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Hydrangeas - Popular Plants for the South
by Keith C. Hansen, Extension Horticulturist

During late May through early summer, the vivid blues, pinks and whites of hydrangeas color up yards all across the south. Some common hydrangea questions I get include, "How to make hydrangeas blue or pink?", and, "When to prune hydrangeas?"

There are several different types of hydrangeas. Probably the most familiar hydrangea is what is commonly called the "French" hydrangea (Hydrangea macrophylla), also called mopheads. This showy shrub is not from France, but was extensively hybridized by the French about 100 years ago. An oriental native, there are now two groups of French hydrangeas, the hortensias and the lacecaps. The hortensia group is the one seen most frequently around homes, bearing large clusters or balls of pink or blue flowers. The lacecaps have a center of non-showy fertile flowers surrounded by a ring of showy fertile flowers, giving a more delicate, lacy appearance.

Another common name for this plant is big-leaved hydrangea. The Latin 'Hydra' means water, and that gives you a clue that these large-leaved plants need a lot of water during the summer to keep leaves and flowers from wilting. Hydrangeas do best with a lightly shaded northern or eastern exposure, in rich, well-drained, loamy soil with a thick mulch 4 inches deep to maintain soil moisture.

French hydrangeas are like living litmus paper because the color of the blooms will tell you whether your soil is acid or alkaline. Acid soils produce blue blooms, while alkaline soils turn the flowers pink. Most east Texas soils are acid, and if you'd like pink blooms, apply lime in the fall to change the color next summer. Aluminum sulfate, sulphur or ferrous sulfate will acidify the soil and help promote bluer flowers.

Sometimes a single plant may have shades of both pink and blue at the same time due to varying pH in the soil around the plant. 'Nikko Blue' and 'Merritt's Blue' are two popular cultivars with stable blue flowers.

French hydrangeas look best when periodically pruned. Be sure to prune right after they finish blooming because flower buds are formed in late summer and fall. Remove stems that have bloomed and leave stems that have not bloomed. The stems may look dead in winter, but they contain the leaf and flower buds for next spring. A severe winter may eliminate next year's blooms.

Oakleaf hydrangea (Hydrangea quercifolia) is an outstanding shrub for east Texas. A native to the southeastern United States, this deciduous, medium-sized shrub (6 to 8 feet tall) has several characteristics that make it a winner. First, it prefers a shady or partly shaded site. Morning or late evening sun is ideal. It'll grow in sunnier spots with well-mulched, evenly moist soil.

In late May and June, Oakleaf hydrangea bears attractive, showy, conical inflorescences of creamy white flowers, which later turn pinkish, and persist as a brown papery cone.

Continuing the show in fall, the large (up to 8 inches), oak-shaped leaves (which are attractive all summer) turn a reddish purple or burgandy before dropping in the winter to expose attractive exfoliating bark up and down the upright branches. Leaf color will be more pronounced for plants in sunnier locations.

Use oakleaf hydrangeas wherever a bold texture is needed, such as an accent plant, in a naturalized shrub border, in front of tall evergreens, or near water.

Oakleaf hydrangea has very few pests, is hardy, tolerates a wide range of soil and moisture conditions, is long-lived and readily available. Remember, give it room to grow.

Another white flowered hydrangea is peegee hydrangea (Hydrangea paniculata). This fast-growing shrub can get 15 feet tall if left unpruned. The large flower clusters bloom in late summer.