The herb known as Rue, or Ruta graveolens, is correctly classified as a perennial plant. Valued for its distinctive, strong aroma and ornamental blue-green foliage, this species has been cultivated for centuries. It possesses a life cycle that extends beyond two growing seasons, which is the defining characteristic of a perennial. Rue’s robust nature allows it to persist year after year in favorable conditions.
Defining Rue as a Perennial Subshrub
Rue is technically defined as a subshrub, a classification that distinguishes it from purely herbaceous perennials and fully woody shrubs. Since Ruta graveolens lives for more than two years, it fits the perennial description, often reaching a lifespan of around five years or longer in ideal conditions.
The subshrub designation means the plant develops woody stems at its base that persist through the winter. The growth higher up the plant is softer and more herbaceous, and this upper portion may die back seasonally. This semi-woody structure allows the plant to maintain a permanent foundation while regenerating fresh growth from the base each spring.
Climate and Hardiness Zones
Rue’s perennial nature is most reliably expressed in climates similar to its native Mediterranean region, characterized by hot, dry summers. It demonstrates a high tolerance for heat and drought once established. This resilience allows it to thrive in less fertile, well-drained soils.
In North America, Ruta graveolens is perennial within USDA Hardiness Zones 4 through 10. The woody base of the plant can tolerate typical winter temperatures and consistently regrow, being hardy to approximately -10°C.
Gardeners in colder areas, such as Zone 4, often need to provide a protective layer of winter mulch to insulate the crown and roots. When grown outside its typical range, Rue is often treated as an annual, as sustained deep freezes destroy the woody base. In warmer regions, the plant may remain evergreen throughout the year.
Physical Characteristics and Growth Habit
Rue typically grows in an upright, mounding habit, reaching a mature height and spread of between two and three feet. The visual appeal lies primarily in its distinctive blue-green foliage, which is deeply lobed and has a lacy, fern-like appearance. Small, dull yellow flowers appear in clusters above the foliage, usually in the early to mid-summer.
The plant’s subshrub habit necessitates specific maintenance to prevent it from becoming overly woody or leggy over time. Gardeners should cut back the stems to the older, woody growth in early spring before the season’s new growth begins. This pruning action encourages a bushier, more compact shape.
The stems of new growth are soft and green, but they transition to a woody structure as they age. The woody base maintains the plant’s structure, while the softer new shoots are responsible for the seasonal display of foliage and flowers.