HEAVENLY HYDRANGEAS

PROGRAM: Heavenly Hydrangeas

Hydrangeas are a popular genus of flowering plants, with 70 to 75 species native to Asia and the Americas. They come in both deciduous and evergreen varieties, although the temperate species commonly cultivated in gardens are all deciduous.

During a presentation by Scott Aker, Head of Horticulture and Education at the U.S. National Arboretum, members had the opportunity to learn more about these beloved plants. Scott addressed several common questions about hydrangeas, including their care and characteristics.

One of the most fascinating aspects of hydrangeas is their ability to change color. Scott explained that the color of the flowers, particularly with species like Hydrangea macrophylla (bigleaf hydrangea), can be altered based on the pH of the soil. In acidic soils, hydrangeas tend to produce blue flowers, while in alkaline soils, the flowers turn pink. The addition of aluminum sulfate can help acidify the soil to encourage blue blooms, while lime can be used to make the soil more alkaline for pink flowers.

Another common question is when and how to prune hydrangeas. Scott clarified that the timing of pruning depends on the variety of hydrangea. For those that bloom on old wood (like the bigleaf hydrangea), it's best to prune right after flowering, usually in late summer. This ensures you don't remove next year’s flower buds. However, for varieties that bloom on new wood (like Hydrangea paniculata), pruning can be done in early spring before new growth starts.

As for sun or shade, Scott emphasized that hydrangeas generally prefer a location with morning sun and afternoon shade, particularly in hotter climates. While they can tolerate full sun in cooler climates, too much sun can scorch their leaves and flowers. In more temperate areas, they thrive in partial shade where they receive dappled sunlight throughout the day.

Scott's insights into hydrangea care were incredibly informative, and attendees left with a greater understanding of how to cultivate these stunning plants in their own gardens.