The appearance of an overgrown hydrangea can be surprising, often because the plant was small when purchased, or the gardener did not anticipate its mature dimensions. Many popular Hydrangea species can easily reach heights and widths exceeding six feet, making them feel too large for their initial planting location. Nearly all overgrown hydrangeas can be managed without sacrificing the plant’s health or its ability to flower. Safely controlling the size of a large hydrangea requires a strategy based on the specific type of plant to ensure future bloom production.
Diagnosing the Overgrown Hydrangea
Successful size management starts with correctly identifying the species, as this dictates the proper pruning window. Hydrangeas are categorized by where they form their flower buds: on “old wood” (stems from the previous season) or “new wood” (stems grown in the current season). Pruning an old wood bloomer at the wrong time removes the flower buds, resulting in a year without flowers. Old wood bloomers include Bigleaf (H. macrophylla), Mountain (H. serrata), and Oakleaf (H. quercifolia) hydrangeas, which set their buds in late summer and fall.
New wood bloomers, such as Panicle (H. paniculata) and Smooth (H. arborescens) hydrangeas, develop their flower buds on the growth that emerges in spring. These types are more forgiving of aggressive pruning because the new growth will still produce flowers later in the same season. The perception of a plant being too large is often caused by improper placement, such as planting a variety that naturally grows eight feet tall in a space meant for a three-foot shrub. This misplacement forces the gardener into an annual pruning cycle.
Pruning Techniques for Size Reduction
The approach to pruning an overgrown hydrangea for size reduction must be tailored to its blooming habit. For hydrangeas that flower on old wood, like the common mophead and lacecap varieties, hard pruning should be avoided except in cases of severe overgrowth. The best method for managing their size is thinning, which should be performed immediately after the plant finishes blooming in the summer. Thinning involves cutting one-third of the oldest, thickest canes down to the ground to encourage new growth from the base.
This systematic removal of old wood over three years will gradually reduce the plant’s overall size and density while preserving the majority of the flower buds for the next season. If the shrub is drastically overgrown, a one-time, significant cutback may be necessary, but this will almost certainly eliminate the next season’s blooms. Conversely, new wood bloomers, including Hydrangea paniculata and Hydrangea arborescens, can tolerate and benefit from harder pruning.
These varieties should be pruned back in late winter or early spring while the plant is dormant, before new growth begins. For significant size reduction, stems can be cut back by one-third to one-half of their total mass, or even cut down to just 12 to 18 inches above the ground in a process known as rejuvenation pruning. This aggressive pruning promotes the production of new stems that will reliably bear flowers later that summer. This hard cutback is the most effective way to control height and spread without sacrificing the current year’s flowering potential.
Relocation and Prevention Strategies
When annual pruning is insufficient to keep a mature hydrangea in check, moving the plant to a more appropriate location becomes the best long-term solution. The ideal time to transplant a large shrub is when it is dormant, typically in early spring before the leaves emerge or in the fall after the foliage has dropped. Transplanting during dormancy minimizes shock because the plant is not actively pushing out new growth or flowers. Preparation involves digging a new hole that is twice as wide as the root ball and no deeper than the original planting depth.
To lift the plant, a circular trench should be dug just outside the drip line to capture as much of the root system as possible. For a large, mature specimen, the root ball can be heavy and may require wrapping in burlap to keep it intact during the move. After replanting, thorough watering and a two-to-three-inch layer of mulch are necessary to help the hydrangea re-establish itself and reduce transplant stress.
Preventing the problem of an overgrown plant starts with researching the mature size of the specific cultivar before planting it. Many breeders now offer compact or dwarf varieties that remain smaller than their traditional counterparts. For example, instead of a large Hydrangea paniculata that can reach 10 feet, cultivars such as ‘Bobo’ or ‘Little Lime’ top out around three to five feet. Selecting a variety whose mature size matches the space eliminates the need for aggressive pruning and ensures the plant remains a manageable feature in the landscape.