Amsonia tharpii is a perennial native to rocky slopes and dry grasslands of New Mexico and Texas. Its common name, feltleaf bluestar, describes the soft, woolly texture of its leaves — an adaptation to intense heat and low rainfall. Pale blue, star-shaped flowers appear in spring on upright stems, consistent with the broader bluestar genus.
It performs best in full sun with sharply drained, sandy or gravelly soil. Once established, it is highly drought-tolerant and needs little supplemental water. Foliage holds up well through hot summers and turns gold in fall, giving it two seasons of ornamental value. Avoid heavy clay and any site prone to standing water, which will kill the plant quickly. It is well suited to xeric, rock, and native plant gardens across the Southwest and lower South.
The milky sap contains indole alkaloids common to the Apocynaceae family, making the plant consistently unpalatable to deer and rabbits. Avoid sap contact with skin or eyes when cutting stems.
Phytophthora Root Rot
Wilting despite moist soil, yellowing leaves, stunted growth, and dark, decayed roots and crown tissue. Vines may collapse during hot weather.
Plant in well-draining soil and avoid waterlogging. Remove and destroy affected vines. Improve drainage with raised beds or amended soil and avoid overwatering.
Powdery mildew
White or grey powdery coating on leaves — usually starting on older growth in humid conditions or when nights cool.
Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.