The Pom Pom Hydrangea is a highly sought-after ornamental shrub, instantly recognizable by its large, dense, globe-shaped flower heads. These lush, ball-like blooms are characteristic of the Hydrangea macrophylla ‘Mophead’ group, though the term may also describe certain Hydrangea arborescens cultivars. This botanical distinction is important because it dictates the plant’s care regimen, particularly its pruning schedule. Gardeners are drawn to these shrubs for their dramatic, long-lasting summer color, which can range from deep blue to vibrant pink or pure white, making them a stunning focal point in any landscape.
Selecting the Site and Planting
The correct location is the foundation for a healthy, bloom-filled Pom Pom Hydrangea, requiring a balance of light and protection. The ideal spot provides morning sun exposure followed by protective afternoon shade, especially in the hottest regions. Direct sun during the intense afternoon hours can scorch the large leaves and cause the plant to wilt, stressing it and reducing flower production. Hydrangeas need a few hours of direct light to develop strong stems and abundant flower buds.
The soil composition must be rich in organic matter and reliably well-drained. Before planting, incorporate compost or aged manure into the soil to improve structure and fertility. Dig a planting hole that is two to three times wider than the root ball but no deeper, ensuring the top of the root ball is level with the surrounding grade. Backfill the hole with the amended soil, gently tamping it down, and immediately follow up with a thorough deep watering.
Soil pH plays a direct chemical role in the flower color of Hydrangea macrophylla varieties. Highly acidic soil (pH 6.0 or lower) makes aluminum available to the plant, resulting in blue or purple flowers. Conversely, alkaline soil (pH 7.0 or higher) binds the aluminum and produces pink or red blooms. Gardeners can use aluminum sulfate to acidify the soil for blue tones or garden lime to increase alkalinity for pink tones.
Essential Routine Care
Consistent and deep watering is the most significant maintenance task for Pom Pom Hydrangeas throughout the active growing season. Their large leaves transpire moisture quickly, so they require the soil to be consistently moist, though never soggy. Aim to provide a deep soaking one to two times per week, adjusting the frequency based on local rainfall and temperature. Watering should be done at the base of the plant in the morning, which allows the foliage to dry completely and reduces the risk of fungal issues.
A balanced, slow-release granular fertilizer should be applied in early spring as new growth begins to emerge. A formulation such as a 10-10-10 provides the necessary nitrogen (N), phosphorus (P), and potassium (K) for overall plant health. Avoid high-nitrogen fertilizers, as an excess promotes lush, leafy growth at the expense of flower production. For reblooming varieties, a second, lighter application in mid-summer can provide a boost for the subsequent flush of blooms.
Monitoring for common pests and diseases helps maintain the shrub’s health. Powdery mildew appears as a white, dusty coating on the leaves, often due to poor air circulation. Black spot is another common fungal issue, appearing as dark, irregular spots. Pruning out the oldest interior stems can improve air flow, and ensuring the plant is watered at the soil level helps prevent these issues.
Pruning for Shape and Bloom
Pruning techniques for Pom Pom Hydrangeas depend entirely on whether the specific cultivar blooms on old wood, new wood, or both. Traditional Hydrangea macrophylla mopheads bloom on old wood, meaning they set next year’s flower buds on the stems that grew this season. Pruning this type in the fall or spring will inadvertently remove the latent flower buds and eliminate the summer bloom.
Structural Pruning for Old-Wood Bloomers
For old-wood bloomers, any necessary structural pruning to reduce size or shape should be completed immediately after the first flush of flowers has faded in mid-summer. Structural pruning involves cutting back up to one-third of the total stems. Focus on removing the oldest, woodiest canes right down to the ground. This regenerative process encourages the plant to produce strong new growth that will mature and set buds for the following season.
Deadheading
Deadheading, the removal of spent flowers, is a lighter task performed throughout the blooming period to improve the plant’s appearance. Use clean, sharp pruners to snip the faded flower head just above the first set of healthy leaves or buds below the bloom. Stop all pruning and deadheading by late summer to ensure the newly formed buds have adequate time to harden before winter. If the Pom Pom Hydrangea is a rebloomer, producing flowers on both old and new wood, it offers more flexibility and will still bloom even if the old-wood buds are damaged.
Preparing for Dormancy
As the growing season concludes in late fall, preparing the Pom Pom Hydrangea for dormancy focuses on protection and hydration. The most important late-season task is to give the shrub a deep, thorough watering just before the ground freezes solid. Well-hydrated roots are better equipped to withstand the drying winter winds and freezing temperatures.
Applying a thick, insulating layer of organic mulch around the base of the plant helps protect the crown and roots from cold damage and the destabilizing effects of freeze-thaw cycles. Spread a layer of shredded bark, straw, or compost, but keep the mulch from directly touching the plant’s main stems. Leaving the faded flower heads on the plant throughout the winter provides natural protection for the delicate dormant buds below.
In colder USDA Hardiness Zones, particularly those below Zone 8, additional physical protection may be needed for old-wood bloomers to ensure bud survival. Loosely wrapping the entire shrub in burlap or erecting a cylindrical cage filled with insulating material helps shield the stems from extreme cold. This practice reduces the risk of winter die-back, which could result in a lack of flowers the following summer.