How to Care for Hydrangeas

Phyllis Heuerman
Frederick County Master Gardener Program

Hydrangeas are old-fashioned shrubs that have become extremely popular in recent years. There are more than 100 species of Hydrangea, and within those many subspecies, and cultivars. There is enormous variation in size, flower type, and cold hardiness, even within a species, which make it very difficult to generalize. I will mention just a few of the most popular, readily available Hydrangeas.

By far the most popular Hydrangea on the market today is the one we hear called 'Lace Cap'. The lace cap refers to a flower that has very small bud-like blooms, generally in the center, in combination with larger showy florets on the outside

The most common 'Lace Cap' Hydrangea is of the genus macrophylla. This shrub can grow three to six feet in height. It is a rounded shrub with many unbranched stems coming from the ground. H. macrophylla is cold hardy to Zone 6, but generally needs protection in our area if you want it to bloom and grow to its full potential. This Hydrangea blooms in late June, July or August, depending upon the cultivar. The relatively flat-topped flowers range in color from white, to pink, to blue.

H. macrophylla blooms on buds formed from the previous year's growth. In order for it to bloom the buds have to make it through the winter. Without protection in Zone 6, the buds will often die in the winter even if the branches survive. In many winters the entire shrub can die to the ground. Although it will come back with lush new growth, there will be no blossoms the following summer. To assure that your H. macrophylla blooms, wrap it in a chicken wire cage filled with leaves for the winter.

One note of interest - most of the florists' Hydrangeas that are that are sold as potted plants are a delicate variety of H. macrophylla. They will not produce flowers if planted outside because their buds are not cold hardy in this area.

If you want to try a more reliably winter hardy Hydrangea and one that has good flowers for drying, I can recommend a couple. The H. quercifolia is native to this part of the United States and is a beautiful, upright shrub. The stems have some but not many branches. The leaves are lobed like an oak leaf and turn beautiful shades of orange and red in the fall. It is an open shrub that grows 4 to 6 feet high, and is hardy to Zone 5. The flowers are white and open in June or July. They last for 3 to 4 weeks, often turning a purplish pink as they age. Flowers can be 10 inches long or more, depending upon the cultivar you select. The H. quercifolia blooms on the previous year 's growth like the H. macrophylla, but it is sufficiently winter hardy that it does not generally need any special protection to assure bloom. Beware; one drawback for some people is that the shrub forms colonies through underground runners if not kept in check.

The old-fashioned Hydrangea that we all remember from our grandmothers' yards is probably the H. paniculata 'Grandiflora'. This is also known as the 'Pee Gee Hydrangea'. This Hydrangea can become a 15 to 25 foot tree. (If you cut it back each year you can keep it as a shrub.) The branches of the tree arch under the weight of the flowers, producing a very graceful shape. It is hardy in Zones 3 to 8. In August it produces large white pyramid-shaped flowers that gradually change to a purplish pink. The flowers average 6 to 8 inches long. The flowers are easily dried. Just pick them and put them in a vase with no water. You will have them all winter. The H. paniculata blooms on new growth each year.

Because of the wide variety of Hydrangeas available, it is important that you know exactly what you are getting. If your plant is not in bloom when you buy it, ask to see a picture of the flower. If no picture is available, go somewhere else. Also make sure you know exactly what species you are getting, how cold hardy it is, and how large it will grow.

Once you have selected your Hydrangea, growing it is relatively easy. Most Hydrangeas are natural woodland plants and like some shade. Morning or late afternoon sun is OK, but the flowers can burn if exposed to mid-day sun. If a Hydrangea has been planted in a poor location is usually easy to move; it has a relatively small compact root ball. Hydrangeas will grow in almost any soil, but will do better if the soil retains moisture. They should be watered frequently enough that the soil does not completely dry out.

The flowers of many but not all H. macrophylla will range in color from pink to blue depending upon soil acidity. Acid soils produce blues and alkaline soils produce pinks. If you want to encourage one color, add lime to soil to make the soil more alkaline or iron sulfate to make it more acid.

Hydrangeas do not demand a lot of special fertilizing. A good balanced fertilizer can be applied in the late winter or early spring. Mulching of your Hydrangeas is a good practice as it helps hold in water around the roots of the plant. The decaying of organic mulch will also add nutrients to the soil.

Finally, a word about pruning. Hydrangeas do not require pruning except to remove dead wood. If you want to prune to encourage a particular shape, time the pruning based upon whether the Hydrangea blooms on the current or previous year's growth. If it blooms on the previous year's growth, prune right after it blooms. If it blooms on the current year's growth, prune in late winter or early spring, while it is dormant.

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