Velvet centaurea (Centaurea cineraria) is an evergreen perennial that will grow from 15 to 61 cm tall. Thrives in full sun to partial shade. Blooms in summer with white or yellow flowers. Grown for its gray-green foliage, which contrasts beautifully with darker green plants in the garden. Oftentimes, flowers are trimmed away to encourage thicker leaf growth.
I. Appearance and Characteristics
Centaurea cineraria, the velvet centaurea, also known as dusty miller and silver dust (though these latter two names may also apply to Jacobaea maritima and Silene coronaria), is a species of flowering plant in the family Asteraceae endemic to southern Italy. In natural settings, it grows on coastal cliffs, ranging from 0–350 m above sea level, hence the plant’s Italian name, fiordaliso delle scogliere (lit. “cliff cornflower”). Mature plants may reach 80 centimetres (31.5 in) in height. The species produces purple flowers.
Centaurea cineraria is taxonomically complicated, with several described subspecies and significant geographic variation. Members of the C. cineraria group have variously been treated as full species, as subspecies, or simply as regional variations.
Centaurea cineraria is commonly cultivated for its foliage. Depending on climate, it can be grown as either an annual or as a perennial. In cultivation, this species prefers full sun and well-drained soil.
Because of similar leaf shape, leaf hairiness, and leaf color, there has been much confusion in the horticultural world between C. cineraria and the unrelated Jacobaea maritima (with Senecio cineraria being an old name for Jacobaea maritima). Jacobaea maritima has similar foliage to C. cineraria (indeed, “cineraria” means “ash-gray colored”). Cultivars like ‘Silver Dust’, ‘Silver Lace’, and ‘Cirrus’ are sometimes mistakenly referred to as C. cineraria but these cultivars actually pertain to J. maritima.
The cultivar ‘Colchester White’ (named for the leaf color, not the flower color) does actually pertain to C. cineraria and is the most common cultivar of this species. This confusion has also resulted in many images on the internet being mistakenly identified, resulting in identification of cultivated material challenging, especially without reproductive parts.
II. How to Grow and Care
Sunlight
Velvet centaurea requires long periods of sunlight for proper development. Although, it should not be under direct sunlight during the hot summer days, when the sunlight is very intense, as the plant might start wilting and developing burns. It is best to keep it in a partial shade.
Sunlight requirements for velvet centaurea sometimes cannot be met during winter, when the days are shorter. Exposing the plants to artificial light during the night will effectively extend light exposure and provide them with enough light to get through the winter. This practice also encourages early flowering.
Temperature
Velvet centaurea is mainly grown in the Mediterranean region and Southwest Asia. It is cold-resistant and dislikes intense heat, but nevertheless enjoys warm climates. Optimal conditions for growing them include a relatively dry environment and temperatures between 15 to 25 ℃. It is adapted to grow in hardiness zones 3-8.
Velvet centaurea is tolerant to drought and shouldn’t be planted in soils that are prone to hold water. If it is planted in the garden it can grow on its own, absorbing rainwater after its roots are fully developed. But be careful – an excess of water will cause the stem to become weak and fall over. Another danger of excess moisture includes the development of root rot, which can be detrimental to velvet centaurea.
Watering
Velvet centaurea needs moderate amounts of water for proper growth, so the watering should be done once every 3-4 days during the spring and fall. When temperature in summer is high, large amounts of water evaporate, so watering should be done twice a day – in the morning and in the evening. However, to avoid accumulation of water in the soil, the plant can also be sprayed with water. During the winter, velvet centaurea should be watered once in every 1-2 weeks, as it is better to keep the soil slightly dry.
Soil
Velvet centaurea is adapted to various soil types. It can grow in both heavy clay and rapid draining sand. However, for the most favorable growing conditions, it is best to use fertile, loose and well-drained sandy soils. A mix of garden soil, a bit of sand and wood ash is the best potting substrate.
In order to prevent pests and diseases from occurring (or recurring), velvet centaurea should not be planted on the same plot for many consecutive years; when it comes to potted plants, substrate should be replaced annually.
Fertilizing
Velvet centaurea is tolerant to infertile soils, but adequate nutrition will promote blossom. Before sowing, generally an appropriate base fertilizer is applied (preferably an organic or mineral fertilizer) during soil preparation. Nitrogen-based fertilizers can be applied during vegetative phase to promote growth.
Half a month before bloom time, fertilizers based on phosphorus and potassium (e.g. monopotassium phosphate) can be applied to promote flowering. Try to avoid excessive fertilization, because otherwise, it will only benefit the growth of weeds, resulting in an overgrowth of plants but reduce flowering.
Planting Instructions
The Root system of velvet centaurea has one main root, making it suitable for direct sowing. Sowing should be performed in spring and fall. Sowing in spring needs to be carried out as early as possible. The suitable temperature for germination is 15 to 20 ℃, and the seedling will emerge after 4-7 days.
Before sowing, mix the seeds and fine sand in a ratio of 1:2-3, and sow them evenly. Comb the plot gently with a rake afterwards. After sowing, the covering soil should not be too thick, as it is advised to cover the seeds tightly, otherwise the seedlings might grow unevenly.
Crush the soil with a tool to combine the seeds with the soil tightly. Finally, cover it with a non-woven fabric or a straw curtain to increase ground temperature and promote seed germination. It is best to choose a windless day for sowing. The sowing height should be reduced if the wind is strong.
Pruning
Velvet centaurea grows side branches naturally, and too many of them will cause the flowers to grow smaller. Producing larger flowers can be achieved by cutting off some terminal buds. During the mid-summer, climate conditions are usually unfavorable for growth of velvet centaurea, and the leaves start to wither and turn light green or yellow. At this point, the plant can be cut off to a third or to half of its height. When the weather becomes cool, it will rejuvenate and grow new leaves and flowers.
During winter it is advised to cut off the roots of velvet centaurea that have perennial roots below the ground, to ensure that the plant survives cold temperatures and frosts.
Propagation
Velvet centaurea is mainly propagated by sowing and division. Its seeds are scattered easily, so it’s best to harvest them in batches, when the inflorescences turn yellowish-brown after the petals have fallen. The seeds should be sown in spring or fall.
If the sowing is performed in fall, it needs to be at a place protected from low temperatures, or planted indoors in a seedling tray and then transplanted in spring. It has strong viability and can self-propagate. The seeds successfully germinate on their own with enough water.
Perennial species can also be propagated by division. Division includes digging out a cluster of plants 2-3 years old, and separating them with a sharp knife, each cluster preferably containing 3-5 small buds. Individual clusters serve as new planting material. Division is generally carried out during spring or fall. The soil must be kept moist before the new roots have properly grown.
III. Harvesting and Storage
You can harvest the flowering branch of velvet centaurea. It can be done when the petals on the outer circle of the inflorescence are fully expanded. Use sharp garden shears to harvest them when the temperature is low in the morning. Put them in a vase with clean water in time to avoid water loss.
