Threadleaf bluestar

Sun

Full sun to partial shade; full sun produces sturdier stems and usually stronger autumn colour.

Water

Water regularly during the first growing season. Once established, water during prolonged dry spells; it tolerates some drought but grows best with moderate moisture.

Soil

Average, well-drained soil, including clay if drainage is adequate. Avoid persistently waterlogged ground and excessive fertiliser.

Height

2-3 ft (0.6-0.9 m)

Spread

2-3 ft (0.6-0.9 m)

Flowers

Late spring to early summer; clusters of small, pale blue, star-shaped flowers.

Foliage

Very narrow, soft, green leaves densely line upright stems, giving a feathery appearance; golden yellow in autumn.

Growth

Slow to moderate; usually takes two or three growing seasons to form a substantial clump.

Care needed

Low

• Water deeply through the first growing season, allowing the surface soil to dry slightly between waterings.
• Apply a thin layer of compost in spring; avoid high-nitrogen feeding, which encourages floppy growth.
• Mulch to conserve moisture, keeping mulch away from the crown.
• Choose a sunny position to reduce the need for staking.
• Leave established clumps undisturbed unless they outgrow their space; their woody roots make division difficult.

Pruning. Leave stems standing through autumn to enjoy the golden foliage, then cut them close to ground level in late winter before new shoots appear. If plants become floppy, shorten stems by up to one-third just after flowering.

Late winter

Cut down dead stems before new growth begins.

Spring

Plant container-grown plants and water them in thoroughly.

Mid-spring

Apply a thin compost dressing and renew mulch without covering the crown.

Early summer

After flowering, shorten floppy stems by up to one-third if needed.

Summer

Water new plants regularly and established clumps during prolonged drought.

Autumn

Leave the yellow foliage intact until it fades; remove unwanted seedlings if they appear.

• Plant repeated groups through a perennial border to provide a fine-textured framework after the flowers fade.
• Combine with coneflowers, black-eyed Susans and ornamental grasses in meadow-style planting.
• Use beside broad-leaved plants such as false indigo to create a clear foliage contrast.
• Place where low autumn sunlight catches the golden foliage, with asters or dark seedheads nearby.

Garden styles it suits: New perennial (prairie), Native meadow, Cottage garden, Autumn colour, Low-maintenance and Wildlife garden.

Plant it with: Purple coneflower, Black-eyed Susan, Switchgrass, Little bluestem, Blue false indigo and Aromatic aster.

Wildlife: Flowers provide nectar for visiting insects, including butterflies. Deer generally avoid the foliage, although no plant is completely deer-proof.

• Flopping stems: increase sunlight, avoid rich feeding and shorten stems after flowering if necessary.
• Root or crown rot in wet soil: improve drainage or move the plant to a better-drained site.
• Leaf scorch during prolonged drought: water deeply and mulch, especially while plants are establishing.

The milky sap can irritate human skin, so wear gloves when cutting or dividing. Ingestion may cause stomach upset, but species-specific toxicity and severity in cats, dogs and horses are not well documented; keep all parts out of reach of chewing pets and do not use it as forage.

• Eastern bluestar (Amsonia tabernaemontana)

  Has noticeably broader, willow-like leaves rather than the very narrow, threadlike leaves of threadleaf bluestar.

• Fringed bluestar (Amsonia ciliata)

  Also has narrow leaves, but typically has conspicuous fine hairs on young stems and leaf margins; threadleaf bluestar is largely hairless.

Amsonia honours physician John Amson, hubrichtii honours American naturalist Leslie Hubricht, and threadleaf bluestar describes the narrow leaves and blue, star-shaped flowers.

Propagation. Sow fresh seed outdoors in autumn; germination can be slow and uneven, and a period of winter cold helps. Take softwood stem cuttings in early summer. Large clumps can be divided in early spring, but the tough, woody rootstock makes this difficult.

Accepted botanical name

Amsonia hubrichtii

In the US and Canada

Native in the lower 48 states.

Native range

Arkansas and Oklahoma.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.