How-To · Arkansas Bluestar · Southeast
A creek-bank perennial from the Ouachita Mountains that wants lean soil, full sun and almost nothing else: how to plant threadleaf bluestar this fall, when to cut, and why the gold is worth the wait.
In this piece
I.A snail collector's bluestar
In May of 1940, a collector named Leslie Hubricht pressed a specimen along a stream three miles west of Birta, in Yell County, Arkansas. Hubricht worked at the Missouri Botanical Garden and is remembered chiefly for snails: over a long life he named 81 species of North American land snail. Two years later he showed the Garden's Robert Woodson another dried specimen of the same plant, this one from Garland County. Woodson grew live plants to be sure, and in 1943 he described the species in Rhodora as Amsonia hubrichtii.
The wild plant is a narrow endemic of the Ouachita Mountains of west-central Arkansas and southeastern Oklahoma, a plant of rocky creek banks and the scour zone of small streams, where floods knock the vegetation back and the soil is thin and stony. NatureServe ranks the species as globally vulnerable, with some 57 known occurrences in seven Arkansas counties, most of them on national forest land and considered stable. The genus name reaches further back: Amsonia honors Dr. John Amson, an eighteenth-century physician and one-time mayor of Williamsburg, Virginia. The often repeated "Charles Amson" has no historical basis.
A plant of creek banks and scour zones, where floods knock everything back and the soil is thin and stony. Remember that when you are tempted to feed one.
In the garden, Arkansas bluestar is two plants in one year. In April and May, pale powder-blue stars about half an inch across open in clusters at the tips of the stems. Then the flowers go, and the real show begins: a billowing, shrub-sized mound of needle-fine leaves, soft enough to run a hand through, which turns a clear, bright gold in autumn. The Perennial Plant Association named the species Perennial Plant of the Year for 2011, and the University of Georgia made the plant a Georgia Gold Medal winner in 2009.
II.Where to plant
Start from the creek bank. Give Arkansas bluestar full sun, average to lean soil, and good drainage. Rich soil and shade both make the stems grow soft and tall, and a soft clump falls open in the middle by midsummer like a badly tied sheaf. Missouri Botanical Garden suggests a little afternoon shade in hot climates to make the flowers last longer, which is worth weighing here; the trade is a little less gold in fall, since Missouri Botanical Garden, North Carolina State and Mt. Cuba all note that the best color comes in full sun.
The plant is drought tolerant once settled, deer and rabbits leave the foliage alone, and Mt. Cuba Center, which grew twenty kinds of bluestar for ten years in clay-loam with water only in the first season, rated A. hubrichtii 4.7 out of 5 and among the top performers in the trial. Size is two to three feet tall and as wide, and the species is hardy in zones 5 to 8 by the most conservative count; Aiken at 8a is comfortably inside every published range.
Amsonia hubrichtii
Arkansas bluestar, threadleaf bluestar
- 2 to 3 ft
- Full sun
- Lean soil
- Zones 5 to 8
- Native
- Gold fall color
Powder-blue stars in spring, then a soft green cloud of threadlike leaves all summer, then gold. Long-lived, deer resistant and nearly trouble free, for the sunny border, the dry bank and the gravel garden.
Good places for a bluestar
Set a single plant where low autumn light will come through the gold from behind, at the corner of a path or the front of a sunny border. Repeat three or five down a long border for rhythm, or mass them on a bank. In a dry garden, threadleaf bluestar pairs well with the lean-soil plants we wrote about in Gardening in Sand, and the fine texture makes a good foil for anything coarse: the big pinnate leaves of staghorn sumac behind, say, burning scarlet while the bluestar burns gold.
III.How to plant, and how long to wait
Fall is the season. Plant from October into early December, while the soil is still warm, so roots can grow through the cool months before the plant has to support new growth in spring. The reasons are laid out in full in Plant It in the Cooling.
Step 1: Choose and prepare the spot
Pick the sunniest spot you can, with soil that drains after a rain. Do not add compost or fertilizer to the planting hole; on heavy clay, loosen a wide area and plant slightly high rather than enriching the soil. Remember that the clump will reach three feet across.
Step 2: Space the plants
North Carolina State gives a spacing of one to three feet. Set plants two and a half to three feet apart if you want each clump to read as a separate mound; closer, about eighteen inches, for a continuous drift. The University of Georgia suggests groups of three or more.
Step 3: Plant and water
Set the crown at the same depth as in the pot, firm the soil, and water deeply. Water weekly through the first fall in dry spells and through the first summer. After that the plant should need watering only in a long drought.
Step 4: Be patient
Arkansas bluestar takes one to two years to fill out, and the University of Georgia calls the plant moderately slow to establish. The first year looks thin. By the third year the clump looks like the photographs, and from then on the plant is long-lived and rarely needs attention.
Field Note
Choose the spot carefully, because you will not want to move the plant later. Iowa State Extension notes that the dense crown is hard to divide or move once established. Division is rarely needed; if you must, divide in spring, with a sharp spade and a strong back.
IV.The two cuts
An established bluestar needs pruning at most twice a year, and only one of those cuts is essential.
The optional cut, after flowering
If a clump flops, or you want a tighter mound, trim the stems back after flowering in late spring. Sources disagree on how much: Missouri Botanical Garden suggests about six inches, Iowa State as much as half. North Carolina State treats the cut as optional, needed only if the plant is floppy. In full sun and lean soil you may never need the trim. In richer soil, a harder cut in late May, toward the half that Iowa State suggests, gives a lower, denser plant that stays upright into fall.
The essential cut, in late winter
After the gold, the foliage turns a warm tan and stands through the winter, which is part of the plant's appeal. Leave the stems up for winter. In late winter or early spring, before new shoots emerge, cut them down. Mt. Cuba Center suggests leaving twelve to eighteen inches of stem rather than cutting to the ground, because native bees nest in the hollow stubs; the new growth covers the stubble within weeks.
Field Note
Like milkweed, bluestar belongs to the dogbane family, and the cut stems bleed a milky latex that can irritate skin. Wear gloves for both cuts. The same sap is why the deer leave the plant alone. Our earlier piece Milkweed and the Memory of Wings follows the same family through a very different plant.
Propagating your own
The University of Wisconsin reports that softwood cuttings from non-flowering stems, taken in early summer, root in three to four weeks. Seed is slow and erratic. No tested germination method has been published for this species, but in a related bluestar a warm period followed by cold, moist stratification greatly improved germination, so that is the method to try first.
Pests and problems
Very few. Mt. Cuba recorded only minor rust and some yellowing of leaves over ten years. Nearly all garden failures come from too much shade, too much fertilizer or wet soil, and all three show up first as flopping.
V.The rest of the clan
Arkansas bluestar is the showiest of the genus in fall, but the Southeast has native bluestars too. A comparison for the gardener choosing one:
| Species | Native to | Leaves | Best site | Mt. Cuba rating |
|---|---|---|---|---|
| A. hubrichtii, Arkansas bluestar | Ouachita Mts., AR and OK | Threadlike | Sun, lean soil | 4.7 |
| A. tabernaemontana, eastern bluestar | Eastern and central US, including SC | Broad, willowy | Sun to part shade, moister soil | 4.6 |
| A. ciliata, fringed bluestar | Sandy open woods; common in SC coastal plain and Sandhills | Narrow | Deep sand, sun | 3.9 to 4.9 by form |
| A. ludoviciana, Louisiana bluestar | Rare; GA outcrop edges, Gulf Coast flatwoods | Narrow, felted beneath | Sun, well drained | Not reported |
The fringed bluestar is the one that grows wild in the deep sand of the Carolina Sandhills, our own country, and is worth knowing for that alone. 'Blue Ice', sold as a compact bluestar of about fifteen inches, is now usually treated as a form of the Eurasian Amsonia orientalis rather than a native. The full range we grow is in our Amsonia collection; the eastern, Louisiana and dwarf bluestars come and go with the seasons.
Plant now, wait two autumns
We have Arkansas bluestar on the bench this fall. Put three in the sunniest, leanest corner of the garden this month, cut them down in February, and leave them be. The second autumn they will be good; by the third, the gold will stop people on the path.
References
- Woodson, R. E. Jr. "A New Amsonia from the Ozarks of Arkansas." Rhodora 45: 328 to 329 (1943).
- Pringle, J. S. On the naming of Amsonia and Dr. John Amson. SIDA 21(1): 379 to 387 (2004).
- NatureServe Explorer. "Amsonia hubrichtii." explorer.natureserve.org
- Mt. Cuba Center. "Amsonia for the Mid-Atlantic Region" trial report. mtcubacenter.org
- Missouri Botanical Garden Plant Finder. "Amsonia hubrichtii." missouribotanicalgarden.org
- North Carolina Extension Gardener Plant Toolbox. "Amsonia hubrichtii." plants.ces.ncsu.edu
- University of Wisconsin Extension. "Arkansas or Thread-leaf Blue Star." hort.extension.wisc.edu
- Iowa State University Extension. "Bonkers for Bluestars." yardandgarden.extension.iastate.edu
- University of Georgia CAES. Georgia Gold Medal Winners, 2009. caes.uga.edu
- South Carolina Native Plant Society. "Amsonia ciliata." scnps.org
