With dozens of species and even more varieties, hydrangeas (Hydrangea spp.) have been popular garden plants for decades. Their flowers now come in a wide array of colors, including bright blue, deep red, and pale green. Some hydrangeas have large, round flower clusters while others have smaller, flatter, and more delicate flowers. The foliage also varies depending on the species. Plus, these versatile shrubs thrive in sandy coastal soils, shady woodland sites, and almost everything in between. To ensure that hydrangea shrubs have time to establish a healthy root system before blooming, it is best to plant them in fall or early spring. Once planted, hydrangeas are rapid growers, averaging 2 feet or more of growth per year.
|Botanical Name||Hydrangea spp.|
|Common Names||Hydrangea, hortensia|
|Mature Size||Up to 15 feet|
|Sun Exposure||Full, partial|
|Bloom Time||Mid-summer through fall|
|Flower Color||White, blue, green, red, pink, purple|
|Hardiness Zones||5—9 (USDA)|
|Native Area||Asia, the Americas|
|Toxicity||Toxic to people, animals|
Most hydrangeas can adapt to a wide range of growing conditions. They are generally hardy from USDA growing zones 5 to 9. And as long as they are planted in well-draining soil with plenty of organic matter, they should grow well.
Plan to water your hydrangeas regularly, especially in hot and dry weather. And fertilize them once a year. You also might need to do some pruning each year, but it shouldn’t be excessive.
Watch Now: How to Grow and Care for Hydrangeas
Too much shade can reduce a hydrangea shrub's flower output. Hydrangeas do well in the partial shade provided by tall deciduous trees, especially if they receive morning sun and the partial shade is in the heat of the afternoon. They will also thrive in full sun but might need extra water on hot summer days.
In general, hydrangeas can tolerate a wide range of soil types. One of the perks of growing hydrangeas is being able to change their flower color. Although somewhat determined by cultivar, the color can be tweaked by the amount of aluminum in the soil and the soil pH. The soil pH determines how available aluminum is to the plants. Acidic soil (aluminum available to the plants) will give you blue flowers, and alkaline soil (aluminum unavailable to the plants) will give you pink flowers.
To decrease the acidity of your soil and change flowers from blue to pink, add hydrated lime to the soil in the spring. To increase the acidity to change flowers from pink to blue, add aluminum sulfate to your soil in the spring, or mulch with oak-leaf mulch.
Hydrangeas prefer a deep watering at least once a week unless you've had rainfall. During particularly hot weather, slightly increase the amount of water you give your plants, but make sure they're not sitting in soggy soil.
Temperature and Humidity
Hydrangeas prefer fairly mild temperatures. In areas with bitterly cold winters, dieback (a plant dying from the tips of its leaves inward) can be a problem. Protect your hydrangeas from cold winds by planting them in a sheltered spot or with a burlap windscreen or burlap frame filled with dry leaves. A north- or east-facing site, where temperatures remain somewhat constant, is a better choice than a spot on the south and west side of your property, which will heat up in the winter sun and can cause buds to open prematurely and be vulnerable to cold snaps. Furthermore, hydrangeas prefer moderate to high humidity, as dry climates can cause the leaves to wilt.
If your soil is rich in nutrients, you likely won't have to fertilize your hydrangeas. In fact, if hydrangeas are given too much high-nitrogen fertilizer, they might grow full and lush but with fewer flowers. If your soil is not rich, apply a flowering shrub fertilizer in the spring.
Are Hydrangeas Toxic?
Hydrangeas contain cyanogenic glycosides, which are toxic both to people and animals when ingested. The leaves, buds, and flowers have higher concentrations of this compound.
Symptoms of Poisoning
Symptoms of toxicity in both people and animals include nausea, vomiting, gastrointestinal upset, diarrhea, and lethargy. If you suspecting poisoning, contact a medical professional as soon as possible.
There are two main groups of hydrangeas: plants that bloom on new growth (the current year's stems) and those that bloom on old growth (last year's stems). Some varieties include:
- Hydrangea macrophylla: Also known as bigleaf hydrangea, this species grows to around 6 to 10 feet tall and wide and has leaves that reach around 6 inches long.
- Hydrangea arborescens: Known as smooth hydrangea, this shrub reaches around 3 to 5 feet tall and wide and produces white to pink flowers.
- Hydrangea quercifolia: Commonly called oakleaf hydrangeas, this plant reaches around 7 feet tall and wide and sports white to purplish-pink flowers.
Hydrangeas typically need minimal pruning. But if you would like to reduce the size of your plant or prevent it from flopping over too much, you can remove some of the older canes after the flowers fade. This will reduce crowding and encourage new growth.
The exception to this rule is when cold winters kill the tips of the branches. Then, you should prune in the spring, removing the dead wood and cutting back the stems 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. Just don't remove all the buds, or you will lose your blooms for that season.