How Long Does a Giant Hyssop Live?

Life Span

• As perennials, giant hyssop plants generally live more than one year, but often die off after two or three years, especially when conditions are not ideal. Traditionally, growers harvested hyssop seedlings for medicinal and herbal use two years after transplanting. Reaching 18 inches in height, the Sonoran Sunset agastache lives just two to three years. Black Adder agastache and Mexican Giant hyssop can grow as high as 36 inches, but will also die off within a few years.

Extending the Life Span

• Protect hyssop under shade and adjust soil moisture to improve life span and blooming. Even under ideal conditions, short-lived perennials such as giant hyssop may live just a few years. They may need replanting after they die off if they do not self-sow on their own. After flowering through the summer, seeds ripen in September and often reseed, reappearing the following season after the original plant dies off.

Drought Tolerance

• Giant hyssop plants are generally moderately drought-tolerant, but should be protected from excess moisture or harsh sunlight. Many varieties of agastache tolerate low precipitation, including Black Adder and Sonoran Sunset varieties. Horsemint, or nettleleaf giant hyssop, on the other hand, is not drought-tolerant and needs moist soils to thrive. Horsemint grows as high as 5 feet in the shade and just 1 foot in full sun. In some varieties, intense sun can shorten giant hyssop's life down to one to two years.

Uses

• As a medicinal and herbaceous plant that lives for a number of years and self-propagates, giant hyssop is a smart addition to any garden. People have used giant hyssop as a stimulant, tonic, diaphoretic, expectorant, analgesic and antirheumatic. It has been used for the treatment of ulcers, sore throats, wounds and pain.

  Hyssop adds herbal flavor and color to salads and is often used in cosmetic applications such as herbal bath products.