June is the month with blessings from several varieties of the Hydrangea shrub in the Kentucky garden and landscape! Hydrangeas are the number 2 most popular shrub planted in the home landscape. It grows in zones 3-9 and offers different shapes and colors of blooms for the landscape throughout the growing season. This plant is relatively pest free if planted in the correct place for bloom production.
Uses of Hydrangeas
Hydrangeas can be used in mass planting, border, and as an accent or specimen plant.
Types of Hydrangeas:
Smooth Hydrangea- Hydrangea arborescens
Oakleaf Hydrangea- Hydrangea quercifolia
Panicle Hydrangea- Hydrangea paniculata
Bigleaf Hydrangea- Hydrangea macrophylla
Hydrangea means “water lover” in Greek where “hydra” means water and “angeon” means “vessel”. After planting, water hydrangeas consistently throughout their first year. Even after establishment, hydrangeas will require 1 inch of water per week either by rainfall or irrigation. Additional water may be needed in a sunny or windy location. Make sure to give hydrangeas the proper location based on the type being grown and provide ample amounts of mulch to conserve soil moisture and keep roots cool.
How to Adjust Bigleaf Hydrangea Flower Color
For Bigleaf hydrangea also known as Hydrangea macrophylla, blooms can vary by color from true blue, deep purple, to pink according to the soil’s pH or the availability of aluminum in the soil. For example, in acid soils, aluminum is more available and leads to a blue bloom color. In basic or more alkaline soils, aluminum is found in less amounts and gives a pink bloom color.
Altering soil pH for hydrangea production can take up to 6 months and requires a basic soil test for complete accuracy. Based on soil test recommendations, add powdered or pelletized lime or sulfur in the fall for desired pink or blue blooms for the following summer.
Remontant hydrangeas also referred to as “repeat bloomers” are plants that flower more than once in a single growing season. Some top mophead remontant selections include ‘Blushing Bride’, Endless Summer ‘Bailmer’, ‘Decatur Blue’, and ‘Nantucket Blue’. “Twist-n-Shout’ is the only remontant lacecap type. The bigleaf hydrangea cultivars are more strongly remontant. Make sure to fertilize remontant hydrangeas to help support repeat blooming.
In order to prune hydrangea, know the type you have and understand if it blooms on old or new wood.
“Old Wood” refers to previous year’s growth. Hydrangea cultivars with old wood formed the buds the year before.
“New Wood” refers to the current year’s growth. Hydrangea cultivars that bloom on new wood set their buds during the year in which they bloom.
When is the correct time to prune specific hydrangeas?
Smooth hydrangea blooms on the current year’s growth. For this type, prune back by early March, so plants have time to grow stems and form flower buds.
Oakleaf hydrangea– allow this type to grow in its natural form and prune as little as possible. Oakleaf hydrangea flowers are produced on old wood. If pruning is necessary, finish by the end of July to ensure that there is still time for next year’s flower buds to develop.
For panicle hydrangea, pruning isn’t needed. If you would like to create a neater and tidy appearance and help increase the size and number of blooms, cut the plants back hard to approximately two buds. The blooms will develop on new stems, so make sure that this pruning is performed once plants go dormant through early March. If you desire, panicle type hydrangeas can be trained to a tree form unlike other hydrangeas. Begin training at an early age and requires a stake to help support. To keep the tree form shape, remove branches that develop from the trunk several times throughout the year.
Once bigleaf hydrangea is mature, prune no more than one-third of the older branches to the base of the plant in early spring. Pruning will rejuvenate the plant without a large loss of flowers. To reduce size or for shaping, prune after blooms fade but no later than the end of July.
For more information about growing or caring for hydrangeas, please contact the Warren Co. Extension Office at (270) 842-1681.