Growing Bigleaf Hydrangeas (Hydrangea macrophylla)
The large blue and pink flowers of the bigleaf hydrangea have made it one of the more popular shrubs for decades. This is one reason the National Garden Bureau declared 2020 The Year of Hydrangeas.
Hardy in zones 6 to 9, these beauties prefer morning sun and some afternoon shade with moist well-draining soil. Bigleaf hydrangeas flower on the previous season’s growth, so only prune right after flowering and only if needed.
Those gardening in colder regions need to grow varieties that flower on old and new growth. In spring remove any winter damaged stems, fertilize and keep the soil moist to encourage flowering.
Bigleaf hydrangea flower color is influenced by the soil’s pH. In acid soil, aluminum is more available resulting in blue flowers. It is less available in alkaline soils where the flowers will be pink.
A bit more information: Many northern gardeners have complained about the lack of flowers on some repeat blooming bigleaf hydrangeas. An application of Milorganite fertilizer in the spring along with proper watering have helped many gardeners nudge their plants into flowering. The non-leaching phosphorus and low nitrogen promote balanced growth. In addition, research found that when the microorganisms work on releasing the nutrients from the Milorganite pellets it also makes some of the phosphorus that promotes flowering and potassium available to the plants.
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