<em>Amsonia</em>, blue bluestar: planting and care

Description and botany

Amsonia is a semi-shrubby perennial of the family Apocynacées, like periwinkles, oleander and Mandevillas. It originates mainly from meadows, wooded and sandy areas and cool edges in United States, and occasionally from Greece and Turkey.

Genus includes 22 species of perennials and bushes including Amsonia tabernaemontana, the broad-leaved amsonia also called “blue amsonia” or “blue star” and its cultivars and hybrids (Amsonia tabernaemontana Var. Salicifolia, Amsonia ‘Blue Ice’) which are most commonly grown in gardens. Amsonia ciliata, the ciliate amsonia with feathery foliage or its more compact subspecies Amsonia ciliata filifera, Amsonia hubrichtii and oriental amsonia (Amsonia orientalis) are also attractive species for gardens.

From a more or less lignified stump, these herbaceous perennials form over time handsome, bushy clumps, erect yet very supple, which can reach 1 m depending on species. Amsonia can take a little time to establish in garden, taking about 2 to 5 years after planting to flower well, but once well rooted it shows great longevity.

Plant stands out for its abundant foliage, both light and graceful, which varies with species. Stems exude a milky sap when broken and bear deciduous leaves that are more or less narrow. They are alternate, ovate to lanceolate, with a central vein and 5 to 10 cm long. Amsonia hubrichtii is distinguished by very fine, needle-like leaves, Amsonia orientalis bears willow-like leaves while Amsonia ciliata produces very fine leaves edged on the lamina with numerous hairs when juvenile.

Amsonia tabernaemontana

Bright green, slightly yellow-green to dark green, this foliage takes on beautiful autumn colours in most Amsonias, turning golden yellow, orange or bronzy gold before dropping.

From May to September depending on climate, flowers emerge abundantly and are clearly visible above this elegant, sometimes feathery, foliage, which remains attractive outside flowering period. They are grouped in pyramidal panicles borne at tips of erect stems. Flower buds bristling with white hairs open into small, tubular star-shaped flowers 2 to 3 cm across. Corolla comprises five narrow, pointed petals fused into an elongated tube and set within a villous calyx.

These erect flower stems display whole range of blues, from very pale lilac-blue, through sky blue to deepest steel blue (Amsonia ‘Blue Ice’).

Highly melliferous, they attract butterflies, bees and other pollinating insects throughout summer. Their flowers are lovely in fresh, delicate summer bouquets.

After flowering, Amsonia produces small dehiscent pods containing decorative winged seeds.

Very hardy down to -15°C, Amsonia grows in all gardens, in sun that is not scorching or in partial shade in soil that stays cool during warm season. It is a must-have in wild and naturalistic gardens, easy to place in a perennial bed or mixed-border, where it will bring lightness and country charm alongside other summer-flowering perennials.

Main species and varieties

Most popular

Our favourites

Amsonia tabernaemontana var. salicifolia

This hybrid bears looser clusters of flowers than the typical form. Its leaves are elongated and resemble those of willow.

• Flowering time July, August
• Height at maturity 80 cm

See the product sheet

Amsonia Blue Ice

A magnificent hybrid distinguished by a more compact habit, larger flowers and a more intense blue than other Amsonia. Perfect for adding charm to borders and beds.

• Flowering time June to August
• Height at maturity 35 cm

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Amsonia ciliata

This species is notable for feathery, pilous foliage that takes beautiful autumn colours. Ideal for adding lightness to beds when planted in drifts.

• Flowering time July
• Height at maturity 75 cm

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Amsonia hubrichtii

We love its very abundant steel-blue flowering rising above thread-like leaves shaped like needles that turn golden-yellow to orange. Its dense foliage sets off neighbouring plants.

• Flowering time June to August
• Height at maturity 80 cm

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Amsonia ciliata Ernst Pagels

A fine hybrid with light foliage that takes lovely yellow tones in autumn. Perfect in a perennial bed with a natural habit.

• Flowering time July, August
• Height at maturity 1 m

See the product sheet

Amsonia orientalis

Its leaves resemble those of willow. Over time it forms large bushy clumps.

• Flowering time August to October
• Height at maturity 1 m

See the product sheet

Planting

Where to plant Amsonia?

Very hardy to -25°C, Amsonia adapts easily to all gardens, one of the perennials most resistant to cold! It will probably struggle more in Mediterranean climate, too dry and hot in summer. Its only requirement is soil that does not dry out in summer.

If it tolerates any good garden soil that stays cool, including calcareous or even sandy soils, it will perform better in a loamy, rich, well-drained and fairly light soil.

It can withstand summer heat and drought if soil remains slightly moist and cool. In winter, however, its roots will not tolerate excess water that could encourage fungal diseases.

It prefers non-scorching sun or light shade. It needs a few hours of sunlight per day for optimal flowering.

It is a vigorous perennial, well suited to planting in informal meadow-style beds, or to lighten flowering in mixed borders, provided soil never dries out in summer. It will also find its place at woodland edge, beneath deciduous trees that will provide welcome shade.

Border of Amsonia tabernaemontana var. salicifolia

When to plant?

Plant Amsonia in your garden preferably between February and April, or in autumn from September to November.

How to plant?

Planting in small groups creates a lovely effect in beds; plant amsonias in groups of 3 to 6 buckets per m², spaced about 30 to 50 cm according to size at ripeness. This perennial will decline in soil that is too wet in winter: in heavy or clay soil, add gravel or coarse sand to improve drainage.

• Soak rootball in a bucket before planting
• Spade soil well to loosen it
• Dig a hole 2 to 3 times larger than the rootball
• Spread gravel or clay pebbles at bottom of hole
• Optionally enrich soil with some compost
• Place rootball and backfill without burying the collar
• Firm soil lightly then water thoroughly
• Mulch to keep soil cool
• Water regularly during first weeks to encourage establishment

More advice on how to plant a perennial on our blog!

Care and maintenance

Hardy and vigorous, Amsonia will prove faithful and generous provided soil remains cool and it is left undisturbed!

Mulch the base from May with a good layer of organic mulch to keep soil cool at the roots and water regularly during the first weeks and the first summer after planting to prevent soil from drying out. Afterwards water mainly during prolonged hot spells. As it ages it will become more resistant to drought. Let the plant establish itself without further disturbance and avoid soils that are too wet in winter.

A simple tidy-up of the clump is sufficient: cut back the clump in late winter, between February and March. In winter, the plant dies back completely: mark its position if necessary.

Amsonia is a robust perennial that is free from disease.

Propagation: sowing, cutting, division

Amsonia multiplies very easily by division of clumps in spring or early autumn, by sowing under cover in spring and by propagation by cuttings in early summer. We recommend division, because sowing is unpredictable.

Gorgeous colours of Amsonia hubrichtii in autumn!

Division

You can divide Amsonia’s woody stump about every four years, once well established.

1. Choose a healthy clump
2. Using a well-sharpened spade, cut several sections from the outer edge
3. Replant immediately in chosen spot in garden in well-prepared soil

Propagation by cuttings

1. In summer, take semi-woody stems of about 15 cm and plant them in buckets in a moist, sandy compost mix
2. Firm compost around each cutting
3. Place cuttings in a sealed plastic bag to encourage rooting
4. Pot on in autumn or the following spring after frosts

Sowing

Under favourable conditions, Amsonia self-seeds. However, if you want to propagate it from seed, nothing could be simpler.

1. Sow the seeds you collected after flowering in a seed tray under a cold frame in winter or at the very start of spring on the surface of a good, well-draining compost
2. Pot up seedlings into individual buckets
3. Plant young plants in garden once risk of frost has passed
4. Water well to ensure establishment

Discover our tips and tricks to succeed in sowing seeds on our blog!

Companion plants for Amsonia

Amsonias are among those perfect perennials to brighten sunny or shaded areas of garden alongside other summer-flowering perennials. With their both bushy and airy habit, and their pastel-blue flowering, they bring lightness and country charm to naturalistic gardens and add to the appeal of romantic gardens. Planted in small groups, they create moving, wild scenes and fit into colour harmonies of cool blues or whites or into more complementary blue/yellow combinations.

An example of a pairing: Salvia nemorosa ‘Caradonna’, Amsonia orientalis, Selinum wallichianum (or Cenolophium denudatum), Aquilegia vulgaris ‘Munstead White’ and Allium christophii

For delicate, romantic atmosphere, plant a few clumps of Amsonias alongside shrub roses, peonies, whose often bare and unsightly bases they will conceal, Agapanthus or Calamintha.

Soothing, luminous blue of the flowers, and their abundance, will give a fresh, charming touch in a blue garden, alongside ageratum, campanulas, blue-flowering salvias, gentians, hardy geraniums such as ‘Blue Cloud’, ‘Azure Rush’, Nepeta manchuriensis ‘Manchu Blue’, Polemonium reptans ‘Blue Pearl’, iris …

In bolder combinations, the azure tone of its flowers will contrast with yellow, red or orange flowers of summer-flowering perennials such as daylilies, geums, alchemilla, lupins, Kniphofias, Rudbeckias, Welsh poppies.

They will bring a fresh note to a bed of loose-habited perennials such as paniculate Phlox, agastaches, Eupatorium coelestinum, loosestrifes, vernonias, tansy ‘Isla Gold’, or to perennials for moist soil such as astrantias and camassias.

A contrasting example: Amsonia tabernaemontana var. salicifolia, Euphorbia cornigera ‘Goldener Turm’ and Geum ‘Totally Tangerine’

In late-summer scenes, they will keep company with Japanese anemones and asters, which will take over flowering into autumn.

Grasses for moist soil such as Japanese Hakone grass (‘All Gold’) or Miscanthus with colourful autumn foliage (‘Graziella’, ‘Purpurescens’) will accompany the beautiful golden and coppery tones of Amsonia’s autumn foliage.

→ Discover other ideas for pairing Amsonia in our advice sheet !