Hydrangeas are ornamental shrubs, prized for their abundant, long-lasting flowers that add significant visual interest to a landscape. Pennsylvania’s climate presents a varied environment for these plants, ranging across USDA hardiness zones 5 through 7. Successful establishment depends on careful timing and species selection to manage the state’s cold winters and warm summers.
Optimal Timing for Planting
The best time for planting hydrangeas in Pennsylvania is during the cooler “shoulder seasons,” which minimizes stress on the newly transplanted shrub. Planting in early Spring, after the last severe frost has passed, is a suitable option. This timing allows the roots to begin establishing themselves before the intense heat and potential drought of mid-summer arrives.
Early Fall is frequently considered the most advantageous time. When planted in September or early October, the soil is still warm enough to stimulate root growth, but the air temperatures are moderate, reducing the plant’s moisture loss. The goal is for the root system to be well-developed at least six weeks before the ground freezes solid for winter dormancy. Avoid planting during peak summer heat or when the ground is frozen, as these conditions are highly stressful.
Selecting the Right Location and Soil Preparation
Hydrangeas generally flourish in a location that provides morning sunlight and afternoon shade, which protects them from the intense summer heat. This balance of light allows for sufficient energy production for blooming without causing the plant to wilt. Ensure the selected site has well-drained soil, as hydrangeas are sensitive to standing water, which can lead to root rot.
Before planting, enriching the soil with organic matter such as compost or aged manure is recommended to improve both fertility and drainage. The soil pH is an important consideration, especially for Hydrangea macrophylla (Bigleaf hydrangea), as it determines flower color. Acidic soil, with a pH of 6.0 or lower, makes aluminum more available to the plant, resulting in blue blooms. Since many Pennsylvania soils are naturally acidic, blue flowers may be the default color, while a pH above 6.5 results in pink flowers.
Essential Care for New Plant Establishment
The first year after planting is crucial for establishing a robust root system and requires consistent moisture management. Newly planted hydrangeas need deep, regular watering to keep the soil consistently moist, but not saturated. Watering deeply encourages the roots to grow downward, making the plant more resilient to future dry spells.
Applying a two to three-inch layer of organic mulch, such as shredded bark, around the base of the plant is recommended. Mulch helps to regulate the fluctuating soil temperatures common in PA and conserves soil moisture by reducing evaporation. If planting occurs late in the fall, a thick layer of mulch or a protective burlap wrap can offer insulation to the root crown, protecting it from the harsh temperatures of an early winter.
Choosing Hydrangea Varieties for Pennsylvania Success
Not all hydrangeas possess the same cold hardiness required to reliably bloom across all of Pennsylvania’s hardiness zones.
Panicle Hydrangea (Hydrangea paniculata)
This is the most reliably cold-tolerant species, thriving even in the colder Zone 5 areas of the state. Panicle varieties, like ‘Limelight’ or ‘Quick Fire’, bloom on new wood. This means their flower buds develop on the current season’s growth, making them immune to damage from severe winter temperatures.
Bigleaf Hydrangea (Hydrangea macrophylla)
This species, which includes the classic mophead and lacecap types, is more challenging because it often blooms on old wood from the previous season. In the colder PA zones, winter temperatures can kill these old flower buds, resulting in a year without blooms. For gardeners determined to grow Bigleaf hydrangeas, selecting newer, reblooming cultivars that set buds on both old and new wood offers a much higher chance of success.
Smooth Hydrangea (Hydrangea arborescens)
The Smooth Hydrangea, such as the ‘Annabelle’ cultivar, is a native species. It also blooms reliably on new wood and is tolerant of the region’s extremes.