosmos has orange or yellow single flowers and long, narrow leaves with hairy margins. These low-maintenance, warm-weather-loving cosmos grow from 2 to 4 feet tall.

Growing Cosmos

• Your cosmos will grow well in rocky soil, as long as it is well-drained. Common and Orange varieties of cosmos require planting in full sun. Sow seeds in early spring or after danger of frost has passed for early to mid-summer bloom, and in mid-summer for late summer bloom. Plant your seed by scattering, then raking it into the soil about 1/16 inch deep. Keep your soil moist for 5 to 10 days after seeding. The seeds should germinate between 7 to 21 days. Once plants emerge, water sparingly because these cosmos provide more blooms with less water than most other annuals. Cut your plants back after blooming to about 12 to 18 inches high to encourage re-bloom. Both cosmos grow well in U.S. Department of Agriculture plant hardiness zones 2 through 11.

The Importance Of A Little Neglect

• Too much water, fertilizer and shade will produce long, leggy plants. Giving your cosmos full sun, watering only when they begin to wilt and providing little or no fertilizer can produce better growth. Some gardeners may think the common cosmos are more delicate than the orange variety but according to Texas A&M's Aggie horticulture website, they both thrive on "tough love."

Companion Plants For Cosmos In Rocky Soil

• The blanket flower (Gaillardia pulchella) is another plant happy to grow in your rocky soil as long as it is well-drained. It prefers full sun to part sun, little water and does not need rich, fertile soil. Most Gaillardia are perennial, but the blanket flower is an annual. It is easy to grow from seed, and tolerates heat and drought. Flowers come with a red center and yellow tips, and are 1 to 2 inches across. The plant grows from 12 to 24 inch tall with clumps of hairy leaves. Flowers may be seen in solid orange or yellow on occasion. The blanket flower enjoys growing in USDA zones 3 through 11. The French marigold (Tagetes tenuifolia) is a perfect choice for a garden with rocky soil, good drainage and hot, dry conditions. It seeds easily and needs only occasional watering and no fertilizer. This hardy plant's blooms may be orange, yellow, golden or bicolor. According to the University of Florida IFAS extension, this French marigold will grow in all USDA hardiness zones.