The dusty miller plant (Senecio cineraria) does indeed look like it is covered with dust, but this look actually works for the plant. Rather than looking dirty and dingy, the small, shrubby plant presents a distinctive, silvery appearance that lends itself well to borders and contrasts nicely with colorful perennials and bedding plants.
Climate and Temperatures
Dusty miller grows best in warm, mild climates, but don't despair if you live in a cold area: Dusty miller can be grown as an annual or perennial. Dusty miller is a perennial evergreen -- relatively speaking -- in U.S. Department of Agriculture plant hardiness zones 7 through 10. It doesn't thrive in frost; although it can tolerate freezing temperatures, extended periods of frost will kill the foliage to the ground. Even so, in some cases, the plant will sprout again come spring. In climate zones lower than USDA zone 7, dusty miller is often grown as an annual plant because it is simple to grow and inexpensive.
Light, Soil and Water
For best growth, locate your dusty miller plant in full sunlight. It's a hardy little shrub -- it will still grow well in partial shade and even tolerates full shade, but the silvery hue will be reduced in the shade, and it will grow leggy. Plant it in moderately rich soil for best performance and keep it continually moist, but make sure the soil drains well because the plant can sometimes suffer from rust. Before planting, sprinkle an even amount of a slow-release fertilizer over the planting site and work it into the top 1- to 3-inches of soil. Repeat the application every four months. Dusty miller is not usually bothered by insect pests or diseases, and it will tolerate poor soil, heat, drought and deer, so go ahead and plant it where deer tend to roam.
Pinching and Pruning
Dusty miller does not produce flowers the first summer after planting, but if it lives to see another spring, it will bloom with cream or yellow flowers on tall, thin spikes. Many home gardeners think the flowers detract from the plant's showy foliage and clip them off. Pinching the flower buds as they appear encourages bushier growth. Dead foliage should be pruned off in late fall or during the winter, so long as it's done before new growth appears in the spring. Dip pruning tools in a mixture of 1 part bleach to 10 parts water to sterilize the blades and prevent the spread of fungi and bacteria.
Dusty miller makes an excellent container plant, but be sure any container housing a dusty miller plant has drainage holes in the base. Otherwise, the soil will not drain properly, and fungal disease may develop. In addition, use care when handling a dusty miller plant. The sap contains pyrrolizidine alkaloids, which can irritate the skin and eyes. Protect your hands with gloves, especially when pruning. The plant has low toxicity, but ingesting the leaves can cause liver damage, according to North Carolina State University.