The question of whether all herbs are annuals is common for new gardeners, but the answer is definitively no. The term “herb” broadly applies to plants valued for their medicinal, savory, or aromatic properties. These plants belong to distinct classifications, each with a unique life cycle that determines how long they survive and whether they return each year. Understanding these differences is the foundation for successfully growing and harvesting herbs.
Defining Plant Lifespans
Plants are categorized into three main groups based on the length of time required to complete their full life cycle, from germination to seed production. An annual plant completes this entire cycle within a single growing season and then dies completely, leaving behind only its seeds. Annuals must be replanted every year to ensure a continuous supply.
A perennial plant lives for multiple growing seasons, typically for more than two years. The above-ground growth of many perennials will die back in the winter, but the root system remains alive underground, allowing the plant to regrow reliably in the spring. Biennial plants require two years to complete their cycle. They establish foliage and root systems in the first year, survive the winter, and then flower, set seed, and die in the second year.
Common Herbs That Are True Annuals
True annual herbs complete their mission of producing seeds before the season ends. Basil (Ocimum basilicum) is a primary example, as it grows rapidly and is highly sensitive to cold temperatures. If the flowers are not consistently pinched off, the plant will “bolt,” or send up a seed stalk. This causes the flavor and texture of its leaves to decline as the plant shifts its energy to reproduction.
Dill (Anethum graveolens) follows a strictly annual cycle, germinating, growing, flowering, and setting seed all within one season. Cilantro (Coriandrum sativum), which produces the spice coriander from its seeds, also behaves as a true annual. These quick-maturing herbs are often succession-planted, meaning new seeds are sown every few weeks throughout the growing season to ensure a continuous harvest.
Perennial and Biennial Herb Varieties
A large group of popular herbs are perennials, returning reliably year after year from the same root structure. Herbs like mint (Mentha spp.), thyme (Thymus vulgaris), oregano (Origanum vulgare), and lavender (Lavandula) are perennials because their root systems are built to survive cold, dormant periods. These plants often require less frequent watering and fertilization than annuals. They benefit from occasional pruning to encourage fresh, flavorful growth and prevent them from becoming woody or sprawling.
Parsley (Petroselinum crispum) is a prime example of a biennial herb, though it is often treated as an annual in culinary gardens. In its first year, parsley produces the abundant, flavorful leaves used for cooking. If it survives the winter, the plant will send up a tall flower stalk in the second year, shifting its energy away from leaf production. This causes the foliage to become coarse and bitter before the plant dies.
How Climate Affects Herb Longevity
The botanical classification of a plant does not always align with how a gardener grows it, which is often the source of confusion regarding herb life cycles. Many herbs are botanically perennials but are intolerant of cold winter temperatures, forcing gardeners to treat them as annuals. This distinction is governed by the plant’s hardiness zone, a geographical area defined by its minimum average winter temperature.
Rosemary (Salvia rosmarinus) and Bay Laurel (Laurus nobilis) are examples of woody, evergreen perennial herbs that thrive in warmer climates, typically USDA zones 8 and higher. In regions with significant winter frost, these plants cannot survive outdoors year-round and will perish if left in the ground. Gardeners in colder zones must either replant them annually or grow them in containers that can be moved indoors during the winter months to protect the roots.