Silver ragwort (Jacobaea maritima) is a very white-wooly, heat and drought tolerant evergreen subshrub native to the Mediterranean region. This species was formerly known as Senecio cineraria. Some species of bees build nests on silver ragwort’s leaves. This species is deer resistant and often cultivated for horticultural purposes.
I. Appearance and Characteristics
Jacobaea maritima, commonly known as silver ragwort, is a perennial plant species in the genus Jacobaea in the family Asteraceae, native to the Mediterranean region. It was formerly placed in the genus Senecio, and is still widely referred to as Senecio cineraria; see the list of synonyms (right) for other names.
Silver Ragwort is a very white-wooly, heat and drought tolerant evergreen subshrub growing to 0.5–1 m (1.6–3.3 ft) tall. The stems are stiff and woody at the base, densely branched, and covered in long, matted grey-white to white hairs. The leaves are pinnate or pinnatifid, 5–15 centimeters (2.0–5.9 in) long and 3–7 centimeters (1.2–2.8 in) broad, stiff, with oblong and obtuse segments, and like the stems, covered with long, thinly to thickly matted with gray-white to white hairs; the lower leaves are petiolate and more deeply lobed, the upper leaves sessile and less lobed.
The tomentum is thickest on the underside of the leaves, and can become worn off on the upper side, leaving the top surface glabrous with age. The flowers are yellow, daisy-like in dense capitulo 12–15 millimeters (0.47–0.59 in) in diameter, with central disc florets surrounded by a ring of 10–13 ray florets, and enclosed in a common whorl of bracts at the base of the capitulum. The seeds are cylindrical achenes.
Jacobaea maritima is widely used in horticulture for its silvery foliage. It is winter-hardy in USDA Zones 8-10, tolerating winter temperatures down to -12° to -15 °C, tolerant of light shade but preferring full sun. In colder areas it is grown as an annual plant. Many cultivars have been selected for particularly dense silvery tomentum, such as ‘Cirrus’, ‘New Look’, ‘Ramparts’, ‘Silverdust’, ‘Silver Filigree’, and ‘White Diamond’. It has been recommended in North America for its fire resistance, resistance to browsing by deer, and its salt tolerance.
The cultivar ‘Silver Dust’ has gained the Royal Horticultural Society’s Award of Garden Merit.
Confusion in the horticultural trade exists between J. maritima and Centaurea cineraria, which has resulted in confusion regarding which cultivars pertain to either species, which has also resulted in much confusion in photographs of these species on the internet.
Dusty miller is toxic to pets and can be toxic to humans as well when eaten.
II. How to Grow and Care
Sunlight
Dusty miller does best in full sun but will tolerate part shade. In more shade, the silver look of the leaves will be less intense, and the plants will look more green.
Climate and Temperature
You can grow this pretty plant during the warmer months in any climate. In cold climates, cooler than USDA hardiness zone 7, they typically won’t survive the winter.
To increase the odds of your plants surviving the winter when the temperatures drop below zero, mulch your flower beds well to help protect the roots. Plants may be more prone to foliage diseases in very wet, humid climates.
Watering
Once established, Silver ragwort is a drought-tolerant plant. If planted in the garden, it rarely needs additional watering as it tends to get its needed moisture through regular rainfall. Young plants that haven’t been established yet need regular watering until they form a strong root system.
Soil
Dusty miller plants adapt to various soils, but good drainage is key for healthy plants. Whether your soil is on the rocky side or is characterized by clay, you can improve your pH (it prefers a range of 5.5 to 6.0) and drainage by amending it with compost.
Fertilizing
Silver ragwort is not a heavy feeder and it thrives best in poor soil. Applying a layer of manure or garden compost in the spring will probably be just fine. If your soil shows a nutrient deficiency, you may apply a fertilizer to fix the issue.
Planting Instructions
If growing dusty miller from seed, start them indoors about ten weeks before your area’s last frost in spring. Sow the seeds in a location with 65º-75ºF temperatures where there’s lots of light, uncovered on top of moist potting mix. Within 10-15 days, germination will take place.
If transplanting from containers, make a hole the same size as the container and add the plant so the stem is at the same soil level it was in its pot. Fill in around the root ball with soil and water well. Add more soil if needed.
Pruning
Dusty miller doesn’t need pruning, but if some of the leaves begin to yellow or if it starts to sprout small flowers, you can clip them off for a more appealing look.
Overall, dusty miller doesn’t mind being pinched or sheared back. This will actually help promote new growth and keep the plants lush and bushy. You can cut them back to promote a flush of new silver growth late in the season, when plants often start looking scraggly and leggy.
Propagation
This species is very easy to propagate and grow. Start plants from seed in the spring or start new plants from cuttings taken from mature plants.
Seed
Are you ready to grow dusty miller from seed? It’s quite simple to do. Start seeds indoors 8 to 10 weeks before your average last spring frost date. Do not bury the seeds. Simply sprinkle them on the soil surface and press them onto the soil to make full contact. Then, water the soil well and keep the soil warm and moist until the seeds sprout, possibly up to three weeks after sowing.
If you use multi-cell pots and have sown multiple seeds per cell, thin them to one seedling per unit. Keep the seedlings warm and the soil moist, and keep them in a location with plenty of bright sunlight or under a grow light. After all the danger of frost has passed and your seedlings are several inches tall, you can safely transplant them into your garden or planter.
Seedlings
Sometimes, it’s just easier to buy seedlings from the store. In the spring, many garden centers selling summer bedding plants will have them in stock.
You will probably have a variety of multi-cell pots full of perky little plants to select from. Choose a healthy-looking batch. Check to see that the stems are straight and strong.
The leaves and stems should be firm and vibrant looking. Don’t buy plants with obvious signs of rot or insect damage.
Cuttings
If you can access a mature plant, you can take cuttings to create more plants. Cut a healthy section of stem tip three or four inches long.
Remove the lower couple of leaves to have a bare stem on one end and a few healthy leaves at the tip end. Dip the bare stem in rooting hormone and then plant the stem in fresh, clean potting soil.
Keep your cutting in a warm, brightly lit location, and keep the soil moist to the touch. After a few weeks, you should start to see fresh leaves growing, and this will be your sign that the cutting was successful.
Potting and Repotting
Like in garden beds, dusty miller’s silvery tones add a lot to container gardens and hanging planters. Use a light, porous potting mix in a container with plenty of drainage. If winters are cold, bring potted dusty miller plants indoors to protect them from the cold.
Overwintering
Dusty miller is tolerant of cold weather within its hardiness range, but you can reduce watering in the late summer to ready it for winter. Prune it back with sharp, sterile shears to just above ground level and mulch with pine needles or straw.
Pests and Diseases
This plant is generally not bothered by many pests or diseases. Avoid wet soil conditions that can lead to root rot and fungal diseases like rust. As with any plant, watch for potential insect invasions, such as aphids.
- Root Rot
If plants sit in wet, saturated soil, they can develop root rot. You will notice something is wrong with your plant because it will start to look limp and mushy.
The leaves and stems will become soft and brown, and plants will fall over. Once a plant has developed root rot, it may be best to remove it and avoid overly wet conditions. However, you can try rejuvenating the plant by carefully removing it from its soil, pruning off damaged roots, and replanting it in a fresh, well-draining potting mix.
- Rust
This plant is somewhat prone to rust. Rust is caused by a fungal infection that is most common after an extended period of wet weather. Rust on dusty miller generally looks like yellow or orange patches on the undersides of the leaves and, if allowed to spread, will infect the entire plant, causing it to appear stunted, deformed, or die.
If you have had problems with rust, try to choose disease-resistant varieties. At the end of the growing season, remove leafy debris from around the plants where diseases can overwinter and spread the following year. Water your plants from below rather than unnecessarily spraying water on the leaves.
- Aphids
Aphids are small, soft-bodied insects, typically green, pink, or grayish in color. They suck hide on the undersides of leaves and along stems, sucking plant juices with tiny piercing mouthparts. Aphids will cause stunted growth and deformed leaves, and they can transmit plant diseases.
To help control aphids, encourage beneficial insects to visit your garden. Spray heavily infected plants with a jet of water to dislodge and disrupt the aphid feeding cycle.
Spray infected plants with insecticidal soap, but do this in the evenings to minimize potential harmful contact with beneficial insects that fly primarily during the day. Closely follow the directions on whichever product you decide to use.
III. Companion Plants for Dusty Miller
Dusty miller’s felted, silvery leaves are a perfect combo with colorful, long-blooming trailing stems of petunias or million bells. Also, purple and silver is another color mix that pleases the eye, so think about snapdragons, lavender, or pansies as another suitable companion for dusty miller. It also makes a handsome companion plant for other sun lovers like zinnias, pentas, or salvia.
Ornamental grasses look attractive with dusty miller, providing a different texture to the garden. In contrast, basil mixed with dusty miller brings pollinators, might keep other bugs away, and gives your garden a pleasant scent.
IV. Uses and Benefits
Plant dusty miller in your garden to add silvery brightness amid colorful flowers or lots of greenery. Plant in an area that gets full sun most of the day but with some shade later in the afternoon in very hot climates. Use it as a background for low-growing annuals, as an edging plant, or in containers. This low-maintenance plant will thrive in drought-tolerant gardens.
V. Types of Dusty Miller
The difference between dusty miller cultivars can be seen in how dissected the foliage is. Some varieties are lacy and delicate, while others are slightly lobed.
- ‘Cirrus’: Broad leaves with scalloping on the edges adorn this variety.
- ‘Silverado’: The fern-like foliage is famous in many gardens.
- ‘Silver Lace’: This variety has very fine foliage, as the name implies.
