Tree shaping, often called arboricultural art, involves intentionally manipulating a woody plant’s growth direction and structure to achieve a specific, non-natural form. This deliberate training utilizes the tree’s natural response to pruning and binding to create aesthetic or functional living sculptures. Rooted in ancient traditions, tree shaping has been used for centuries across diverse cultures to maximize space, increase yield, or create beauty. The success of this art depends on understanding plant biology and selecting species with the necessary growth characteristics for training.
Methods of Intentional Tree Shaping
Topiary
Topiary is the most widely recognized method, involving the frequent, precise shearing of dense-foliaged shrubs and trees into geometric, animal, or abstract sculptural shapes. This technique focuses on maintaining the outer silhouette rather than manipulating the internal branch structure.
Espalier
Espalier is a method of training a tree to grow flat against a surface, such as a wall, fence, or trellis, creating a two-dimensional design. This process typically involves severe pruning of the central leader and tying flexible young branches to a support structure to encourage horizontal growth. Fruit trees, particularly apple and pear, are traditional subjects because this method allows sunlight to reach more fruit and is efficient for small spaces.
Pleaching
Pleaching is a technique where the branches of multiple trees planted in a line are interwoven and tied together to form a continuous, dense hedge or elevated screen. Unlike standard hedging, pleaching relies on the branches of adjacent plants fusing together, or inosculating, to create a single, living architectural wall. This is a common choice for creating formal borders or elevated screening in European gardens.
Pollarding
Pollarding represents a structural and size-controlling method where the upper branches of a tree are removed back to a specific point on the trunk or main branch framework, forming a characteristic swelling called a pollard head. This severe annual or biennial pruning stimulates a dense flush of thin, new shoots from the cut points, keeping the tree permanently contained at a set height. Historically, pollarding was used to harvest wood or fodder out of the reach of grazing animals, and today it is often used for urban street trees.
Characteristics of Ideal Trees for Training
Trees suitable for shaping must have a high tolerance for heavy pruning, as techniques like topiary and pollarding remove significant vegetative growth. This resilience allows the tree to rapidly produce new shoots from adventitious buds after a cut, a process known as vigorous re-sprouting.
Trees with a dense growth habit and small leaf size are favored for topiary, as they create a smooth, tightly manicured surface without revealing the underlying structure. Broadleaf evergreens such as Boxwood (Buxus sempervirens) and certain varieties of Holly (Ilex) are popular choices due to their persistent foliage and ability to form a thick canopy. Conifers like Yew (Taxus) and Juniper (Juniperus) are also excellent for sculpted forms because of their fine, scale-like needles and slow growth rate.
For methods requiring branch manipulation, like espalier and pleaching, the tree must exhibit flexible wood, especially in young growth. Fruit trees such as apple (Malus) and pear (Pyrus) are traditional choices for espalier because their branches are soft and pliable enough to be tied to wires or frames without snapping. Deciduous trees like Linden (Tilia) are often used for pleaching due to their ability to produce long, straight shoots that readily interweave and their willingness to fuse where their bark touches. Selecting a species with a naturally manageable or slow growth rate also reduces the frequency of necessary maintenance cuts, making the sculpted form easier to sustain over time.
Essential Tools and Timing for Initial Shaping
Establishing the initial structure requires specific tools for clean cuts and materials for securing the growth pattern. Handheld bypass pruners are used for small, precise cuts on young shoots. For thicker branches, loppers provide increased leverage for cuts up to two inches, while specialized pruning saws remove larger structural wood.
Support materials, such as heavy-gauge wire, durable twine, and sturdy trellises, are essential for fixing branches in their desired position during shaping. The initial structural cuts must be made with sterilized tools to prevent the introduction of pathogens, especially when working on species prone to disease. Wiping blades with an alcohol solution or bleach mixture between plants helps to reduce the risk of transmission.
The timing of the initial structural cut depends heavily on the tree type and the local climate. For deciduous trees, such as those used in pollarding or espalier, the dormant season—late fall through early spring—is preferred. Pruning during dormancy minimizes sap loss, or “bleeding,” and allows the tree to use stored energy for healing and new growth once the active season begins. Evergreens are often pruned lightly during the active growing season to immediately see the effect of the shape and prevent large, unsightly wounds.
Maintaining Established Tree Shapes
Once a tree’s desired form is established, ongoing maintenance prevents the plant from reverting to its natural growth habit. The frequency of trimming is higher than for standard ornamental pruning, often requiring several light trims throughout the growing season. For formal topiary, regular shearing is performed as soon as new growth begins to compromise the clean lines of the sculpture.
Techniques are employed to manage the plant’s vigor, particularly in restricted forms like espalier or bonsai. Root pruning, where a portion of the tree’s root system is intentionally removed, is sometimes performed to slow the top growth and keep the plant in proportion with its restricted size. This process reduces the plant’s capacity to take up water and nutrients, thereby limiting the energy available for shoot extension.
Careful monitoring is required to look for signs of structural failure or disease, which can be concentrated around the areas of repeated cuts. Since shaping involves creating numerous wounds, the tree is more susceptible to entry by decay fungi or insect pests. Regular inspection of the pollard heads or the wire-bound joints in an espalier ensures that structural supports are not girdling the expanding bark and that wounds are healing cleanly over the cuts.