Hydrangeas Provide Color In Shade

Daniel Gill, Merrill, Thomas A.  |  4/30/2005 1:33:14 AM

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Get It Growing News For 5/20/05

By Dan Gill
LSU AgCenter Horticulturist

Hydrangeas can bring color to your shady beds.

Among the most popular summer flowering shrubs for shady gardens, hydrangeas provide flower clusters like fluffy balls of cotton candy.

From now through July, huge flower heads of pink, blue and blends of those two colors appear above the rich green leaves of these plants.

Potted hydrangeas are popular gifts for Mother’s Day, and they can be a gift that lasts. Once their flowers fade, these gift plants can be planted outside where they will provide beautiful flowers for years to come.

Hydrangeas (Hydrangea macrophylla) are deciduous shrubs originally native to Japan. They need an evenly moist soil and are intolerant of dry conditions. If you allow hydrangeas to wilt excessively, either those growing in pots or in the ground, it will shorten the life of the flowers and can cause the foliage to develop scorched edges.

Display your potted hydrangeas in a bright, sunny window, and make sure the soil stays moist so the plant does not wilt. When the flowers begin to look unattractive (nothing lasts forever), cut off the flower heads and plant the shrub in an appropriate location in your landscape. Blooming hydrangeas also may be available at local nurseries and could be purchased and planted into garden beds now.

Locate hydrangeas in a spot where they receive some shade during the day. A shady (two hours of direct sun) or partly shaded (about four hours of direct sun) bed is ideal. Avoid hot, sunny, dry areas or beds that are baked by the afternoon sun. Morning sun is much preferred by these plants, so an eastern exposure is excellent.

Hydrangeas do best in beds that have been amended with generous amounts of organic matter, such as compost, rotted manure or peat moss. Dig in a 2-4 inch layer of organic matter during bed preparation. The organic matter helps retain moisture in the soil.

Once planted, it is important to keep hydrangeas well watered. Water deeply and thoroughly two or three times a week while they get established and then once or twice a week later on if the weather is dry. Hydrangeas also benefit from a 2-3 inch layer of mulch, such as leaves, pine straw, cypress mulch or pine bark, over their root system to help maintain a moist soil condition.

Interestingly, the colorful parts of the flower head are not part of the flowers at all. What you might think of as petals actually are modified sepals. The actual flowers are tiny, inconspicuous and located in the middle of the four showy sepals. The flowers which have showy sepals are called sterile flowers.

The mophead or hortensia hydrangeas have huge round heads of sterile flowers. Another group, the lacecap hydrangeas, has a center cluster of small fertile flowers, which are not showy, surrounded by a ring of attractive sterile flowers. The popular variegated hydrangea is a lacecap type.

When the colorful flower heads turn green it signals the ideal time to prune your plants. First, cut off the faded flower heads with stems about 4-6 inches. If you are trying to reduce the size of your bush, cut the heads with longer stems.

If there are any especially tall shoots, or if you need to cut the whole bush back to reduce its size, you may continue to cut back shoots to achieve the desired results. Pruning back stimulates new growth – creating a fuller, shapelier bush. This type of pruning must be done by the end of July at the latest. Hydrangeas set their flower buds for the next year in late summer, so any pruning after that removes the flower buds and reduces or eliminates flowers the next year.

The flower heads of hydrangeas are rather unique. Depending on how acid or alkaline the soil the plant is growing in, the colorful sepals can be different colors.

For example, if you have pink hydrangeas and you want them to be blue, treat the soil around the bushes with aluminum sulphate in March and again in October each year. Gradually, over time, the flower heads will turn blue. If your hydrangeas are blue and you want them to be pink, treat the soil around the bushes with lime following the same schedule. It may take a couple of years to be fully effective.

The intensity of the color is controlled by genetics and depends on the variety you are growing. Since white hydrangeas do not have pigment in their sepals, they are white regardless of the soil pH. But the others can be varied.

While thinking of hydrangeas, don’t forget our native oak leaf hydrangea (Hydrangea quercifolia). With its large pointed cones of white flowers, which age to dusty rose, and its dark green attractive leaves, it also deserves consideration for shady areas of your landscape. Larger growing than standard hydrangeas (up to six feet), oak leaf hydrangeas also are deciduous and have the added attraction of orange to burgundy fall color.

Get It Growing is a weekly feature on home lawn and garden topics prepared by experts in the LSU AgCenter. For more information on such topics, contact your parish LSU AgCenter Extension office or visit our Web site at www.lsuagcenter.com. A wide range of publications and a variety of other resources are available.

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Contact: Dan Gill at (225) 578-2222 or dgill@agcenter.lsu.edu
Editor: Tom Merrill at (225) 578-2263 or tmerrill@agcenter.lsu.edu

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