Amsonia is a relatively small genus with a few species that offer outstanding ornamental value. Amsonia illustris is perhaps the boldest of the Amsonias, a little taller and showier with shiny green leaves and larger blue flowers.
Known as the ‘Shining Blue Star’ this is a striking, smooth perennial that maintains a graceful appearance throughout the growing season. The alternate shiny leaves are willow-shaped, narrowly lanced to 15cm (6in) long, leathery and shiny on the upper surfaces. The foliage stays green through summer and turns a brilliant gold in the autumn.
Amsonia illustris is a low-maintenance plant, that form tight clumps with a stout, vase shape. They flower reliably year after year, they are not pushy or invasive, they are rarely fussy about soil or situation and they are very hardy. During April and May, the star-shaped, rich, light blue flowers appear, they are clustered in panicles at the tops of the stems and have a delicate scent that is highly attractive to butterflies.
At three or more years, they can reach between three and four feet tall and be equally wide. If height becomes an issue, it can be pruned back a third or a half in mid-summer, and new growth will appear almost immediately.
They do not need regular division, staking or fertiliser, as this may cause plants to flop. The plants grow happily in sun or in dappled shade and cope well with drought. You will seldom have reason to water this tough, hardy perennial. It performs best when cut back to the ground in late winter before new growth occurs in spring.
Adaptable to many soil conditions as long as they drain well-including heavy clay. Extremely tolerant of drought, thriving with no supplemental irrigation in summer. Full sun to quite a bit of shade. This is an extraordinary long lived designer perennial that deserves wider use.
Amsonias prefer moist soils and grow well in any garden soil, including clay. They will grow in full sun or semi-shade. The plants are drought tolerant and generally do not wilt in dry spells. Drier conditions reduce the height of the plant, but they will flower well every year. In drier situations they are happiest in semi-shade.
Amsonia germinate best if they experience a cold period. If you are planting in autumn to winter you can use the natural method, simply planting in a seed tray and placing the tray outdoors until the spring. Otherwise, at warmer times of the year it will be necessary to artificially simulate winter temperatures by using the method of stratification.
Fill 7cm (3in) pots or trays with a good soil-based compost. Sow the large seeds onto the surface and gently firm down. Cover the seeds with a sprinkling of fine grit.
The Natural Method: Autumn / Winter
Fill seed trays with a good soil-based compost. Sow the large seeds onto the surface and gently firm down. Cover the seeds with a sprinkling of fine grit. Place the tray or pots in a cold frame, an unheated greenhouse or under a shaded hedge. Keep the soil damp but not wet and do not exclude light. Patience may be needed as germination can be very slow taking anything from 30 to 365 days, although germination can be quicker if temperatures are around 15 to 20°C (16 to 68°F). When seedlings are large enough to handle, transplant them into 7cm (3in) pots and grow them on in cooler conditions until large enough to move outdoors. Keep the seedlings in light, but not full sun and plant out in autumn.
Stratification: Spring / Summer
If you require seedlings quicker, you may wish to try stratifying the seeds – this method simply exposes the seedlings to temperature changes, as they would do if germinating naturally.
Sow the large seeds onto the surface of trays or pots containing good soil based compost and gently firm down. Place in a propagator or seal inside a polythene bag and keep at a daytime temperature of 13 to 15°C (55 to 60°F) for 2 to 3 weeks. After this time, move the tray to a refrigerator to cool (not a freezer) this will expose the seeds to temperatures of around 4°C (39°F) which will simulate the cold of winter. Leave them in the fridge for 3 to 6 weeks, after which remove the tray and place somewhere with normal daytime temperatures. Keep the compost moist at all times.
This method usually works for some of the seedlings but some seeds may wait for spring before emerging regardless of when or how they are sown. Prick out any seedlings that have germinated into pots to grow on, then place the tray back in the cold frame so that any seeds that remain may germinate naturally.
Plant Amsonia at a distance of 30cm (12in) apart, in any well-drained soil in sun or dappled shade.
Amsonias plants are slow to get going in the garden, these slow-growing perennials form tight clumps that do not need regular division or staking. They can, if needed be divided in early autumn and replanted straight into the soil.
Due to their milky sap, Amsonias are often bypassed by foraging mammals, which makes them somewhat resistant to deer and other pests. Although they only contains two to five per cent latex which can irritate the skin, this slight toxicity has one major advantage - slugs and snails never damage the emerging shoots.
The flowers can be cut and used in floral arrangements, wear gloves and sear the end of the stems in a flame to stem the milky sap before popping in a vase.
Amsonias have some of the funniest-looking seeds around. The seed pods are long tubes that are filled with cylindrical brown seeds arranged end-to-end. The seeds ripen in late summer to autumn, quite a long time after the plants bloom. Harvest them when the pods are quite dry and tan in colour, but before they split apart lengthwise to drop their seeds. They germinate quickly when sown straight away. If stored, the seeds may need to go through a cold season before germination.
Cottage gardens, Borders and beds, Low maintenance gardens, Shade and Woodland gardens.
Amsonia is a genus of about twenty species, native to temperate climates in North America, Europe, and Asia. It occurs in moist to wet woods, floodplains, and riverbanks.
Native to the eastern US, Amsonia illustris can be found in wet soils from eastern Kansas and southern Missouri, Nevada and south to Texas. It most frequently occurs in sandy or rocky soils on gravel bars or along streams in the Ozark region of the state.
The latest taxonomical wisdom places them in the apocynaceae family, which they share with several hundred other genera, including Asclepias and Vinca.
The genus Amsonia is named for Charles Amson, a U.S. traveller-scientist who lived in the 18th century.
The specific epithet illustris is from the Latin illustrissimus meaning bright, shining, brilliant, illustrious.
Commonly known as the ‘Shining Blue Star,’ is named for its glossy leaves and light blue blooms.
It goes by the name of Ozark Blue Star, since this plant is native to the Ozark Mountains, and is also known by a number of other names including Showy Blue Star, Woodson Ozark Bluestar, Missouri Blue Star and Swamp Bluest
- Additional Information
Average Seed Count 12 Seeds Family Apocynaceae Genus Amsonia Species illustris Common Name Shining Blue Star, Ozark Blue Star Other Common Names Showy Blue Star, Woodson Ozark Bluestar, Missouri Blue Star and Swamp Bluest Hardiness Hardy Perennial Flowers Powder-blue with five slender petals. Natural Flower Time May to June Foliage Shiny green lanceolate leaves Height 90 to 120cm (36 to 48in) Spread 90cm (36in) Position Full Sun to Part Shade Soil They grow well in any garden soil including clay. Germination 10 to 40 days Notes Often treated as Annual.