Sunset hyssop is a perennial of the mint family (Lamiaceae), growing to about 100cm tall, with silvery-green, narrow leaves of a soft texture, giving it another common name, threadleaf giant hyssop. Its foliage has a liquorice, slightly minty scent and is said to deter browsing animals. When dormant in winter it has attractive grey-green stems and leaves.

It has pinkish-orange tubular flowers, borne on delicate "ear of wheat" like spikes rising above the foliage. These have contrasting darker red to purple buds that add colour to the display. The flowers appear in midsummer and last into autumn, attracting many insects including bees and butterflies. Deadheading the plant after the initial flowering will often encourage a longer flowering period into the autumn.

Preferring sandy to rocky soils with very good drainage, it is popular in xeriscaping for its heat tolerance and ability to thrive in dry, nutrient-poor soils. It will not survive the winter in wet heavy soils and will develop root rot if it becomes too wet. If in doubt about the soil, plant on a slope or raised area to improve drainage. It will grow up to a metre tall and half as wide, reaching maturity in 2-5 years.