There’s a lot to love about Amsonia ‘Storm Cloud.’ First are its tufts of starry periwinkle blue flowers that hover above foliage in late spring. Next are willowy leaves and a bushy habit that bring contrast and texture to the display. There’s also the advantage of carefree growing with little maintenance needed.
Perhaps most significant is that all this ornamental and ecological value comes from a U.S. native selection. The species is native to the Southeastern part of the country. The flowers and foliage host pollinators, and there’s little demand for excess resources regarding water and fertilizers.
Designated as the 2024 Landscape Perennial of the Year by Proven Winners, ‘Storm Cloud’ also tops plant trials. The heat-tolerant, deer-resistant selection is a valuable perennial addition.
‘Storm Cloud’ Amsonia Overview
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What is ‘Storm Cloud’ Amsonia?
This plant dazzles with blue flowers and rich foliage.
‘Storm Cloud’ is an herbaceous perennial plant with unique blue-hued flowers. It is an exciting discovery among a native species. Amsonia is a small genus mostly native to the United States, with some occurring in Asia and the Mediterranean. A. tabernaemontana, or bluestar, is highly ornamental and the most popular of the group.
‘Storm Cloud’ shines in late spring with loose, whole clusters of periwinkle blue flowers. Attractive, willowy foliage in deep olive green with golden-yellow fall color brings multiseason appeal. Even when the bushy perennials aren’t in flower, they provide a handsome backdrop to summer and fall bloomers.
This native selection grows two to three feet tall and three to four feet wide. Its size makes it ideal for the middle of the perennial border or as a shrub replacement. With their highly decorative flower heads, they’re exceptional in groups and as stand-alone specimens.
Companion Plants
Bluestar embellishes naturalized garden schemes among looser plantings. Contrasting foliage like yarrow, nepeta, heuchera, and hosta anchor the display. Use them to accent the perennial border, native planting arrangement, pollinator, rain, and rock gardens, and woodland edges.
They complement spring-flowering plants like bulbs, lilies, and phlox. Echinacea, hardy hibiscus, salvia, and ornamental grasses add color and movement throughout the warm season.
Awards
This exceptional native is famous for its low maintenance and easy care. The plants are durable and have few landscape problems. Their unique forms enliven the planting arrangement with abundant baby blue florets and rich foliage. Butterflies, hummingbirds, bees, and other pollinators flock to the large, nectar-rich flower clusters.
In addition to the Landscape Perennial of the Year designation, ‘Storm Cloud’ tops plant trials at Michigan (2022) and Mississippi (2021) State Universities.
Characteristics
Starry blooms and dark stems create a captivating display.
Sparkling starry blooms are the standout feature of ‘Storm Cloud,’ but the intrigue doesn’t end there. As temperatures warm in the spring, new stems emerge nearly black. They hold their dark color through flowering, lightening as summer progresses.
Willow-shaped leaves densely whorl around the smooth stems. They emerge dark olive green with silver veins. As summer moves to fall, they become lighter green and yellow before turning gold in cool autumn temperatures. They then become brown and dry with winter dormancy.
The plants produce multiple stems that rise two to three feet tall. In late spring and early summer, flowers appear in panicles on the tips of stems, with the potential for reblooming. The flowers are lovely on the stem and in fresh arrangements.
Each ¾-inch tubular floret flares to a pointed star shape. After flowering, elongated bean-like seed pods develop. The fruits dry and split open when ripe.
When cut or damaged, stems produce a milky sap to seal the wound and deter predation. If ingested, the sap is toxic to people and pets and can cause contact skin irritation. On the plus side, deer seldom damage the native bloomers.
Bluestar has few pests or disease problems. It is drought-tolerant and withstands heat and humidity. In optimal growing conditions, it’s a long-lived garden performer.
Native Area
Native to the Southeast, this plant thrives in varied conditions.
The species tabernaemontana occurs naturally in the Southeast, Eastern, and Central United States. It grows in open woods, thickets, plains, and wet, sandy sites. It spans a range of conditions and climates.
Renowned plantsmen Hans Hansen (Walters Gardens) and Tony Avent (Plant Delights Nursery) discovered the native selection among an Amsonia colony in Bibb County, Alabama. The plants grew wildly in wet, deep shade along a woodland stream. After trials in Michigan and North Carolina, they selected ‘Storm Cloud’ for its robust growth, compact habit, and prolific blooms.
Planting
Fall and spring are ideal times for planting perennials.
Fall and spring are the best times to plant perennials. However, if there is adequate moisture for strong root systems to develop, plant them anytime. Avoid planting during stressful conditions like high heat, drought, or freezing soils.
Plan for maturity so bluestar can grow in a permanent garden location. They develop long tap roots and spread 38-42 inches wide.
Dig a hole two to three times as deep and wide as the size of the root ball. Loosen any tightly wound, pot-bound roots so they can grow outward. Water plants deeply to settle the roots and soil.
‘Storm Cloud’ is sturdy and withstands winds and coastal exposures. If exposures are drying, supplemental irrigation helps maintain vigor.
The bloomers also grow well as singular container specimens. Ensure pots are large enough to house their robust roots. Provide consistent water, a quality potting mixture, and good drainage.
Transplanting
Fall is best for moving perennials to establish roots.
Bluestar seldom needs dividing, even after many years. If you need to move them, fall is optimal. It allows roots to get established before freezing temperatures. Water after planting or dividing and in dry conditions until winter dormancy. Natural fall and winter seasonal moisture is sufficient for dormant perennials.
Protect container specimens from drying winter winds and extreme conditions. Nestle them near the side of a house or among leaves, or move them to a dim, unheated space like a garage or basement to overwinter.
How to Grow
This adaptable cultivar is carefree and reliable. With a sunny location and moisture during intense dry spells, it needs little else to flourish. While ‘Storm Cloud’ is mostly self-sufficient, optimal cultural conditions promote the best growth and flowering.
Light
Full sun to partial shade keeps plants upright and healthy.
Place Amsonia in full sun to partial shade, with at least four to six hours of sunlight daily. In more shade, stems may droop and flop. They’ll benefit from staking or pruning in the shade. With ample sunlight, no staking is necessary for the upright growers.
Water
Deep, infrequent watering ensures strong roots and drought resilience.
The natives do best with regular moisture during their first growing season. Watering deeply, rather than frequently and shallowly, is best for root growth and moisture uptake.
Once established, average rainfall is usually enough to support growth. Bluestar are relatively drought-tolerant. Supplement with irrigation during dry spells and prolonged heat.
Brown, crispy leaves are signs of overly dry soils. Yellowing foliage may indicate wet earth outside of seasonal changes. Check the surrounding soil for dry or wet conditions to an inch or two deep. Increase or reduce irrigation accordingly.
If you’re growing them in pots, ensure the containers are well-draining and check the moisture level regularly. Reduce watering sessions in the winter, watering overwintered containers only when the soil feels dry.
Soil
Moist, well-drained soils with a neutral pH are ideal.
Ordinary soils with average moisture and good drainage are ideal for ‘Storm Cloud’ Amsonia. They prefer moist loams but tolerate various soil types, from sand to clay. A neutral soil pH of near 7.0 is best to prevent chlorotic (yellow) leaves later in the summer. Amend high-pH soils with aluminum sulfate if yellowing leaves are an issue (and they aren’t moisture-related).
In heavy clay soils, add composted organic material to the native soil to improve aeration, moisture retention, and drainage. Limit amendments to one-third of the native backfill. The rugged perennials don’t require rich soils. As with shady sites, branches flop in overly fertile soils.
Temperature and Humidity
This plant thrives in various climates with proper chilling.
‘Storm Cloud’ Amsonia tolerates a range of summer and winter temperatures in zones 3-9, making it suitable for northern and southern gardens. The plants withstand heat and humidity.
Cold stratification is a key temperature requirement for the species’ seeds to germinate. They need a 4-12 week chill period below 40°F (4°C), whether in the ground or refrigerated.
Fertilizing
Annual compost and occasional iron keep it thriving beautifully.
The cultivar doesn’t require fertilizer to thrive. If leafy stems are yellow early, add iron to green them up. An annual or twice-per-year application of compost is enough to support this plant, though.
Maintenance
Cut back dry stems in spring to encourage fresh growth.
Amsonia needs little ongoing maintenance. Cut back dry stems at the end of the season or leave them in place for added winter protection and overwintering insects. Remove them before or just after new spring growth emerges.
Cut plants back to six to eight inches after flowering to tidy up the plant’s appearance and encourage a new flush of growth. The early summer cut promotes a fresh, rounded form for the remainder of the growing season. It also helps keep stems upright in shadier conditions. Pruning isn’t essential to the plant’s health.
Mulch around plants with a three-inch layer, avoiding the stems. Mulch regulates soil temperatures and improves moisture retention.
Propagation
The best way to propagate ‘Storm Cloud’ Amsonia is through softwood cuttings. While the species propagates through seed, seedlings won’t be true to type. The plants hybridize naturally in the landscape. It may be best to remove seed pods to prevent self-seeding a different selection. Division, too, can be challenging due to disrupting the sturdy root systems of established plants.
Cuttings
Propagate by rooting softwood cuttings in moist, warm conditions.
Many perennials are well-suited to propagation through cutting and rooting fresh, pliable stems. ‘Storm Cloud’ Amsonia takes about two months to develop from cuttings for transplanting.
Here are the steps for softwood propagation:
- Cut a four-to-six-inch piece of a healthy green stem. It should snap when bent.
- Remove the foliage from the bottom ⅔ of the cutting (keeping at least two leaves intact). Keep cuttings moist until ready to pot.
- Optional: Moisten the cutting and generously coat the lower stem with rooting hormone.
- Tap off any excess rooting powder.
- Plant the cutting in at least two inches of moist, well-draining potting mix.
- Place the pot or tray in a bright, warm location, avoiding direct sunlight.
- Mist/water as needed, keeping the soil evenly moist.
- When the cutting resists a gentle tug, roots are in place and ready to be repotted.
- Plant the cuttings in four-inch pots and move them outside in mild conditions. New plants will be tender.
Growing From Seed
Sow seeds in the fall or after cold stratification for spring.
While the seedling won’t necessarily reflect ‘Storm Cloud,’ plants produce viable, easy-to-sow fruits. In the fall, collect dry pods and open them to sow directly. Plant them ½ inch below the soil surface. Direct sowing exposes seeds to their necessary cold stratification period.
If you’re not ready to plant, store the seeds in an airtight container in the refrigerator until ready to sow. Give them at least one month and up to two months of cold exposure. To prepare stored seeds for spring sowing, clip off the tip and soak them for two to three days before planting. It may take seeds up to ten weeks to sprout. Seedlings usually flower in their second growing season.
Division
Divide and transplant in spring or fall, keeping roots moist.
If you divide your selection for transplanting, dig them in spring or fall. Dig the whole plant and rinse away soil from the roots. Use a serrated blade to cut them into segments with roots and leaves. Plant the new divisions in your desired garden spots, keeping them well-watered until established.
Popular Varieties
While ‘Storm Cloud’ is arguably the best of the species, other Amsonia selections benefit the garden. Here are a few additional species and cultivars with good landscape performance.
‘Hubricht’s Narrow Leaf’
Delicate foliage and steel blue blooms make this perennial standout.
A. hubrichtii is a favorite with delicate, threadlike foliage on upright stems. The leaves are the narrowest among the genus. Considered another “best of,” the species earned the Perennial Plant Association’s Plant of the Year designation in 2011.
These natives grow three feet tall and slowly spread to a whopping six feet wide. In April and May, the full, lacy clumps produce clouds of steel blue flowers. In fall, the foliage turns bright golden orange for a spray of color.
Leslie Hubricht, a naturalist, discovered the species in the Ouachita Mountains of Arkansas in 1942. They occur naturally in fields, rocky outcrops, and creek banks. They’re hardy in zones 5-8.
‘Blue Ice’
Deep lavender-blue blooms and compact size make it stunning.
A. orientalis ‘Blue Ice’ is a selection of a species native to Turkey and Greece. It grows only 15 to 18 inches tall and bears a profusion of large clusters of deep lavender-blue florets in early spring.
One of the showiest bloomers, the origin of the cultivar is muddled. Nurseryman Michael Dodge found it growing on a seed table among tabernaemontana at White Flower Farm in Connecticut. Its origin appears to be orientalis.
‘Blue Ice’ spreads two feet wide. It’s hardy in zones 4-9.
‘String Theory’
Compact and gold in autumn, this variety stays fresh.
‘String Theory’ is a compact version of A. hubrichtii. The variety flowers later than ‘Storm Cloud,’ in late spring/early summer. Plants spread less than the species at 32-36 inches wide and reach 18-22 inches tall.
Feathery leaves stay fresh and green throughout the growing season without yellowing. In autumn, they turn signature deep gold.
‘String Theory’ is protected under a plant patent, and propagation is prohibited.
Common Problems
These carefree growers are free of most pests and diseases. Rust is occasionally a problem among the species. The best prevention is ensuring proper cultural conditions through even watering, sunlight, and healthy soils.
Rust
Increase air circulation and remove infected leaves to prevent rust.
Rust is a common fungal disease, especially in hot and humid climates. Coleosporum rusts sometimes affect the genus. Leaves may yellow, wilt, and drop early.
With rust, you may see leaf spots and powdery spores on the undersides of yellowing leaves. Rust spreads easily, so remove any infected leaves or stems and discard them in a garbage bag or burn pile.
Horticultural oils like neem can treat fungal diseases early on. Cutting back stems to the ground and checking fresh growth or removal is the best action for severely impacted plants in decline.
The best way to prevent rust is to increase air circulation between plants, especially in humid conditions. Watering at the base of the plant delivers moisture to the roots without splashing foliage or harboring damp conditions.
Frequently Asked Questions
This native selection spreads 42 inches wide and reaches two to three feet tall. Its mounding, bushy, upright form makes it a fun shrub alternative and a full addition to the perennial border. It is not aggressive or invasive.
As herbaceous perennials, the species dies back in cold temperatures. Stems and leaves dry and brown with frost. Cut stems off to tidy the look, or leave them in place for added winter protection. Remove them before new spring growth emerges. To refresh growth, cut plants back one-third to one-half in early summer after flowering.
Due to a slightly toxic sap, deer seldom damage these hardy growers, and pests usually leave them alone, too.
