A terrific newcomer to American gardens is a Southwest native, Agastache rupestris, also known as sunset hyssop. This drought-tolerant subshrub is worth growing for its vivid color alone, but the best surprise has been the plant's hardiness and adaptability. It flourishes in climates as diverse as the Oregon coast, southern California, northern Colorado, eastern Iowa, Philadelphia, upstate New York, and (judging by a success report from Vienna) Austria. These regions include USDA Plant Hardiness Zones 4b to 9, and a plethora of soil conditions, humidity levels, and temperature extremes.
As summer heat sets in, the plant expands into a dense, twiggy 2-foot-tall by 1½-foot-wide shrub with licorice-scented gray-green foliage. By late summer, it sends up a profusion of flower spikes densely covered in soft orange tubular flowers with mauve-purple calyxes, giving the sunset hues for which the plant is named. Hummingbirds and hawkmoths relish the nectar-rich flowers. Bloom continues for up to two months, until brought to an abrupt halt by hard frost.
Sunset hyssop prefers a hot, sunny spot in well-drained, mineral-rich, humus-poor soil. Cut the fine-textured, somewhat brittle stems down close to the ground at the beginning of the growing season, even if much of the wood remains live, as it does in warmer zones. This radical pruning promotes sturdier, more vigorous growth.
Sunset hyssop is short-lived in damp, cool climates and resents moist winter soil. Otherwise it appears to adapt to most garden situations as long as it has full sun. Its warm colors and full, bushy texture combine well with late-season grasses such as Mexican feather grass (Stipa tenuissima, syn. Nassella tenuissima) and the taller big sacaton (Sporobolus wrightii), two other lovely Southwest natives. Late- blooming, similarly drought- tolerant plants such as blue mist spirea (Caryopteris X clandonensis), Russian sage (Perovskia spp. and hybrids), and Maximilian sunflower (Helianthus maximiliani) also make good companions. This recently discovered treasure offers lively color and delicious fragrance, while bringing wildlife into our late-season gardens.