Hydrangeas are popular flowering shrubs prized for their large, colorful bloom heads and lush foliage. These plants are a common feature in many landscapes, leading gardeners to wonder about their growth habits. Understanding the way hydrangeas naturally expand helps manage them effectively in any yard.
How Hydrangeas Naturally Grow
Most common garden hydrangeas are classified as clumping shrubs, meaning their root systems do not travel great distances. Species like the Bigleaf Hydrangea (Hydrangea macrophylla) and the Panicle Hydrangea (Hydrangea paniculata) primarily expand outward from a central root crown. The plant’s footprint widens slowly over time as new stems emerge close to the original plant. This growth pattern results in a single, defined, and generally manageable shrub that increases in girth rather than sending out runners or rhizomes.
Self-Propagation Mechanisms
While hydrangeas do not typically spread via invasive roots, they can produce new, separate plants through a process called natural layering. This occurs when a flexible, low-lying branch touches the soil surface for an extended period. The branch’s contact point, often a leaf node, may develop adventitious roots, effectively forming a new, independent plant. This secondary plant will grow adjacent to the original shrub, making it appear as though the main plant is spreading.
Natural layering is a common form of self-propagation, particularly in varieties with arching stems that easily reach the ground. Less frequently, hydrangeas can also disperse seeds, though garden varieties are often sterile or their seeds require specific conditions to germinate. Seedlings, if they do appear, usually sprout near the parent plant but are easy to identify and remove if unwanted.
Growth Differences Among Common Species
The spreading tendencies of hydrangeas vary significantly depending on the species planted. The widely grown Bigleaf Hydrangea (H. macrophylla) and Panicle Hydrangea (H. paniculata) are generally the most stable, maintaining their clumping structure. These types primarily expand through canopy growth and the slow outward expansion of the main root ball. The Oakleaf Hydrangea (H. quercifolia), however, exhibits a more vigorous tendency to spread through suckering. Suckers are new shoots that emerge directly from the plant’s root system, often a short distance from the main crown.
Managing Hydrangea Size and Spread
Gardeners can easily control the size and spread of their hydrangeas by understanding the specific growth habits of their plants. For shrubs that propagate through natural layering, the solution is to simply prune the low-lying branches to keep them off the soil surface. If a branch has already rooted, the new plant can be dug up and transplanted, or the connecting stem can be cut to separate it from the mother plant.
Managing the suckering growth of species like the Oakleaf Hydrangea requires a different approach. The suckers should be pruned or cut off at or just below the soil line when they are noticed. Consistent removal of these root shoots prevents the formation of a dense, spreading colony, maintaining the desired single-shrub appearance.