Batten Blooms
PL. —Amsonia tomentosaBotanical illustration — drop image
Amsonia tomentosa

Woolly Bluestar

Spring
5a–9bHardiness zone
Peak bloom windowZone 6b · frost-offset weeks
Winter
Not in bloom
Spring
Peak bloom
Summer
Not in bloom
Fall
Not in bloom
Peak bloom
In bloom
Background

Amsonia tomentosa is a drought-adapted perennial native to arid lowlands of the southwestern United States and the Mexican state of Chihuahua. Dense, woolly hairs coat its stems and leaves, giving the plant a silvery-gray appearance that distinguishes it from other bluestars. Pale blue, star-shaped flowers appear in spring, making it a valuable low-water ornamental for xeric, rock, and native plant gardens.

This species performs best in sharply drained, sandy or gravelly soils with minimal irrigation once established. Consistent moisture or heavy clay soils lead to root rot and weak, sprawling stems. Full sun intensifies the silver quality of the foliage, which holds its appearance through summer. Like all Amsonia, the stems exude a milky sap containing irritating alkaloids; wear gloves when cutting back. It tolerates lean, alkaline soils common to its native range and does not benefit from fertilization.

Good companions
SweetspireMountain MintsAstersWild Geraniums
Care guide
SunFull sun
WaterLow
SoilWell-drained, sandy, rocky, alkaline tolerant
Spacing18–24 in
Height12–24 in
Zone5a – 9b
Native RegionAZ, CA, NV, NM, TX, UT
Frost hardy
Seasonal tasks
spring
watchPale blue flowers open in loose terminal clusters for 3–4 weeks in mid-spring. No deadheading is needed; seedpods that follow are ornamental.
watchCheck drainage after prolonged spring rains. Soil that stays wet for more than a day or two risks crown and root rot; relocate or raise the planting bed if needed.
cutCut stems to ground level in late winter before new growth emerges. Stems left standing through winter provide modest structure and allow any dropped seeds to settle.
sowPlant nursery transplants in sharply drained, gritty soil at or just after the last frost date. Do not amend with compost; lean soil encourages compact, sturdy growth.
cutIf stems become leggy after flowering, cut back by one-third to tighten the plant's form. Wear gloves — the sap is a skin irritant.
summer
watchCollect ripe seedpods before they split open in early fall. Sow seeds immediately outdoors to allow natural winter stratification for spring germination.
watchEstablished plants in their native dry conditions need no supplemental irrigation through summer. Water only if the plant wilts during extreme heat and no rain has fallen for several weeks.
Common problems

Phytophthora Root Rot

Symptoms

Wilting despite moist soil, yellowing leaves, stunted growth, and dark, decayed roots and crown tissue. Vines may collapse during hot weather.

Treatment

Plant in well-draining soil and avoid waterlogging. Remove and destroy affected vines. Improve drainage with raised beds or amended soil and avoid overwatering.

Rust

Symptoms

Orange to brown raised pustules on the undersides of leaves, with yellow spotting on the upper surface. Heavy infections cause leaves to yellow and drop.

Treatment

Remove and destroy infected leaves. Avoid overhead watering and improve air circulation. Apply a sulfur or copper-based fungicide if it spreads. Clear plant debris in fall.