The vast majority of plants commonly identified as lilies, which belong to the genus Lilium, are classified as perennials. True lilies are herbaceous, bulb-based species that return to bloom year after year. They are not annuals, meaning they do not complete their entire life cycle in a single growing season before dying off. This longevity is tied to their underground storage structure, which allows them to survive dormant periods and regrow reliably.
Understanding Annuals and Perennials
Annual plants have the shortest lifespan, completing their entire life cycle—germinating, growing, flowering, and setting seed—within one single growing season. Gardeners often use these plants for seasonal color because their existence is contained within a few months.
Biennial plants require two full growing seasons to complete their life cycle. In the first year, a biennial develops its root system, stems, and leaves, often storing energy in a root or bulb. During the second year, the plant flowers, produces seeds, and then dies.
Perennial plants live for more than two years, often for many seasons or decades. They survive periods of cold or drought by going dormant, allowing them to return from the same root structure or crown in subsequent years. This difference separates a long-term garden fixture from a short-lived seasonal planting.
The Perennial Life Cycle of True Lilies
True lilies, classified under the genus Lilium, are classic examples of herbaceous perennials due to their specialized survival mechanism. They develop from a fleshy, scaly underground bulb that serves as a storage organ for carbohydrates and nutrients. The bulb enables the plant to enter winter dormancy in cold climates, protecting the living tissue from freezing temperatures.
During the spring and summer, the plant uses the stored energy in the bulb to send up a new stem and foliage. This foliage performs photosynthesis to replenish the bulb’s reserves. Lilies thrive in USDA Hardiness Zones 4 through 9, demonstrating tolerance for cold weather. Most true lilies are deciduous, meaning their above-ground foliage naturally dies back in the autumn.
This annual dieback signals the bulb’s transition into its dormant state, resting underground until the spring thaw triggers new growth. Because the bulb remains alive and intact below the soil surface, it can sprout new growth repeatedly each year without needing to be replanted.
Common Plants Mistakenly Called Lilies
Confusion about the true nature of lilies often arises because the word “lily” is included in the common name of many unrelated plants. Botanically, only members of the Lilium genus are true lilies; other plants with “lily” in their name belong to entirely different families. For instance, the popular Daylily (Hemerocallis) is a perennial but belongs to a different family and grows from tuberous roots, not a true bulb.
Other misnamed plants, such as Calla lilies (Zantedeschia) and Canna lilies (Canna), are technically perennial but are often treated as annuals in regions with cold winters. These species originate from warmer climates and lack the necessary cold hardiness to survive a hard frost outdoors. Gardeners in colder zones must dig up and store the rhizomes or tubers of these plants indoors for the winter, or simply treat them as annuals that must be replanted each spring.
Peace lilies (Spathiphyllum) and Water lilies (Nymphaea) are also not true lilies and are classified as tropical or aquatic plants, respectively. Their growth habits and survival strategies are completely distinct from the bulb-based dormancy of the true Lilium species.