A. Verbena bonariensis and Verbena rigida are tender perennials, and are often grown in Canada as annuals, as they prefer warm, dry climates. Seeds may be started indoors 8 to 10 weeks before planting out, or outdoors after the last frost. The seeds should just be covered lightly with soil. Germination is usually 14 to 90 days. Requirements prior to seeding are darkness and a temperature of 65 to 75 degrees Fahrenheit. The seeds should be placed in a plastic bag, together with a moist growing medium and refrigerated for two weeks, then sown.
After the last frost, when nighttime temperatures remain above 50 degrees Fahrenheit, the plants may be transplanted to the outdoors in full sun; light shade if summers are very hot. Verbena require well-drained, fertile soil, around 6.0 to 7.0 pH. Verbenas can withstand drought, but will reward you if you water regularly. Pinch out tips of young plants and deadhead frequently to ensure maximum blooming. Verbenas bloom from summer to frost.
To propagate, you may take cuttings in spring, or in early autumn to overwinter indoors, or grow from seed (as described above). Verbena bonariensis will bloom from seed in its first year and generously self-seeds .
Master Gardeners of Ontario