A shrub is a perennial woody plant commonly seen in both natural landscapes and cultivated gardens. Broadly defined, a shrub maintains a persistent structure above the ground throughout the year, even during dormancy. This woody characteristic distinguishes it from plants that completely die back to the soil surface each season.
Defining Physical Characteristics
The defining feature of a shrub is its woody nature, meaning its stems are durable and persistent rather than soft and herbaceous. These stems survive the winter, allowing the plant to resume growth from existing structures in the spring. This creates a permanent framework that contributes to the plant’s overall form.
The growth pattern typically involves multiple stems arising from or near the base. This basal branching gives the plant a dense, bushy appearance, as there is no single, dominant trunk. While height is variable, shrubs generally remain under 20 feet (6 meters) tall, with some definitions setting the upper limit at around 10 feet.
How Shrubs Differ from Trees
The primary distinction between a shrub and a tree lies in their structural architecture, even though both are perennial and woody. Trees are generally characterized by having a single, dominant stem, known as a trunk or bole, which supports a crown of branches significantly clear of the ground. In contrast, a shrub’s energy is distributed into multiple stems that begin branching close to the soil line, resulting in a more spreading, non-dominant form.
While size is often cited, it is a secondary characteristic to the growth habit. Trees are typically taller, often exceeding 20 feet at maturity, while shrubs rarely reach this height. The presence of a clear, single trunk defines the tree form, whereas the dense, multi-stemmed structure defines the shrub form.
Shrubs Versus Perennial and Subshrub Plants
Shrubs are clearly differentiated from herbaceous perennial plants by the presence of persistent, woody tissue. Herbaceous perennials possess soft, non-woody stems that typically die back completely to the root system each year in colder climates. Shrubs, whether deciduous or evergreen, maintain their woody stems above ground through the dormant season.
The distinction becomes more subtle when comparing shrubs to subshrubs, also known as dwarf shrubs or semi-woody plants. Subshrubs are small, low-growing plants that have a woody base, but their upper growth consists of softer, more herbaceous stems that may die back seasonally. For example, plants like lavender or thyme are often classified as subshrubs because their top growth is short-lived and non-woody. A true shrub maintains woody tissue from the root crown to the branch tips. Subshrubs are typically less than three feet tall and represent the lower, less-woody end of the shrub spectrum.