University of Vermont Extension
Department of Plant and Soil Science
Anytime News
Article
BEAUTIFUL
BLUESTARS
Dr. Leonard Perry, Extension
Professor
University of Vermont
While
some gardeners may plant bluestars for their blue flowers in early
summer, this
is one of those rare perennials with three seasons of interest.
Once planted, this low maintenance plant
needs little attention except to admire its beauty.
Bluestars
(Amsonia), native to the south and
central U.S, is named for an 18th century Virginia physician and
scientific
traveler in America, Dr. Charles Amson. So it is appropriate for
native and
naturalistic meadow plantings, as well as massed in borders or where
you want a
touch of blue. The blue flowers are
small (about 1/2-inch wide) and, as the name indicates,
star-shaped. They are borne in clusters (panicles) at stem
ends, in some cases almost covering the plant for about 3 to 4 weeks
in early
summer in the north, late spring farther south.
This is one of those perennials some refer to
as an “instant shrub”. Arising from the
ground in spring, by summer it creates an upright, mounded shrub
effect from 2
to 4 feet tall, depending on the species and growing conditions.
The
long, narrow fruit pods (follicles) after bloom also are very
attractive. It is one of the few perennials with very nice
fall color—a soft golden yellow. A member of the Dogbane family,
related to the
perennial periwinkle (Vinca) as well
as the tropical frangipani (Plumeria),
bluestars have a milky sap making them resistant to feeding by deer,
other
mammals, slugs and snails.
Bluestars
require some cutting back in fall or early spring to a few inches
above the
ground. Full sun is needed for best
growth and if too much fertility, or in too much shade, plants can
become
leggy. If this is the case, either stake
or cut back about half-way after flowering. If in a long season and
hot climate, you can
cut back then to about 10 inches high.
Plants
also may be divided in spring or started from seeds. Soak seeds
overnight in
warm water, or hold in the moist cold (40 degrees F) for four to six
weeks before
sowing. Plants shouldn’t need dividing
for at least 10 years, perhaps much longer if plenty of space around
them and
they remain healthy and blooming yearly.
Being
tolerant of many conditions, bluestars are low maintenance. Keep any
of the
bluestars well-watered for the first season after planting. Once
established they can tolerate some
drought. Mulching will help conserve
soil moisture. Fertilize lightly, if at
all, to avoid leggy growth. A dressing
of compost around plants in spring may be all this is required.
A
well-drained, moist soil is best although soil preference will vary
with
individual species as they are native to different habitats. The
Willow bluestar (A. tabernaemontana) and the Shining bluestar
(A. illustris) can be found naturally and grow well near
water and
in damp areas. The Downy bluestar (A. ciliata) and the Ozark
bluestar (A. hubrichtii) can be found naturally
and grow well in drier sites. There are
about 20 species, but only a handful are available at garden centers
and nurseries.
The
Ozark bluestar, sometimes called Arkansas or threadleaf bluestar,
was chosen by
professionals in the Perennial Plant Association as Perennial of the
Year for
2011. Like most bluestars the leaves are
longer than wide, but the leaves of this species are quite narrow.
One common name indicates its origin, found
in 1942 in the Ozark mountains of Arkansas by naturalist Leslie
Hubricht. It grows best in USDA zones 6 to 8, sometimes
into zone 5. While it can reach 3 feet
high and wide in warmer climates, it may be less robust in cooler
climates.
The
most common bluestar is probably the Willow, the species named for
German herbalist J.T.
Tabernaemontanus. While most bluestars only may grow into zone 5,
this one is
hardy in zones 3 through 9, and is found in moist woodlands. Its
flowers are
slate blue and the leaves wider than other species. Its fruit pods
are held
upright, unlike some other species whose pods hang down.
Eastern
bluestar, a variety (salicifolia) of the Willow, has leaves
five to 10
times as long as wide, like willow leaves (the species name is
similar to the
scientific name for willow). The Willowleaf bluestar has blue
flowers with
white centers. The Shining bluestar is similar to the Willow, only
the seedpods
hang down rather than being erect and upright, the leaves are more
shiny, and
the flower clusters are smaller. The
Downy bluestar is named for the fringe of soft hairs on leaves and
stems when
young. Otherwise this species is similar
to the Ozark in growing conditions and appearance.
Trials
of several in this genus at the Chicago Botanic Garden (zone 5)
several years
ago resulted in good ratings for most.
The only ones rating lower due to chlorotic leaves, likely due to
high
pH soil conditions, were the Downy and the Dwarf (A. montana)
species. The
latter are similar to the Willow and often seen listed as a variety
of it, only
this one has wider leaves, and a shorter and compact habit. An even
shorter cultivar (cultivated variety)
of the Dwarf, ‘Short Stack,’ only reaches about a foot tall so is
good for rock
gardens.
The complete results of these
trials, as well as of many other perennial genera, can be found
online under
the Research section at the Chicago Botanic Garden
(www.chicago-botanic.org/research/plant_evaluation/#notes).
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