Amsonia Identification and other Amsonia Mysteries

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Robert Pavlis

The genus Amsonia is a collection of herbaceous plants that are not well known in gardens, but they should be more popular. They are great plants, flower well, are North American natives and some are very drought tolerant. They are also more cold tolerant than believed. The various available species are similar and very often misnamed. It is quite common to find pictures in books and on the net that are misidentified.  In today’s post I will try to sort out the differences to help you identify plants.

Amsonia 'Blue Ice'
Amsonia ‘Blue Ice’ by Robert Pavlis, GardenMyths

Amsonia

Amsonia plants are 1 to 3 feet (30-90 cm) tall and produce blue flowers. The flower of each species is very similar and plants are best identified by their leaf and stem characteristics, which unfortunately are also fairly similar.

Leaves can be divided into two types; narrow needle-like and wider willow-like. The group of plants with narrow needle-like leaves include Amsonia ciliata and Amsonia hubrechtii. The group having willow-like leaves includes Amsonia tabernaemontana, Amsonia tabernaemontana ‘Montana’, Amsonia illustris, and Amsonia ‘Blue ice’.

Amsonia ciliata

Amsonia ciliata has fairly narrow leaves, around 4 mm wide. It has hairs on new leaves and on the stem which differentiates it from Amsonia hubrechtii. The flower clusters are held higher above the stem than some other Amsonia, making it one of the showiest in the genus. Amsonia ciliata ‘Spring Sky’ is a very showy cultivar with extra large flowers. Hardy to zone 4.

Microbe Science for Gardeners Book, by Robert Pavlis

Amsonia hubrechtii

Amsonia hubrechtii has extremely narrow thread-like leaves, less than 2 mm wide.It turns an exceptional gold-yellow color in the fall–the best fall show in the genus. Very drought tolerant and hardy to zone 4.

Amsonia illustris

Amsonia illustris looks very much like Amsonia tabernaemontana, but it’s leaves are shinier, and thicker in substance. This species has pendent seed pods as opposed to upward-facing for Amsonia tabernaemontana . Hardy to zone 4.

Amsonia tabernaemontana

Amsonia tabernaemontana is a bit more common in the nursery trade and has dull green, willow like leaves. It is a variable plant and several varieties and related species have been defined. It is drought tolerant and hardy to zone 3.

Amsonia tabernaemontana ‘Montana’

Amsonia tabernaemontana ‘Montana’ is more popularly known as Amsonia montana, but it is not a recognized species. It is shorter (2 feet, 60 cm) than Amsonia tabernaemontana (3 feet, 90 cm) and it has smaller leaves. It also differs in having flowers with bluntly rounded petal tips rather than pointed apices like most of the other bluestars.

Amsonia ‘Blue Ice’

Amsonia ‘Blue Ice’ is quite a distinct variety of unknown origin. It is sometimes incorrectly called Amsonia orientalis ‘Blue Ice’. This plant is much shorter (1.5 ft, 45 cm), has dark green willow-like leaves, and the darkest blue flowers of any amsonia. Hardy to zone 4. This is my pick for best amsonia, but I have not yet grown Amsonia hubrechtii.

Cultural Information

For good information on culture and some other lesser known species have a look at this reference by Rick Darke and this one by the Chicago Botanic Garden.

References:

1) Amsonia in Cultivation by Rick Darke: http://www.rickdarke.com/Amsonia.pdf

2) An Evaluation Study of Hardy Amsonia: http://www.chicagobotanic.org/downloads/planteval_notes/no18_amsonia.pdf

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

3 thoughts on “Amsonia Identification and other Amsonia Mysteries”

  1. I have blue ice Amsonia and I love it. It is basically maintenance free and a beautiful shrub. I have it in full sun.

    Reply
  2. Most interesting post.
    I have little experience with Amsonia. I have a clump of Amsonia tabernaemontana I grew from NARGS seeds. It is healthy and growing well but this year is its 3rd if not its 4th and it has not yet bloomed. Perhaps I have it in too much shade (it gets an average of 3 hours of sunshine a day, more in mid-summer). Do you think that might be the problem?

    Reply
    • They like full sun–so at least 6 hours a day. I have 4 species/varieties and all were grown from seed. From seed they usually bloom in their second year.

      Reply

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