With dozens of species and even more varieties, hydrangeas (Hydrangea spp.) have been popular ornamental garden plants for decades with blooms that come in a wide array of colors, including white, many shades of blue and pink, maroon, red, and even pale green. Some hydrangeas have large, round flower heads while others have smaller, flatter, and more delicate flowers, along with varying foliage shapes depending on the species. To ensure that hydrangea shrubs have time to establish a healthy root system, plant them in the fall or early spring. Hydrangeas are rapid growers, averaging two feet or more of growth per year. Be aware that the plant is toxic to humans and animals.
Watch Now: How to Grow and Care for Hydrangeas
|Common Names||Hydrangea, hortensia|
|Botanical Name||Hydrangea spp.|
|Plant Type||Deciduous shrub|
|Mature Size||Up to 15 ft. depending upon variety|
|Sun Exposure||Full, partial|
|Soil pH||Any pH but it can influence bloom color|
|Bloom Time||Mid-summer through fall|
|Flower Color||Varies depending on species: white, blue, pink, maroon, red, purple, and pale green|
|Hardiness Zones||5—9 (USDA)|
|Native Area||Asia, the Americas|
|Toxicity||Toxic to humans and animals|
Most hydrangeas can adapt to a wide range of growing conditions. They are generally hardy from USDA hardiness zones 5 to 9. If they are planted in well-draining soil with plenty of organic matter, they should grow well. These versatile shrubs thrive in sandy coastal soils, shady woodland sites, and almost everything in between.
Plan to water your hydrangeas regularly to keep them consistently moist, especially in hot and dry weather and fertilize them once in the spring.
The right time to prune a hydrangea varies according to the hydrangea species and the time of year when they set buds.
Too much shade can reduce flower output. Hydrangeas do well in the partial shade provided by tall deciduous trees, especially if they receive morning sun and the partial shade occurs 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 but they grow best in fertile, humus-rich soil. A notable characteristic of Hydrangea macrophylla is that you can control bloom color by adjusting the soil pH. Acidic soil with a pH of 6.0 or lower produces blue flowers and neutral to alkaline soil with a pH of 7.0 or higher produces pink blooms.
Hydrangeas need consistent moisture throughout the growing season: give your hydrangeas a deep drink of water one to two times every week. If your area has had significant rainfall, you can cut back on supplemental watering. Each time you water, water deeply until the ground feels saturated but is not waterlogged. A light watering every day is not sufficient because the water will not reach the root system to hydrate the plant.
During particularly hot weather, increase the amount of water you give your plants so the soil remains damp, but make sure they're not sitting in soggy soil. To know if you need to water your hydrangea, stick your finger down about four inches into the ground and if it feels dry to your fingertip, it's time to water.
In extremely hot weather, hydrangeas might curl their leaves and appear wilted. This is a built-in protection and does not necessarily mean that the plant needs water. If you observe this behavior, take another look at the plant at dusk to see if it has recovered once temperatures have cooled down.
Temperature and Humidity
Hydrangeas prefer fairly mild temperatures. In areas with bitterly cold winters, dieback can be a problem if the hydrangea is located in an unprotected area or one that receives too much winter sun.
Because hydrangeas prefer to grow in partial shade, they usually do best when planted in a north- or east-facing site, where winter temperatures remain somewhat constant. Avoid planting on the south and west side of your property where the warmth of winter sun could cause buds to swell prematurely and become vulnerable to cold snaps.
Hydrangeas prefer moderate to high humidity and dry climates can cause their leaves to brown and become dry.
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, the foliage will be full and lush but with fewer blooms. If the soil is not fertile, in the spring spread of layer of organically rich compost around the plants or apply a fertilizer suitable for flowering shrubs.
Types of Hydrangea
From the many species of hydrangea, the following are the most commonly used as ornamental shrubs. Some of these hydrangea species bloom on new growth (the current year's new stems) and those that bloom on old growth (last year's stems) .
- Hydrangea macrophylla: Also known as bigleaf, mop head, or lacecap hydrangea, this species grows six to ten feet tall and wide and has six-inch leaves. Bloom color is affected by soil pH; acidic soil produces blue blooms and alkaline soil produces pink blooms. Buds for the following year are set in mid-summer through fall.
- Hydrangea arborescens: Known as smooth hydrangea, this shrub reaches around three to five feet tall and wide and produces white to pink flowers. Buds are set on new stems in spring.
- Hydrangea quercifolia: Commonly called oakleaf hydrangea, this plant reaches around seven feet tall and wide with white to purplish-pink flowers. Its leaves look similar to the oak tree, thus its common name. Buds are set in mid-summer through fall.
- Hydrangea paniculata: Commonly called panicle hydrangea, the blooms on this species are cone-shaped rather than round or flat. For many cultivars, the flowers start out white and gradually change to light pink and then to a darker pink as they mature. This plant grows quite large if left unpruned, up to 15 to 20 feet tall and wide. This species blooms on new stem growth.
Hydrangeas rarely produce seeds, but there are two common ways to propagate the plant. Taking stem cuttings at the right time may result in stronger, more resilient roots that nearly guarantee success when transplanting them into the ground. The second method is to root the hydrangeas right into the ground without having to cut into the shrub until the last step. This is the preferred method if you want to fill gaps between shrubs in your garden or you want a more dense stand of shrubs.
Propagating by cuttings
- In the very early fall, select a new growth stem at least six-to-eight inches long that does not have a flower. New growth will be lighter green than old growth.
- With a sterile, sharp pruner, cut the stem below a leaf node (a node signifies where a set of leaves are set to grow). Keep a set of leaves on the stem in addition to a node.
- Strip the bottom leaves, but keep the top set of leaves. Carefully cut the remaining leaves in half horizontally (crosswise), not vertically.
- Dip the bottom of the cutting in rooting hormone.
- Place the end of the cutting into a small eight-to-ten inch pot filled with damp potting soil. (One pot can hold several cuttings.)
- Make a mini-greenhouse by covering the pot with a plastic bag and closing it at the bottom of the pot. Cut a couple of small slivers on top of the bag so the cutting can breathe. Do not let the bag touch any of the leaves.
- Put the pot in a spot that is away from any direct sunlight and keep the soil slightly damp.
- In two to four weeks, a root system should begin to develop. You can transplant the cutting so that it can have the winter to establish a strong root system.
Propagating by rooting branches directly in the soil
- Bend down a long stem/branch so that a large piece of it touches the soil.
- Trim leaves from the part of the branch that is touching the soil.
- Push the branch down into the soil as best as you can without breaking the branch. You could also push the tip of the branch into the soil.
- Secure the branch by weighing it down with a brick or large rock. You won't injure the branch.
- Water the branch just as you typically water the parent hydrangea.
- Occasionally remove the weight and gently tug on the branch to see if it has rooted. Once rooted, you no longer need to weigh it down.
- Once it has rooted, you will need to clip the branch from its parent plant so the new shrub will be self-sustaining.
- If you do want to dig up the newly rooted shrub to move it, wait a couple of more weeks after you've clipped it so it can be strong enough for transplanting.
Some types of hydrangeas, such as the bigleaf hydrangea, can be susceptible to winter bud damage. If you live in a very cold area with harsh winters, protect your hydrangea plants from cold winds by wrapping them with burlap or putting up burlap screening. You can also tie the branches together along with the burlap to give them extra help to survive winter. Remove the burlap when the buds begin to swell.
Common Pests & Plant Diseases
The usual types of garden pests can affect hydrangeas, including aphids, black vine weevil, the four-lined plant bug, Japanese beetles, and spider mites. Rose chafer pests can injure the plant by eating and leaving skeletonized leaves behind. Chemical insecticides or less harsh insecticidal soaps may help eliminate most of these insects, but avoid using them during the bloom period. Instead, hand pick these pests into pails of soapy water.
Hydrangeas are susceptible to diseases including botrytis blight, powdery mildew, and other viruses such as yellow or brown leaf spotting. Fungicides can help with most problems, but destroy plants infected with viral spotting.
Common Problems With Hydrangea
Here are the most common problems that can occur with hydrangeas.
Hydrangeas may not bloom every season. The reason could be pruning at the wrong time of year, damage to buds during unexpected spring or winter cold snaps, or at some point you may have overfertilized the plant.
The right time to prune a hydrangea varies according to the hydrangea species and the time of year when buds are set. Thus, it is important to know the type of hydrangea you are growing in order to know when to prune it.
Hydrangea leaves can droop due to lack of water. This happens during bloom time or very hot, dry weather, so keep hydrangeas consistently moist.
However, drooping leaves might not always be a sign that a hydrangea needs water. These plants have a built-in protection mechanism where they will curl their leaves downward In extremely hot weather and appear to be wilted. When daytime temperatures are around 90 degrees Fahrenheit or higher and you observe this behavior, take another look at the plant at dusk to see if it has recovered once temperatures have cooled down. If the plant is still wilted as temperatures cool, that could be a sign of dry soil that requires a deep watering.
Yellowing leaves can indicate that a plant has been overwatered, underwatered, or overfertilized. It might be possible to save the shrub by saturating the roots if the problem is that it's too dry or overfertilized. Otherwise, you may need to dry out the roots of an overwatered shrub in the hope that it save the plant.
Brown Leaf Tips or Edges or Tips
This problem can occur if the roots have been burned by over-fertilization. Brown edges or tips can also occur if too much aluminum sulfate was added to the soil to change the color of the blooms. If this occurred, flush the soil with water to remove the excess salts or fertilizers. Then, let the soil surface dry for a day or two before watering again, and abstain from fertilizing until the plant is healthy once again.
Can hydrangeas grow indoors?
Yes and no. Oftentimes greenhouse-grown potted hydrangeas are given as springtime gifts that can be kept indoors, but it can be tricky to maintain them. For example, an indoor hydrangea plant can be finicky; It will be happiest in a room between 50 and 60 degrees Fahrenheit, but unhappy in warmer spaces. It might be best to plant your potted hydrangea outdoors in your garden for best results.
How can I change the color of my hydrangeas?
You can change the color of your hydrangea flowers by tinkering with the soil pH. Change blue flowers to pink flowers by decreasing the acidity of your soil. Do this by adding hydrated lime to the soil in the spring. To change pink flowers to blue flowers, increase the acidity of the soil. Do this by adding aluminum sulfate to your soil in the spring. Color-change does not happen immediately, it can take a while for the plant to acclimate itself to adjustments to soil pH.
How can I tell if my hydrangea blooms on new wood or old wood?
These terms can be confusing, which often leads to pruning off the woody stems that could hold the buds for next season's blooms. Make a note of the type of hydrangea you have, when it blooms, and the best pruning practices for the plant. If your hydrangea flowers in the early summer, you have a plant that blooms on old wood (previous year's stems). If your hydrangea flowers mid- to late summer, you have a plant that blooms on new wood (the current year's stems).
Can I train a hydrangea shrub to grow into a flowering tree?
Yes, you can train a hydrangea shrub into a small flowering tree with a single trunk, but be patient because the process can take a few seasons to complete. Many gardeners prune limelight hydrangeas into trees because they grow to just the right height for an ornamental tree. In addition to limelight, there are other types of tree hydrangeas (Hydrangea paniculata) that are easy to train into ornamental trees.
Watch Now: How to Prune Hydrangeas
“Hydrangea." North Carolina State University Extension Office.
"Hydrangeas in the Garden.” Rutgers.Edu.