How to Grow Hydrangeas
By: Julie Day
Blue hydrangeas make an eye-catching addition to any landscape.
By early- to mid- summer, the large flower heads of hydrangea (Hydrangea sp.) begin to dot the landscape, weighing down the branches with saturated color. Hydrangeas make a great addition to landscape borders, and the blossoms are gorgeous as cut or dried flowers. Here are some tips for growing this eye-catching plant in your yard.
Pink mophead blossoms look like pompoms.
Hydrangeas are deciduous shrubs that transform from bare winter stalks into lush, green branches dripping with blooms in summer. These graceful, rounded shrubs range from 3 to 10 feet tall or more. Larger varieties look more treelike and substantial in shrub borders, while smaller varieties can be tucked into perennial beds or even containers.
Colors of blossoms include white, pink, lilac, red, blue, purple, and even greenish. Blossom color can change as the flower matures, or as the plant itself matures, and it’s not uncommon to see more than one color on one plant (or even within one blossom!). You can also change the color of many hydrangeas using soil supplements, as explained below.
There are more varieties of hydrangea than people can agree upon, but most garden hydrangeas fall within a few main species:
- Bigleaf hydrangeas (Hydrangea macrophylla) include the familiar “Mopheads” and “Lacecaps” that are used in cut flowers and florists’ arrangements. Hardy to zone 6.
- Climbing hydrangeas (Hydrangea anomala) are hardy to zone 4 with white, lacecap-style blooms. They can be trained to grow up trellises or spill over walls.
- Oakleaf hydrangeas (Hydrangea quercifolia) are native to the U.S. They have a distinctive peeling bark and spectacular red fall foliage. Hardy to zone 5.
- Panicle hydrangeas (Hydrangea paniculata) boast late-season, pale pink to lime green blossoms. They are the most cold hardy variety, reliable to zone 4.
- Smooth hydrangeas (Hydrangea arborescens) are another native U.S. plant and hardy to zone 4.
Hydrangeas make a stunning border shrub.
If a hydrangea doesn’t bloom, chances are it isn’t planted in the right spot. While some varieties tolerate more or less sunshine than others, in general hydrangeas do well with:
- Light: Full morning sun, with some light afternoon shade.
- Soil: Rich, crumbly, well-draining soil with plenty of organic matter.
- Water: They don’t have the word “Hydra” in their names for nothing! Choose a location with plenty of water and good drainage. Hydrangeas are thirsty plants, but they don’t like to sit in water.
Oakleaf hydrangea exhibit dramatic red foliage in the fall.
When planting or propagating hydrangeas, keep in mind that:
- Early summer is a great time to plant hydrangeas, but they are more readily available when blooming. Plant anytime throughout the growing season, although they will need TLC in hot weather.
- Use lots of organic matter in the planting hole, especially if you have clay soil.
- Make sure your hydrangea is planted at the same depth it was in the pot.
- Hydrangeas can be propagated using softwood cuttings on an existing plant. Choose a nonblooming, new, soft green stem, and take a 6”- 8” cutting with several pairs of leaves. Remove the bottom leaves, dip in rooting hormone, and plant in light compost. Create a mini-greenhouse using glass jars or plastic. Place in a bright, shady spot, and keep moist until rooted. Transplant carefully into light, rich soil.
- Hydrangeas can also be propagated by burying a live branch in a technique known as ground layering.
Hydrangeas need rich soil and plenty of water
Caring for Hydrangeas
To keep your hydrangeas healthy, remember to:
- Fertilize 2-3 times throughout the growing season with a balanced, slow-release organic fertilizer.
- Keep hydrangeas mulched to hold in moisture. Organic mulches will also break down to enrich the soil.
- Hydrangeas become visibly wilted if allowed to dry out. They need at least an inch of water per week during the growing season, and possibly more in hot, dry weather.
- Deadheading promotes more blooms, although some gardeners like to leave the dried blossoms on the stalks during the winter.
- New growth can be cold sensitive. Protect your hydrangeas from late spring freezes, and don’t fertilize or prune in the fall.
Hydrangea blooms come in a wide variety of colors.
Pruning techniques for hydrangeas vary depending on the variety:
- Bigleaf (H. macrophylla) and oakleaf (H. quercifolia) hydrangeas bloom on buds that emerge from old wood. In spring, only remove stalks you’re certain are dead. Heavier spring pruning will result in lots of new stems that won’t bloom until next year. After they bloom in summer, you can prune lightly for shape, and also thin the stalks – if desired – to encourage fewer, but larger, blooms.
- Panicle (H. paniculata) and smooth (H. arborescens) hydrangeas bloom on new growth, so they can be pruned in early spring to encourage a flush of new stems for summer blossoms. Some gardeners prune smooth hydrangea to the ground in the late fall and treat them as a perennial.
Bloom color varies even within the same plant.
Changing the Color of Hydrangea Blooms
The color of pink and blue hydrangeas depends on the amount of aluminum within the plant, which is controlled by soil pH. Acid soil (plus aluminum) makes the flowers blue, while alkaline soil turns them pink.
Gardeners love to manipulate this by adding supplements to achieve a desired flower color. Each variety reacts differently to color manipulation, and white varieties usually won’t change color at all.
Drying Hydrangea Blooms
Hydrangea blossoms make lovely dried flowers. Leave them on the plant until they are papery-feeling and partially dry. Carefully cut the stems and hang the flowers upside down, or stand them in a jar, until completely dried.
- When to Prune Hydrangeas (article)
- Hydrangea Questions and Answers (U.S. National Arboretum)
- Hydrangeas! Hydrangeas! (website on Hydrangeas)
- Hydrangea Propagation by Ground Layering (video)