The question of whether a holly is a bush or a tree is a common source of confusion for gardeners and homeowners. This uncertainty arises because the genus Ilex, which encompasses over 400 species of woody plants, is remarkably diverse. Within this single group, forms range from low-growing groundcovers to a wide variety of towering specimens. The difference between a holly acting as a bush and one acting as a tree often depends on the specific variety and how it is managed.
The Direct Answer: Holly’s Dual Identity
Holly is botanically classified as both a shrub and a tree, depending entirely on the species and environmental factors. The genus Ilex includes species that naturally develop into massive, single-trunked trees, as well as others that remain small, multi-stemmed shrubs. It is impossible to give a blanket classification to all plants in this group. Knowing the specific variety is the only way to accurately determine its natural growth habit.
Some hollies possess the genetic potential to reach heights of over 40 feet, placing them in the tree category. Conversely, many popular landscaping hollies are genetically predisposed to stay under 15 feet and maintain a bushy, rounded form. The distinction lies within the plant’s DNA, but it is also heavily influenced by the growing environment.
Defining the Difference Between Shrub and Tree
The distinction between a shrub and a tree is based on two primary characteristics: ultimate height and structural form. While there is no universal botanical cutoff, trees are generally defined as perennial woody plants that exceed 20 feet in height at maturity. They typically feature a single, dominant main stem, or trunk, that supports a distinct crown of foliage above the ground.
Shrubs are smaller woody plants that rarely surpass 20 feet in height. Their defining structural feature is the presence of multiple woody stems that arise from the base of the plant, often branching close to the ground. This multi-stemmed habit gives shrubs their characteristic dense, bushy appearance.
Species Variation and Natural Growth Habit
Specific holly species illustrate this divide, with some varieties naturally growing as trees and others as shrubs. American Holly (Ilex opaca) is a prime example of a true tree-form holly, often reaching 40 to 60 feet tall in its native habitat with a distinct, pyramidal shape. English Holly (Ilex aquifolium) is also an upright broadleaf evergreen that can grow to 30 to 50 feet with a dense, tree-like habit.
On the shrub side, varieties like Japanese Holly (Ilex crenata) typically grow as a dense, multi-stemmed shrub between 6 and 10 feet tall. Inkberry Holly (Ilex glabra) is another native shrub-form holly, known for its multiple, slender stems and maximum height of 5 to 8 feet. The natural, untrimmed growth pattern of these species dictates their classification.
Influencing Form Through Cultivation
Regardless of a holly’s natural tendency, human intervention through cultivation can drastically alter its final form. A naturally tree-form holly, such as American Holly, can be heavily pruned and sheared into a dense, multi-stemmed hedge that functions as a shrub or bush. This aggressive pruning prevents the plant from developing a single dominant trunk.
Conversely, horticulturists can train a naturally shrub-form holly into a small, single-trunked specimen called a “standard.” This is achieved by systematically removing all but one central stem and continually pruning the lower side branches to maintain a clear trunk. These training techniques demonstrate that while genetics set a plant’s potential, careful pruning ultimately determines its landscape role as either a bush or a tree.