Several plants share the name dusty miller. The two most common are Senecio cineraria and Centaurea cineraria. Both have silver grey, velvety foliage and are popular as accent plants and for bed edging. Both dusty millers are drought-tolerant and can be used in hot, dry climates. Centaurea does escape gardens in California but has not naturalised.
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Descriptions and Bloom Time
The two species have similar requirements. Centaurea cineraria is a woolly Italian perennial herb from the aster family. Senecio cineraria is a perennial native of the Mediterranean from the aster family with velvet silvery foliage. Centaurea cineraria forms arching mounds 18 to 24 inches high and wide. Senecio cineraria has a looser form with pyramidal clumps of about the same height. Although grown for their foliage, dusty miller plants do bloom. Senecio cineraria blooms in its second year during summer, so gardeners planting it as an annual rarely see the flowers. Flower heads form as yellow four-inch clusters. Centaurea cineraria produces leggy blue flower clusters in the first year.
Climate and Soil Requirements
Both dusty millers are Mediterranean-climate plants. In places such as southern California, dusty miller grows nearly year-round. It does not do well in rainy environments and dies back in frost. In cold climates, you find it offered as a summer annual. Dusty miller is recommended for USDA Hardiness Zones 8 through 10. Well-drained soil is a must for both dusty millers. Both will grow in sandy soils. Centaurea cineraria is more adaptive and grows on alkaline, salty and clay soils.
Planting and Propagating
Dusty miller plants are most commonly acquired from nurseries. Either species likes planting in full sun, though Senecio cineraria tolerates some shade. Centaurea cineraria is cold-tolerant and can be planted before your first frost-free date. Space the plants of either species six to 12 inches apart. Water regularly till established. You can start dusty miller seed indoors and set the seedlings out to harden off after the last frost date in spring. When planting seeds outdoors, leave Senecio cineraria seed uncovered. Dusty miller will root from cuttings taken from semi-hard growth tips. Summer is the best time to take cuttings.
Both dusty millers are drought-tolerant and require light watering. They should only need extra water during extremely hot, dry periods. Both species are well suited for xeriscaping.
Hot, humid climates or overwatering will cause a disease called rust. Dusty miller also suffers from root and stem rot if overwatered. All parts of Senecio cineraria are extremely poisonous if eaten, so gardeners should be careful of kids and pets around the plant.
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