A hydrangea hedge provides a beautiful, continuous screen of foliage and flowers, offering both privacy and color in the landscape. Unlike a row of individual shrubs, a successful hedge requires the plants to grow together seamlessly to form a dense, uniform wall. Establishing the correct distance ensures the plants quickly interlock their branches without suffering from overcrowding or poor air circulation later on.
Calculating the Ideal Spacing for Density
The fundamental rule for planting any dense hedge is to space the plants closer than their ultimate mature width. This proximity encourages the branches to intertwine, quickly eliminating gaps and forming a solid barrier. For a tight, formal hedge, aim to place the center of each plant at approximately two-thirds of its mature spread.
If a hydrangea variety is expected to reach a mature width of six feet, planting the center of each shrub four feet apart will encourage rapid interlocking. For instance, a smooth hydrangea like ‘Incrediball’, which matures to about five feet wide, should be spaced three to four feet apart for a quick, continuous screen. Spacing them too closely can lead to rubbing, difficult pruning, and increased disease risk due to poor airflow.
If your goal is a looser, more natural screen rather than a dense wall, spacing the plants at their full mature width is appropriate. For example, a large panicle hydrangea like ‘Limelight’, which can grow up to eight feet wide, could be spaced seven to eight feet apart for a more undulating, individual shape. Always consult the specific mature size of your chosen variety, as this measurement dictates the necessary initial planting distance.
Selecting the Right Hydrangea Variety for Hedges
The choice of hydrangea species directly influences spacing due to variations in mature size and growth habit. Hydrangea paniculata (panicle hydrangeas) are excellent choices for taller hedges because they are fast-growing and tolerate more sun. Large varieties, such as ‘Limelight’, require wider spacing, while dwarf types, like ‘Little Lime’, need closer placement.
Smooth hydrangeas (Hydrangea arborescens), including ‘Annabelle’ and ‘Incrediball’, are suitable for mid-sized screens, generally maturing between four and five feet wide. Their natural, mounding habit requires spacing them at the lower end of their mature width range to encourage a solid, unbroken line.
Bigleaf hydrangeas (Hydrangea macrophylla) are better suited for shorter, more informal hedges due to their tendency to be less cold-hardy and their need for more shade. Their mature width varies greatly, but they often require similar spacing to smooth hydrangeas to prevent overcrowding. Selecting a variety that matches the desired final hedge height and width is crucial before calculating the exact planting distance.
Preparing the Soil and Trench for Planting
Before planting, ensure the site receives the correct amount of light for your chosen variety; panicle hydrangeas can handle full sun while bigleaf types prefer partial shade. Hydrangas require well-drained soil and will not thrive in locations where water tends to collect after a rain.
For a hedge, digging a continuous trench is more efficient than individual holes, and this trench should be at least twice as wide as the root balls. Amending the excavated soil with organic materials like compost or aged manure improves drainage and adds necessary nutrients. This creates a large area of loosened soil, allowing young roots to penetrate easily and establish themselves quickly.
While all hydrangeas benefit from rich soil, H. macrophylla and H. serrata are unique because their bloom color is influenced by soil pH. Acidic soil (low pH) results in blue flowers, while alkaline soil (high pH) favors pink blooms. Adjusting the soil pH is not necessary if planting a white-blooming variety, such as a smooth or panicle hydrangea.
Pruning Techniques for Hedge Formation
After planting, a light heading cut on the tips of the main branches promotes bushier growth and forces the plant to produce more side shoots. This early shaping encourages the lateral growth needed for shrubs to merge into a single hedge unit. This ensures the hedge fills in quickly from the ground up, rather than growing tall and leggy.
The timing of subsequent pruning depends on whether the plant blooms on new wood or old wood. Panicle and smooth hydrangeas, which bloom on new wood, should be pruned in late winter or early spring before new growth begins. This allows for aggressive shaping and cutting back to a permanent framework to promote strong stems and large flowers.
Bigleaf hydrangeas, which typically bloom on old wood, require a different approach to avoid removing the next season’s flower buds. Pruning should be done immediately after they finish flowering in the summer, or limited to removing dead or weak wood in the early spring. Regardless of the type, periodically removing the oldest, thickest stems at the base (renewal pruning) rejuvenates the plant and maintains vigor.