Hydrangea – Pruning and Colors

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The general rule for pruning is to prune spring blooming shrubs after they flower and summer blooming shrubs in late winter. Think about azaleas. They bloom in the spring and then immediately set buds for next year’s bloom. You have a very short time frame to trim azaleas to ensure blooming the following year. Summer blooming plants bloom on wood that grows in the summer. By pruning in the winter, you are not removing any flower buds.

Hydrangea species vary in which type of wood they bloom on, making pruning a little more challenging. First thing to know is which type of Hydrangea you have and then the rest is easy!

Hydrangea macrophylla- French or Bigleaf Hydrangeas

Pruning: Mophead and Lacecap Hydrangea bloom on old wood. Prune immediately after flowering.

Flower Color: Bigleaf Hydrangeas color is directly affected by pH. The pH will determine the color of the flower in most cases. Hydrangeas like ‘Pink Elf’ and ‘Glowing Embers’ can never turn blue. They may turn a purplish color. Acid soils will cause Bigleaf Hydrangeas to bloom blue and alkaline soils will cause the plant to bloom pink.

Can you change the color by adding an amendment? When you first plant, the blooms may be a variety of colors as the plant acclimates from being grown in a container to in your garden. It is possible to change the color of Bigleaf Hydrangeas, but will time and requires very careful monitoring. Growing the plant in a container may make it easier to control flower color. It is easier to get a flower from pink to blue, than blue to pink. Aluminum must be present for a blue color, but it must be absent to get a pink flower. The pH is important for hydrangeas to be a specific color. Take a soil sample before starting the process of changing the pH. Soil pH of 5 to 5.5 will cause flowers to turn blue, above 6.5 they will be pink and between 5.5-6.5 it will be a melding of the two colors, more like a pinkish purple. Apply aluminum sulfate or sulfur to reduce the pH to this range when you see new growth emerging in April.
To raise apply lime. For complete information changing the soil pH, visit:
http://www.clemson.edu/extension/hgic/plants/other/soils/hgic1650.html

Personally, I’m happy with the color that our soils produce. Remember when you change the pH, you will affect all the other plants adjacent to your hydrangeas.

Hydrangea quericifolia
Pruning: Oakleaf Hydrangea is a native plant. Oakleaf hydrangea also blooms on old wood, so it should be pruned shortly after blooming.

Flower: 4 -12 in. erect panicles of creamy white flowers in summer; fades to pink, then tan; fragrant; good for drying

Size and Culture: 4-8 feet tall. Keep mulch to keep roots cool. Sun to partial shade; prefers moist, well-drained soil but tolerates damp soil.

Hydrangea paniculata
Panicle or Peegee Hydrangea

Pruning: Bloom on new wood, or wood grown in spring and early summer. Better blooming if cut back in late winter.

Flower: 6-8 in. pyramidal panicles of creamy white flowers in summer on new growth; fades to pinkish rose; fertile and sterile flowers

Size and Culture: 8 to 20 feet tall. Drought tolerant; tough, dependable plant; brittle stems; easily wind damaged; can be severely pruned; rapid growth rate; this plant may be damaged by deer
Can be grown as a tree.

Hydrangea arborescens ‘Annabelle’,
Smooth Hydrangea

Pruning: Flower buds produced on new wood. Better bloom if cut back in winter.

Flower; The native Smooth Hydrangea is white, 6 to 8 inches, flattened corymb in summer; opens white then turns green and brown. The named cultivars have typical ball-shaped hydrangea flowers 8 to 12 inches across. Newer cultivars can be found with pink flowers.

Size and Culture: 3 to 6 feet tall. Yellowish brown fall foliage; attracts bees; leaves suffer in full sun and with drought; severely prune in early spring to rejuvenate; blooms on new wood; native to portions of eastern US; this plant may be damaged by deer.