Hydrangea How-to's: Home

Hydrangeas are a popular shrub for the homeowner. From mid-summer until fall, they produce a glorious show in gardens. Versatile shrubs, they thrive in both sandy coastal soils and in shady woodland sites.

When we think of hydrangeas we usually think of bigleaf hydrangeas (Hydrangea macrophylla) and mountain hydrangeas (Hydrangea serrata). These are deciduous shrubs that are native to seacoasts and mountain valleys in Japan and divided into two types by the shape of their flowers. Mop-head types (sometimes called hortensias) have large, ball-shaped, flower clusters. These are sterile flowers with the fertile flowers often hidden underneath. Lace-cap types have flat, delicate clusters, with the sterile flowers on the outer edges and the fertile flowers displayed in the center. Most species of hydrangeas can have either mophead or lace-cap types of flowers, depending upon the relative numbers of fertile to infertile flowers for a specific cultivar. Hydrangea serrata have only lace-cap flowers.

These shrubs are hardy from zones 5 to 9 and range from 3 to 6 feet tall. Despite all the complicated instructions regarding pruning hydrangeas correctly, most need no pruning to grow well. Choose a space that accommodates the full size of your chosen cultivar and you will save yourself many hours of pruning. Just remove dead branches at any time.

An ideal planting location gives your hydrangea morning sun and dappled sunlight in the afternoon, so the east side of a home is often a good choice. They present few challenges in well-drained soil that is amended with organic matter. The biggest problem that gardeners face is lack of flowers.

Why don't my hydrangeas bloom?

Shade

One common cause for lack of flowers is too much shade. Hydrangeas do well in partial shade provided by tall deciduous trees. Plant your hydrangeas in an area where they receive morning sun. They also thrive in full sun but may need extra water on hot summer days. (Bigleaf hydrangeas survive full sun in coastal areas once they are established.)

Care

Cultural practices are sometimes the cause of the lack of flowers. If hydrangeas are given too much, high-nitrogen fertilizer, they may produce lush foliage with few flowers. Fertilizer applied to lawns may find its way into your hydrangea bed and cause the same problem.

Good watering practices are also important for healthy plants. Hydrangeas benefit from 1 inch of water a week during summer. Bigleaf hydrangeas in full sun may need up to 2 inches a week during the hottest summer days.

Cold winters

Winter dieback can be a problem in colder regions. Check that the hydrangea you have selected is winter hardy in your USDA growing zone. If you plan to keep your hydrangea in a container, it needs to be hardy in one or two zones colder than the one you live in because the roots will be more exposed.

Plant your hydrangeas in a sheltered spot or try creating a burlap windscreen or a burlap frame filled with dry leaves as winter approaches. Winter temperatures tend to be more constant on a north- or east-facing site. The south and west side of your property will heat up in the winter sun and may cause hydrangea buds to open prematurely. A spring freeze that is almost unnoticeable can also ruin developing buds.

Pruning at the wrong time

The biggest culprit for a lack of flowers is incorrect pruning. Bigleaf hydrangeas flower on old wood. They need minimal pruning, but if you would like to reduce the size of the plant, technically the best time to prune these shrubs is immediately after flowering. However, if cold winters are known to kill the tips of the branches in your growing area, prune in spring instead. Before the hydrangea starts to leaf out, remove deadwood and cut the stems back to a healthy set of buds. If you have an established shrub, you can also take out several of the older stems at this time. This will alleviate congestion and encourage new growth. Make sure that you do not remove too many buds, otherwise you will loose your blooms. The buds have already formed when you prune mop-head and lace-cap hydrangeas in the spring and every portion of stem you remove reduces flowering.

For information on pruning other types of hydrangeas, see the Types of Hydrangeas tab at the top of this page.

The relationship of soil pH to hydrangea flower color

The color of bigleaf hydrangea blooms is not only determined by the particular cultivar, but also by the amount of aluminum in the soil and the soil pH. The soil pH will determine how available aluminum is to the plant. Acidic soil will  give you blue flowers (aluminum available to the plants) and alkaline soil will give you pink flowers (aluminum unavailable to the plants).

To decrease the acidity of your soil (to change flowers from blue to pink), add hydrated lime to your soil in the spring. To increase the acidity of the soil (to change flowers from pink to blue), add aluminum sulfate to your soil in the spring (follow directions carefully on label and don't over-do it.) Otherwise, pay attention to the three numbers on your fertilizer. The middle number is phosphorous. High phosphorous will help lock the aluminum in the soil providing you with a pink hydrangea, while fertilizers that are low in phosphorus and high in potassium will help turn them blue.

Warning:

It is not always easy to manipulate the color of your hydrangea and some of them will not change their color regardless of what you do. On the other hand some of them will change their color if you adjust the soil pH and even provide you with both pink and blue flowers during the same season.

Aside from the ever-popular, bigleaf and mountain hydrangeas, there is a wonderful selection of other species for the home gardener to choose from. Click on the Types of Hydrangeas tab at the top of this page to explore some other common hydrangea species and favorite cultivars.