A shrub is a woody, perennial plant that is smaller than a tree and possesses a distinct growth habit. These plants form a foundational component of both natural ecosystems and cultivated green spaces worldwide. They are defined by persistent, above-ground woody stems that survive over multiple seasons, unlike non-woody plants. Shrubs contribute significantly to the structure of forests, deserts, and gardens, serving various roles from ground cover to middle-layer vegetation.
Core Characteristics and Structure
The defining feature of a shrub is its multi-stemmed structure, where multiple woody shoots arise from or very close to the base of the plant. This contrasts with the single, dominant trunk that characterizes most trees. This growth habit results in a bushy, dense appearance, often lacking a clear main stem.
Shrubs maintain a height that is less than 20 feet (6 meters) at maturity, though many species stop growing around 10 feet (3 meters) tall. The stems are composed of hard, lignified tissue, which provides structural support and allows the plant to persist through various weather conditions. Small shrubs under 6.6 feet (2 meters) in height are sometimes termed subshrubs.
Distinguishing Shrubs from Trees and Herbs
The primary difference between a shrub and a tree lies in the stem structure and maximum height. Trees have a single, thick, woody trunk that is typically unbranched for a distance above the ground, forming a distinct crown. Shrubs, however, branch profusely from the soil line, creating a multitude of stems of similar diameter.
While some large shrubs can approach the size of small trees, a mature tree exceeds the 20-foot height threshold. Shrubs are also distinct from herbaceous plants, which include garden flowers and grasses. Herbaceous plants have soft, green, non-woody stems that often die back to the ground each year, whereas a shrub’s woody stems are permanent and persistent.
Growth Cycles and Leaf Retention
Shrubs are categorized based on their foliage retention throughout the annual growth cycle. Deciduous shrubs shed all of their leaves seasonally, usually in autumn, in response to decreasing daylight and colder temperatures. This leaf drop is a survival mechanism that reduces water loss during the dormant period. Examples of deciduous shrubs include lilacs and many types of roses.
Conversely, evergreen shrubs retain their green foliage throughout the year, with leaves persisting for more than one growing season. While they shed older leaves, this process is gradual and not tied to a single season, meaning the plant always appears green. Holly and rhododendrons are common examples of evergreen shrubs. Some species, known as semi-evergreen, may only lose their leaves in colder climates or during periods of extreme drought.
Common Roles in the Landscape
Shrubs serve numerous practical functions in human-managed environments, extending beyond simple ornamentation. They are frequently planted in rows to create hedges, acting as living barriers to define property lines or provide privacy screening. The dense, multi-stemmed form makes them ideal for creating solid, vertical walls in a garden design.
Many shrubs are used as foundation plantings, positioned near buildings to soften the structure’s hard lines and transition the architecture to the surrounding landscape. Their dense root systems also play a role in environmental conservation by stabilizing soil and controlling erosion on slopes. Furthermore, shrubs are important for local biodiversity, offering shelter, nesting sites, and food sources like berries and nectar for birds, insects, and other small animals.