The striking, airy blooms of the Cleome, commonly known as the Spider Flower, are a favorite in garden beds. With its uniquely shaped flowers and long, spidery stamens, the plant adds a dramatic, vertical element to the landscape. Whether this popular feature is an annual or a perennial is a common source of confusion. The classification depends heavily on the local climate and the specific species being grown.
The True Classification of Cleome
The most widely cultivated variety, Cleome hassleriana, is botanically categorized as a tender annual in the vast majority of North American climates. An annual plant is defined by completing its entire life cycle—from germination to seed production to death—within a single growing season. For Cleome, this cycle is terminated by the first hard frost, which kills the parent plant.
The term “tender annual” indicates that the plant is sensitive to cold temperatures and cannot survive through the winter months in temperate zones. Because of this frost intolerance, gardeners in areas experiencing cold winters treat the plant as a single-season bloomer. Its native habitat in South America is much warmer, explaining its inability to withstand freezing temperatures.
However, the classification shifts dramatically in warmer regions where the plant can survive the winter months. In specific warm climates, generally within USDA Hardiness Zones 9 through 11, Cleome hassleriana can function as a true perennial. In these mild environments, the plant does not die back and can continue to grow and bloom for multiple years. This ability to persist year-round is only true under specific, frost-free conditions.
The Mechanism of Return
Despite being an annual in most areas, Cleome often appears to behave like a perennial due to its prolific reproductive strategy. The plant produces numerous elongated seed pods that mature and split open, dispersing many small, viable seeds onto the surrounding soil. This process, known as self-seeding, is the mechanism by which the plant “returns” each spring.
The seeds often require cold stratification or warming soil temperatures to prompt successful germination. These conditions are naturally met when the seeds overwinter in the garden soil and sprout once the weather warms. The new plants that emerge are a new generation of seedlings, often referred to as “volunteers,” not the old parent plant growing back.
This vigorous self-seeding can be a significant advantage for the gardener, as it saves the effort of replanting each year. The new volunteers will appear in the approximate location of the previous season’s growth, creating a continuous presence in the garden. For some older cultivars, self-seeding can be so aggressive that the plant must be managed. This management prevents it from taking over the garden space.
Growing and Maintaining Cleome
To successfully grow Cleome, the plant requires a location that receives full sunlight for the majority of the day. It thrives in average to well-drained soil and exhibits tolerance for heat and drought once its root system is established. While it can handle some dryness, consistent moisture promotes better growth and more abundant flowering throughout the summer season.
The plant’s natural tendency to self-seed can be controlled through a process called deadheading, which involves removing the spent flowers. Deadheading prevents the development of the long, thin seed pods that contain the next generation of seeds. Removing these seed pods before they dry out and shatter significantly limits the number of volunteer seedlings that appear the following year.
Newer, sterile hybrid varieties, such as the ‘Señorita’ series, have been developed that are incapable of producing viable seeds. Gardeners who wish to avoid self-seeding or the need for deadheading should choose these specific cultivars. These hybrids must be purchased as new transplants each spring, as they cannot reproduce themselves in the garden.