Agastache, commonly known as Anise Hyssop or Hummingbird Mint, is a genus of aromatic plants celebrated for their attractive, spiky blooms and fragrant foliage. These plants, members of the mint family, produce upright flower spikes that draw in hummingbirds, bees, and butterflies, making them a popular garden choice. Their leaves often release scents reminiscent of anise, licorice, or mint when crushed. The question of whether Agastache is a perennial is not straightforward, as the answer depends heavily on the specific plant variety and the geographic location where it is grown.
Understanding the Perennial Nature of Agastache
Agastache is a large genus whose classification as a perennial, annual, or tender perennial depends entirely on the local climate. A true perennial reliably returns year after year, with its root system surviving the winter dormant season. Many Agastache varieties are considered “tender perennials,” meaning they can survive multiple years only in mild climates.
In colder regions, these plants are often grown as annuals, completing their life cycle in a single growing season and dying back with the first hard frost. The primary factor determining a plant’s ability to survive the winter is the minimum temperature it can tolerate. This threshold is mapped out by the United States Department of Agriculture (USDA) Hardiness Zones. For Agastache to survive as a perennial, the winter low temperatures must not drop below the minimum threshold for that specific species. Root survival is the critical point for many varieties, which is greatly challenged by freezing temperatures combined with wet soil.
Key Species and Their Hardiness Ratings
The hardiness of Agastache varies widely between species and hybrid cultivars, with some being significantly more cold-tolerant than others. Agastache foeniculum, known as Anise Hyssop, is one of the most reliably hardy types. This species is native to the prairies of North America and is capable of surviving in USDA Zones 4 through 8, or sometimes even Zone 3 in favorable conditions. It is notably more tolerant of cold and winter moisture than many of its relatives.
Agastache rupestris, or Licorice Mint Hyssop, is another popular species known for its sunset-orange flowers and preference for dry conditions, thriving in Zones 5 to 9. Many newer, brightly colored hybrids, such as those derived from Mexican Hyssop (Agastache mexicana), are commonly treated as annuals in most of North America. These varieties often have a limited perennial range, typically surviving only in Zones 6 or 7 and warmer. The key distinction for these Southwest-native varieties is the requirement for excellent drainage to survive winter cold.
Essential Care for Overwintering Survival
For gardeners at the colder edge of a variety’s hardiness range, proper preparation is necessary to ensure the plant returns the following spring. The single most important factor for winter survival is sharp soil drainage. The roots of most Agastache species are highly susceptible to rot if they sit in cold, saturated soil. Planting in a location where water does not collect is crucial, and amending the soil with grit or sand before planting can greatly improve the odds of overwintering.
It is recommended to delay pruning the plant until new growth begins in the spring. Leaving the old, spent stems standing through the winter provides a natural layer of insulation for the plant’s crown, protecting the dormant growth point from harsh cold. In marginal zones, a light, protective layer of coarse mulch, such as shredded leaves or straw, can be applied around the base of the plant in late fall after the ground has frozen. Care must be taken to keep the mulch from directly covering the crown, which could trap excessive moisture and lead to rot.