Description & Interesting Facts:

Jacobaea maritima is commonly known as Silver Ragwort or Dusty Miller.  It was formerly placed in the genus Senecio, and is still widely referred to today as Senecio cineraria. It is a small perennial plant in the genus Jacobaea, in the family Asteraceae.  The genus has around 35 species of flowering biennial or perennial herbaceous plants, and many forms with distinctly different leaf shapes are available to gardeners, although all have that familiar silver-grey look about them.

It is native to the western and central Mediterranean region, in northwest Africa (Morocco, northern Algeria, Tunisia), southern Europe (Spain, Gibraltar, southern France including Corsica, Italy including Sardinia and Sicily, Malta, Slovenia, Croatia, Bosnia and Herzegovina, Kosovo, Albania, Montenegro, Serbia, Macedonia, and Greece), and the far west of Asia (Turkey). It occurs primarily on cliffs and rocky coastal sites, and more rarely inland.

It is naturalised further north in Europe, and in Great Britain and Ireland, where it also occurs mainly in mild coastal areas, and also in North America.

Jacobaea maritima 'Silver Dust'

The cultivar 'Silver Dust' has gained the Royal Horticultural Society's Award of Garden Merit. It is best known for its feathery, silvery-grey to almost white foliage that is exquisitely soft and fuzzy to the touch, rather than its loose clusters of yellow daisy-like flower heads which may appear on long stems in the plants second year of growth, in summer.

The flowers are not particularly ornamental, and some cultivars do not flower at all. Many gardeners prefer to remove the flowers as they can detract from the foliage. Seeds are produced in cylindrical achenes.

In cold winter regions the dusty miller is generally planted as a fast growing summer annual and is often sold in seedling trays. In one season it will generally grow around 15 to 30cm tall with an equal to slightly wider spread. However, in milder climates where it is grown as an evergreen perennial, mature plants can reach 60cm tall with an even wider spread.

Jacobaea maritima Picture by Carl Lewis from flickrIn the Garden:

Every award winning flower garden relies on the shapes and colours of surrounding plants to act as a foil for its blooms, and dusty miller certainly fits the bill beautifully. With its silvery-white foliage it stands out as a neutral coloured plant that can be used in almost any colour scheme.

Dusty Miller is the ultimate team player and a great complimentary plant for other flowering annuals in sunny sites, so use it as an accent plant in containers, as an edging plant, or in borders and mixed plantings.

It is a stunning contrast for plants with darker foliage and flowers that bloom in shades of cool purple and blue, violet, pink, and magenta. It also pairs well with hot red and orange flowers. Even white flowers benefit from the glow of dusty miller's textured leaves.

White flowers and silvery-white and grey foliage are essential in “moon gardens” as they stand out in the moonlight, making dusty miller a firm favourite to plant around outdoor entertainment areas.

In North America it has been recommended for its fire resistance and its salt tolerance in coastal gardens.

Cultivation:

Where does dusty miller grow best?

Because the dusty miller is of Mediterranean origins where it is both heat and drought tolerant, going dormant during the dry season, it thrives in our winter rainfall regions.

Does dusty miller tolerate humidity?

Excessive humidity isn't a problem if the plants have adequate spacing with good air flow around the foliage, and a position in full sun.

Is dusty miller cold and frost hardy?

Dusty miller is moderately cold tolerant, but because its super-fast growing, in very cold and frosty gardens it’s usually treated as a summer annual.

It will last past the first frost, but the leaves die back when temperatures are consistently below freezing. If the crowns are mulched in autumn, to prevent them from freezing, vigorous new growth will emerge again in late spring.

Is dusty miller drought tolerant?

The fuzzy growth that gives dusty miller its sheen also helps it tolerate periods of drought. Like other plants that hail from Mediterranean climates, dusty miller can get by with occasional watering once it is established.

In Mediterranean climates it is considered a water-wise garden plant because it handles very dry and hot summers by going dormant until the autumn rains arrive.

In the garden it will look at its best if watered regularly, but guard against overwatering as it does not like soggy conditions.

How much sun does dusty miller require?

The plant does best in full sun but will tolerate some shade, however the colour of the leaves is more intense in full sun, and in too much shade the plant will become ‘leggy’.

What soil type does dusty miller prefer?

Dusty miller plants adapt to various soils, but good drainage is the key for healthy plants. In the wild it thrives on sandy or rocky soils, and prefers moderately acidic soils with a pH range of 5.5 to 6.0, but will adapt to most garden soils which drain well.

Does dusty miller require fertilising?

Dusty miller plants are light feeders, and in reasonably fertile soils mulching annually with compost, well-rotted manure or leaf mould will be sufficient. In very poor and impoverished soils the plants will respond well to mulching together with a balanced fertiliser.

Does dusty miller require pruning?

Dusty miller plants require no pruning to maintain their pleasing bushy shape. However, they are not without their faults, and if grown as an evergreen perennial, they regularly seem to hollow out underneath as old leaves shed, signalling that it’s time for a hefty cut.  You can cut them back hard in spring or summer and they will shoot back immediately.

The loose, yellow flower heads are not very ornamental and many gardeners opt to nip the buds out.

Propagation:

Most people purchase dusty miller as bedding plants but they can also be grown from seed or cuttings.

Sow seeds directly into well prepared garden beds after the last spring frost, sowing at a depth of 6mm. Germination is quick, and within two to three weeks you will have little seedlings. Thin the seedling out to space them 10cm apart, and a final thinning to space them about 15 to 20cm apart.

Take tip cuttings in spring or semi-hard wood cuttings in summer. Cut off a 10 to 15cm piece of stem with clean, sharp shears. Strip the leaves from the base and dip the stem in rooting hormone. Fill a small pot with soilless potting soil like palm peat and insert the stem into the medium. Keep it moist and warm until new leaves grow, then transplant as desired.

Problems, Pests & Diseases:

If grown correctly dusty miller suffers from no serious insects, diseases, and other plant problems, making it perfect for busy gardeners who don’t wish to spray.

Slugs enjoy snacking on dusty miller plants, especially in flowerbeds that receive frequent irrigation. Hand-pick the pests, or use beer traps to control their numbers.

Excessive watering can cause root rot. This is more of a problem in clay soils. In areas with heavy soil, you can prevent it by growing your dusty miller plants in containers or raised beds.

The plants may be susceptible to rust.

Is dusty miller toxic?

Although primarily known as being toxic to horses and cattle, dusty miller is also listed as being toxic to humans, dogs and cats.

Always supervise young children in the garden and discourage pets from chewing on plants.