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Hydrangeas: Giant Bursts of Garden Color

Question: I’d like to grow hydrangeas. What can you tell me about their growing requirements?

K.G., Anaheim

Answer: Hydrangeas have been grown in California since the beginning of the 1900s and continue to be a popular flowering shrub with their giant flower clusters that come in a variety of colors, including blue, purple, pink and white. They bloom from early spring through summer.

Within the genus hydrangea there are hundreds of cultivars and more than 20 species. H. macrophylla, otherwise known as garden or big leaf hydrangea, performs best in Southern California. Growing from 4 to 8 feet tall and up to 4 feet wide, H. macrophylla is a deciduous shrub with a symmetrical, rounded shape. The plant’s coarse, thick leaves measure up to 8 inches long.

Here are some planting and growing tips:

* Hydrangeas prefer a site with filtered to partial sun. They generally thrive if planted facing east. Full sun is tolerated in coastal areas. In hotter inland areas, they do best with morning sun and afternoon shade. Make sure the planting location also has good drainage.

* For ground planting, dig a hole three times the size of the container. Mix up to 50% with native soil and acidic amendment, like camellia and azalea mix.

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Plant in the hole with the top of the root ball slightly above ground level. Eight to 12 inches from the base of the plant create a 2-inch-high rim of soil to prevent water runoff.

Water soil until it settles, and add more soil if necessary. Finish by applying a 1-to-2-inch layer of mulch.

For container planting, use azalea and camellia mix as your potting soil.

* Regular watering is essential. Never let the soil dry out. Keep the soil moist but not soggy.

* While hydrangeas come in various colors, what you feed them will determine how they will flower in the future. To keep the color of pink and blue blooms, treatments to the soil need to be started in late fall and early winter ahead of the blooming period.

Alkaline or neutral soils make pink flowers, while acid soils yield blue flowers. Southern California tends to have alkaline soil, so if you don’t treat the soil, you will end up with pink flowers. Keep in mind, however, that whites will remain white, some pinks will stay pink and other pinks will only change to purple instead of blue.

To create blue flowers, you need to alter the soil so that it is acidic--a pH of 4.5 to 5.0. To do so, use a balanced, water soluble, acidic fertilizer with little or no phosphates, since phosphates are alkaline. That means a fertilizer that reads 15-2-10, for example.

Each fall or winter, also apply 1 tablespoon of aluminum sulfate per foot of plant height. Mix with water and drench the soil.

To maintain pink flowers, you will need a soil with a pH of 7.0 to 7.5. Use a balanced, water soluble fertilizer and add superphosphates to the soil in the fall or winter.

Soil pH test kits can help determine your soil’s pH level.

* Hydrangeas need little, if any, pruning. Prune only if necessary for size control in the fall after the blooming period. Cut back on stems that bloomed, leaving green stems intact, since new flower buds are forming for next year’s growth during late summer and early fall.

* Fresh-cut or dried hydrangea blooms are excellent in floral arrangements. Dry cut blooms when their color is at its peak by hanging them upside down in a cool, dark place until dry. They will be dry in a few weeks.

For information on the American Hydrangea Society, which is based in Atlanta, call (404) 636-7886.

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Researched by University of California master gardener in training Melissa Grisham of Aliso Viejo.

Have a problem in your yard? University of California Cooperative Extension (UCCE) Master Gardeners are here to help. These trained and certified horticultural volunteers are dedicated to extending research-based, scientifically accurate information to the public about home horticulture and pest management. They are involved with a variety of outreach programs, including the UCCE Master Garden hotline, which provides answers to specific questions. You can reach the hotline at (714) 708-1646 or send e-mail to ucmastergardeners@yahoo.com. Calls and e-mail are picked up daily and are generally returned within two to three days.


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