The genus Hydrangea provides a multitude of beautiful shrubs that can add dramatic visual appeal to just about any landscape. Below is a list of some basic practices to follow that will help to ensure the health and vigor of these common landscape plants.
1. Plant Selection is Paramount
Choosing a species or cultivar (cultivated variety) of hydrangea that will not only provide the aesthetic qualities that you’d like but will also thrive in the allotted space, soil conditions and the amount of sunlight that the plant will receive is a challenge. The mature size of the shrub is a primary factor when deciding which hydrangea to choose. The height and width of fully grown hydrangeas can vary widely from 2’ to well over 10’, so the initial plant selection is extremely important. Allow for future growth as well as adequate air circulation when siting these shrubs.
2. Let the Sun Shine… or Not
Most species of hydrangea will perform best in partial shade conditions. Ideally, this will mean about 4 hours of morning sun followed by some shade or filtered shade during the afternoon. Most Panicle Hydrangeas will tolerate full sun whereas Climbing and Bigleaf Hydrangeas can be planted in areas with more shade.
3. Soil and Water Needs
In general, hydrangeas prefer loamy soils that are rich in organic matter. Medium moisture levels are important but drainage is especially critical. They will not tolerate poor drainage or wet feet. Hydrangeas have fairly shallow root systems, so watering during establishment and droughts is key as well as maintaining a 3” layer of organic mulch. For most species and/or cultivars a neutral pH of about 6.5 is adequate, although pH levels may have an effect on the flower color of some species.
4. Pink or Blue Color?
Just about all hydrangea flowers will change color tones as they age. However, only the flowers of Bigleaf and Mountain Hydrangeas can be controlled in a predictable way. There is plenty of misinformation out there as to how best to achieve your desired color. Pennies and nails placed in the soil won’t work. In very general terms the flowers of Bigleaf and Mountain Hydrangeas can be altered with a lowered pH and the presence of Aluminum in the soil. Lower pH levels in the 5.0-6.0 range will produce flowers with blue tones while a pH above 6.0 will result in pink flowers. A pH meter or soil test is needed to determine your baseline pH. A common way to lower the pH for blue flowering is to amend the planting soil with Aluminum Sulfate but don’t overdo it! Excessive amounts of Aluminum are toxic to plants and may inhibit proper root development. Keep in mind that the effects of the amendment won’t be apparent until the new buds are formed which in most cases is during the following year’s growth. In general, it’s easier to manipulate flower color from pink to blue than in the reverse.
Interested in learning more about the hydrangeas mentioned? 6 Types of Hydrangeas in the Garden is the first article in this series that describes the most common types of hydrangeas found in western PA.
5. To Prune or Not to Prune?
Hydrangeas form their flower buds either on the current season’s growth in the spring, also known as new wood, or later in the year on stems that were formed during the previous summer, or old wood. New wood bloomers include the Panicle and Smooth hydrangeas and should be pruned during the late winter or early spring. You can remove up to about 1/3 of the shrub’s height to encourage vigorous new growth and stronger stems. Bigleaf, Mountain, Oakleaf and Climbing Hydrangeas bloom on old wood and pruning isn’t necessary except to deadhead or to remove broken, diseased or rubbing stems. There are numerous Bigleaf and Mountain Hydrangeas that are rebloomers or remontant. These cultivars flower on old and new wood and pruning isn’t really required.
6. Why Are There No Flowers?
The absence of flowering on a particular plant almost always is caused by one of 3 factors. The weather can damage the flower buds of species that bloom on old wood as the buds must overwinter and remain viable until spring. It’s usually not extremely cold temperatures but the freeze/thaw cycles that damage these buds. Next, our friends the deer. During times of lean availability for food deer may browse the stems and buds of old wood-blooming hydrangeas. The last factor is outlined in tip number 5. Know your species and when to prune or not to prune. If you prune a shrub that blooms on old wood during the spring you are essentially removing the flower buds for the coming season.
