A member of the Bignoniaceae family, the Catalpa tree (sometimes called the Indian Bean Tree or Cigar Tree) is known for its large leaves and distinct, long, bean-like seed pods. While its tropical appearance is highly desirable, its natural growth habit conflicts with smaller spaces. Catalpas can quickly reach 40 to 60 feet in height with a significant spread, making them too large for many modern gardens. To overcome this size limitation, the tree must undergo a rigorous, repetitive pruning regimen. This guide details the specific techniques required to permanently restrict the natural scale of the Catalpa tree.
Understanding Catalpa’s Natural Growth and Response
Keeping a Catalpa small is challenging due to its fast growth rate and resilience. Catalpas are vigorous growers, adding one to two feet in height annually, and respond to heavy pruning with an explosion of new growth. This response results from disrupting apical dominance, the process where the main terminal bud produces hormones that suppress the growth of lateral buds lower down the stem. Removing the dominant growing tip alters the balance of growth hormones, releasing the inhibited lateral buds, which causes a flush of new, rapid-growing shoots known as epicormic growth or water sprouts. Successfully maintaining a small size relies on exploiting this strong, compensatory growth mechanism.
Aggressive Pruning: Coppicing and Pollarding
To artificially maintain a small stature, the Catalpa must be subjected to two specific forms of aggressive, repetitive pruning: coppicing or pollarding. These techniques are distinct from standard aesthetic pruning and are designed to exploit the tree’s natural tendency to produce vigorous, dense regrowth. The choice between them depends on the desired final form, whether a multi-stemmed shrub or a small tree with a defined trunk.
Coppicing involves cutting all stems down to within a few inches of ground level, resetting the plant. This method encourages numerous new shoots directly from the root crown, forming a bushy, multi-stemmed shrub. It is the simpler method to initiate, requiring only a single, drastic cut, but it must be repeated every few years to prevent stems from maturing into a full tree structure.
Pollarding, by contrast, restricts the tree’s height to a predetermined level by cutting back to a permanent, elevated structure. To begin, the young tree is allowed to grow to the desired trunk height, typically three to five feet from the ground. All lower branches are removed to establish a clear trunk. The main trunk is then topped, and three to five strong, well-spaced lateral branches are selected to form the permanent scaffold.
These selected scaffold branches are cut back hard, leaving stubs, usually no more than four inches long, to establish the pollard head or knuckle. Over subsequent years, new shoots will sprout from this knuckle. Annual pruning repeatedly cuts back to the same point, causing the knuckle to swell and become a characteristic feature. This initial cut is the most important step, as it permanently establishes the maximum height and structural framework.
Year-Round Maintenance and Timing
Once the Catalpa is established through coppicing or pollarding, consistent, cyclical maintenance is required to preserve the restricted size. The timing of this annual cut is important for the tree’s health and the success of the size-restriction effort. All annual pruning should be performed during the dormant season, ideally in late winter or very early spring (late January to March).
Pruning during dormancy minimizes stress and prevents the waste of energy the tree would otherwise invest in new spring growth. Cutting back as the sap begins to rise channels the tree’s energy reserves into forming dense, large-leaved regrowth. For pollarded trees, all previous season’s growth must be cut back to within an inch or two of the established knuckle, cutting slightly above the previous year’s scar.
Consistent pruning prevents new shoots from developing into thick, heavy limbs that could break away from the knuckle. Managing the dense head of regrowth is also necessary; thin out overcrowded new sprouts to ensure adequate air circulation and light penetration. Additionally, any shoots that sprout from the main trunk below the pollard head must be promptly removed to maintain the desired structure.