Dr. Leonard Perry, Extension Professor
University of Vermont
Bluestars (Amsonia) are excellent low-maintenance perennials for early summer bloom. With flowers generally a pale blue, bluestars are different from many perennials in having three seasons of interest like many shrubs. In addition to their early summer blue flower color, they have attractive summer foliage and habit, then golden fall foliage.
Bluestars are so named for the small blue star-shaped flowers produced in clusters on the ends of stems. Later in the season cylindrical pods are produced, either hanging down or upright depending on species. Leaves vary with species too, from very narrow and threadlike to lance or egg-shaped (termed "lanceolate" or "ovate").
The sturdy stems form an "instant" shrub each spring, growing from the ground to produce a vase-shaped mound about three feet tall and up to five feet across depending on species. Plants slowly increase in size, so only may need dividing every ten years, if then. There are no significant pests or diseases on bluestars, and with their milky sap they are deer resistant.
Bluestars grow in a variety of habitats, depending on species. All are native to the Northern hemisphere, with some native to North America. Although they prefer moist soils, I find they tolerate some drought. During dry periods use mulch, and water well, to minimize stress on the plants and for best growth and flowering. Most flowers and strongest stems are produced in full sun. Many species will tolerate some shade but may be more leggy, need staking, and have fewer flowers. If plants become leggy, cut back to about a foot high after bloom to produce more compact plants.
Of the dozen or so species, and one cultivar, generally available, all have proven hardy in trials by Richard Hawke at the Chicago Botanic Garden in USDA zone 5. The dark blue cultivar 'Blue Ice' may be listed as hardy to zone 4 (much of Vermont). The most common species (tabernaemontana) may be hardy to zone 3, and is native to the eastern United States. A species (illustris) native to the central United States is similar, only with hanging seed pods, thicker leathery leaves, and likely hardiness to only zone 5. Both these species were best in the Chicago trials, especially in regards to flower display. While the flower clusters of the first may reach six inches long and four inches wide, the flower clusters of the latter species may reach three inches long and wide.
A natural variety of the eastern species (tabernaemontana var.
salicifolia) has much more narrow leaves, five to ten times longer
than wide, and is native to the southeastern states. This also bloomed
quite well in the Chicago trials, as did the Arkansas amsonia (hubrichtii).
Both the Arkansas amsonia and the downy amsonia (ciliata) have feathery
foliage, and may only be hardy to zone 5. The downy amsonia, however,
had the fewest flowers of any in these trials.
You can use bluestars as specimen plants in island beds, massed in borders, mixed into shrub borders, or scattered in naturalistic meadow gardens. In addition to these sites, some can be placed near ponds and streams (tabernaemontana and illustris), while others (ciliata and hubrichtii) can the placed on dry sites such as gentle slopes. Just make sure to note the hardiness of species if you are in a colder area, or place them in more protected and warmer microclimates.
If you have the space, like low-maintenance perennials, and want three seasons of use in the garden beginning with early summer blooms, consider bluestars for your landscape. The blue color complements most other colors in the garden, and the foliage provides a nice backdrop for later summer blooms.
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