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Allium caesium

Allium caesium
Blue onion, Persian blue allium, Ornamental Onion

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This botanical ornamental garlic blooms in May-June at 35 to 60cm (14 to 24in) from the ground. It bears spherical umbels measuring 10cm (4in) in diameter, composed of small sky-blue flowers with a darker midline, the whole taking on a more greyish tone at maturity. Its habit is remarkable in natural beds, but also in bouquets. Grow it in light, well-drained soil that is dry in summer. It prefers a very sunny exposure.
Flower size
10 cm
Height at maturity
50 cm
Spread at maturity
20 cm
Exposure
Sun
Hardiness
Hardy down to -18°C
Soil moisture
Dry soil, Moist soil
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Best planting time October to November
Recommended planting time January to March, September to November
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Flowering time May to June
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Description

Allium caesium is a superb ornamental plant with blue flowers that blooms in the wild in dry meadows and desert regions of Central Asia to Siberia. In late spring, this beautiful botanical species forms large spherical umbels of varying blue shades, turning grey over time. It is highly popular with butterflies. Fabulous in contemporary or natural-inspired compositions with valerian, thistles, and grasses, this bulbous plant thrives in well-draining and light soils, even when dry in summer. Its flowers are magnificent in dry or fresh bouquets. 

 

Allium caesium belongs to the Amaryllidaceae family, just like leeks, onions, and garlic in our vegetable gardens. It is a hardy botanical species (-15°C (5°F)), and is relatively easy to grow in any well-drained soil that does not retain too much moisture. Its inflorescences resemble those of A. caeruleum, but they are larger. The vegetation emerges from the ground in spring, and the floral stems reach an average height of 45cm (18in). This plant spreads on the ground by multiplying bulbs. Flowering takes place in May-June, in the form of 10cm (4in) diameter umbels. Each umbel is composed of small star-shaped flowers with 6 petals. They are sky-blue with a white base and a central indigo blue vein. There are indigo blue anthers in the centre of these small flowers. Very durable, the umbels mature to a lavender-grey colour in the garden and in vases. After fertilisation by pollinating insects, they produce capsules that remain decorative for a long time. The foliage consists of long, simple, basal, linear leaves with parallel veins. The leaves disappear shortly after flowering. The plant survives summer and winter in the form of bulbs. 

Plant Allium caesium in a contemporary or rustic flower bed, especially in a dry garden. It will express its full potential in large groups of at least 10 to 15 bulbs. Plant it with white, mauve, pink, or red valerian, Verbena 'Buenos Aires', and shrubby wormwood. Alternatively, use it as a border plant behind a row of boxwood balls or germander that are well pruned. It can also be planted along a wall or pathway, or in isolated clumps in the midst of creeping bugle, ensuring a decorative effect. It works well in beautiful pots. It can be used in bouquets: to reduce the alliaceous scent of the flowers, you can add a drop of bleach to the vase water or change the water regularly.

 

Plant habit

Height at maturity 50 cm
Spread at maturity 20 cm
Growth rate normal

Flowering

Flower colour blue
Flowering time May to June
Inflorescence Umbel
Flower size 10 cm
Fragrance slightly scented
Good for cut flowers Cut flower blooms

Foliage

Foliage persistence Deciduous
Foliage colour medium green

Botanical data

Genus

Allium

Species

caesium

Family

Alliaceae - Liliaceae

Other common names

Blue onion, Persian blue allium, Ornamental Onion

Origin

Central Asia

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Planting and care

Alliums are easy-to-grow plants in light soils that do not retain excessive moisture. Plant them preferably before the end of October so that they have time to establish themselves properly. They dislike moisture and waterlogged soils in winter or summer. Give them a sunny spot in well-drained, rocky or sandy soil. Plant them 10 or 15cm (4 or 6in) deep, spaced 15cm (6in) apart. They are undemanding but do prefer poor soils. It is important not to cut the foliage before it has completely yellowed, to allow the bulbs to replenish their reserves. Once acclimatised and established, this allium is resistant to summer drought. If growing conditions are met, this bulbous plant requires no maintenance, but does not like root competition from other perennials. Alliums are robust plants and not prone to diseases if the conditions are right. They multiply slowly by producing bulb offsets, eventually forming beautiful clumps.

Planting period

Best planting time October to November
Recommended planting time January to March, September to November
Planting depth 10 cm

Intended location

Suitable for Meadow, Rockery
Type of use Border, Edge of border, Container, Slope
Hardiness Hardy down to -18°C (USDA zone 7a) Show map
Ease of cultivation Amateur
Planting density 10 per m2
Exposure Sun
Soil pH Neutral, Any
Soil moisture Dry soil, Moist soil, well-drained, lightweight

Care

Pruning No pruning necessary
Soil moisture Dry soil, Moist soil
Disease resistance Good
Overwinter Can be left in the ground

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