Coleus is botanically classified as a tender perennial, meaning it lives for more than two years but cannot tolerate cold temperatures. The species most commonly cultivated, Coleus scutellarioides, is native to tropical and subtropical regions of Southeast Asia and Australia, where it naturally grows year-round as a perennial. However, most gardeners in temperate climates treat Coleus as an annual, replanting it each spring because it cannot survive the winter cold. This dual classification results from the plant’s sensitivity to frost and cold weather.
The Botanical Classification of Coleus
Understanding typical plant life cycles provides context for Coleus’s classification. An annual plant completes its entire life cycle within a single growing season. Conversely, a perennial plant lives for more than two years, often growing back from the roots or a woody base each spring. Coleus is considered a tender perennial because it is perennial in its native tropical habitat but lacks the hardiness to survive freezing temperatures.
The natural habitat of Coleus scutellarioides is characterized by consistently warm temperatures and high humidity. In these tropical regions, the plant is a bushy, woody-based evergreen that flowers and fruits throughout the year, demonstrating a perennial growth habit. Its classification as a perennial is based on its genetic potential to live for multiple years when not subjected to cold stress.
Why Coleus is Treated as an Annual
Coleus is grown as an annual primarily because of its intolerance for freezing temperatures. It is typically winter hardy only in USDA Hardiness Zones 10 and 11, where temperatures rarely dip below 40°F. Outside of these warmest zones, such as parts of South Florida and California, the plant cannot survive the winter outdoors.
Gardeners in temperate regions must treat Coleus as an annual because the plant’s succulent, herbaceous stems are highly susceptible to frost damage. When the temperature drops below freezing, the water within the plant’s cells freezes and expands, rupturing the cell walls. This physiological damage causes the foliage and stems to shrivel and collapse into a mushy state. Because the entire plant dies back and cannot regenerate from the roots after a cold winter, it must be replanted from seed or new stock each spring.
Methods for Keeping Coleus Year-Round
Gardeners who wish to retain a specific Coleus variety beyond a single season must intervene to protect it from the cold. One common method is to overwinter the entire plant indoors by potting it up and bringing it inside before the first frost, ideally when nighttime temperatures consistently fall below 50°F. Once indoors, the plant requires bright light, such as a south- or southeast-facing window, and a room temperature consistently above 60°F. Watering should be reduced during the winter months, allowing the top inch or two of soil to dry out between waterings, as the plant’s growth slows significantly.
A second, more space-efficient strategy is to propagate new plants from cuttings taken in the fall. This involves clipping three- to four-inch stem tips from the healthy parent plant before cold weather arrives. These cuttings can be rooted easily in either a small container of moist potting mix or simply a glass of water, with roots often developing within a couple of weeks. The newly rooted cuttings are then grown as small houseplants throughout the winter, providing ready-to-plant stock to transplant back into the garden once the danger of frost has passed in the spring.