The belief that all herbs return reliably year after year often confuses new gardeners. An herb is defined as a plant with savory, aromatic, or medicinal properties, typically used in small amounts to enhance flavor or scent. This broad definition encompasses a wide variety of plants whose lifespans are far from uniform. Understanding these inherent growth patterns is the first step in successfully cultivating a productive herb garden.
Understanding the Terminology
In the context of gardening and culinary use, the term herb is a functional one, describing the leafy green parts of a plant used fresh or dried. This is distinct from a botanical definition, which refers to any non-woody plant, regardless of its use. For cultivation purposes, we are concerned with the aromatic foliage, stems, and sometimes flowers.
A perennial plant lives for more than two growing seasons, returning year after year from the same root structure. These plants invest heavily in persistent root systems and storage organs to survive unfavorable conditions, such as winter dormancy. When the weather warms in spring, the plant regrows new stems and leaves from the crown, the point where the stem meets the roots. This long-term strategy allows perennials to flower and set seed repeatedly over their lifetime.
The Spectrum of Herb Life Cycles
Plants are biologically classified into three main groups based on the time it takes to complete their reproductive cycle. This classification explains why some herbs require replanting every year while others remain permanent fixtures.
The shortest life cycle belongs to the annuals, which germinate, grow, flower, produce seed, and die within a single growing season. This strategy ensures the plant allocates maximum energy into seed production before environmental changes occur. Once the plant has successfully reproduced, its biological purpose is complete, leading to death.
A biennial plant requires a two-year cycle to complete this process. During the first year, it focuses entirely on vegetative growth, developing a rosette of leaves and a robust root system to store energy. The plant remains dormant through the colder months, often requiring this period of chilling, known as vernalization, to trigger the next stage. In the second season, the stored energy is used to produce a tall flower stalk, set seed, and then the plant dies.
Perennials live for multiple seasons, using a long-term approach rather than focusing all resources on one massive seed production event. These plants rely on established root systems to draw energy and nutrients. This enables them to survive multiple seasons of dormancy and re-emerge with reliable growth each spring.
Practical Examples for Gardeners
The longevity of a particular herb dictates how a gardener must approach its care and planting schedule. The most widely grown herbs fall neatly into one of the three life cycle categories.
Common annual herbs include basil, cilantro, and dill, which are all typically sown fresh each spring. Basil, a warm-season favorite, is highly sensitive to frost, forcing it to complete its cycle before the first cold snap arrives. Cilantro is a cool-season annual that quickly “bolts,” or goes to seed, as temperatures rise in the summer, effectively ending its harvest period until cooler weather returns.
Biennial herbs are less common, but parsley is the most recognizable example, often grown for its leaves in its first year and then discarded. If left in the garden, parsley will survive the winter and then produce a tall flower stalk, set seed, and die in its second year. Other biennials include caraway and clary sage, which both require that first year of energy storage before they can successfully flower.
The longest-lived herbs are the perennials, which form the backbone of a permanent herb garden. These include mint, thyme, oregano, and lavender, all of which will return for several years. Rosemary is a popular perennial herb that thrives in warm climates, but it must be grown as a tender annual or brought indoors for the winter in colder regions because it cannot survive a hard frost. Chives are also reliable perennials, returning each year from a small bulb and providing a mild onion flavor from their hollow, grass-like leaves.