Hydrangea Care Guide


Hydrangeas add a vibrant splash of color to a garden. Need help growing them?
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If you’re looking for a flowering shrub that ticks all the boxes – easy care, long bloom time, large beautiful flowers in a variety of colors – hydrangeas are the way to go.

Shrubs in the landscape provide structure and framework. They can be used as a privacy hedge or to conceal an eyesore. Flowering shrubs transform utility into beauty, and few are more stunning than hydrangeas. They produce large, beautiful blooms throughout the summer, and dried flower heads can last into the winter.

These shrubs, which are native to North America and Asia, are known as hortensias. The popularity of these beauties has grown in recent years, and breeders are constantly developing new varieties.

Hydrangeas are extremely simple to grow. They are not picky about soil, require little water and fertilizer, and require little pruning. However, selecting the appropriate type for your garden is critical.

Types of Hydrangeas

Hydrangea types are divided into three categories: those that bloom on old wood, those that bloom on new wood, and those that bloom on both new and old wood. Knowing you’re your hydrangea blooms is important because it affects when or if you should prune.

Old Wood Bloomers

These bloom on what we call “old wood.” These are the stems that the plant made in past years. Flower buds are set at the end of the current growing season on these older stems and will bloom next year.   Old wood hydrangeas really shouldn’t be pruned at all.

This category includes Bigleaf or French varieties, Climbing varieties, Mountain Varieties, and Oakleaf Varieties. 

A hydrangeas flower with a gradient purple color

New Wood Bloomers

These hydrangeas create flowers on stems that grew during the current year. They bloom in the summer, so prune them late winter or early spring.

New wood bloomers include Smooth and Panicle hydrangea varieties

Rebloomers or Remontant Types

These shrubs bloom on both old and new wood. You can expect a burst of flowers early in the summer (blooming on old wood) and another burst in late summer/early fall (blooming on new wood). Size and flower shape varies depending on the cultivar. Look for Endless Summer and Bloomstruck.  

Buying a Hydrangea

When you go to the nursery or garden center to buy a hydrangea, look for a plant with strong top growth, without crossed or broken branches. 

You can tell that it has been well cared for by moist soil and robust leaves. There should be no wilting or browning, and no leaf spots. 

Ask an employee for assistance if you want to inspect the roots. Do not remove the plant from the container on your own. You can potentially harm the plant.

Consider the mature size of the variety you wish to plant. Be sure to give it room to reach its full, beautiful potential. Read the plant tag! It provides a lot of good information.

Colorful and beautiful bush of hydrangeas flowers in a park

Caring for Your Plant

Cultural Considerations

Most hydrangeas are hardy in USDA zones 5 to 9. You might be able to grow them in Zone 4 if they are in a sheltered location and well mulched in winter. Grow the new wood bloomers or reblooming types in zones 4 and 5 because old wood flower buds will freeze in very cold weather.

Sunlight

Hydrangeas prefer a partial shade location. Give them a spot where they can enjoy the morning sun and have shady protection in the afternoon. This is why I recommend planting them on the east side of your house. 

They may not flower as well if they do not receive enough sunlight. Similarly, flower production may suffer if plants are exposed to too much sunlight. Furthermore, excessive sunlight can scorch leaves and cause the plant to wilt during hot afternoons.

Nutrients

Hydrangeas grow best in moist, well-drained soil that is rich in organic matter. They are not picky about pH, but pH can affect flower color.

Hydrangeas don’t require a lot of fertilizer. All they require is an early spring application of a balanced slow-release fertilizer. In the fall, use compost or leaf mold as a top dressing to keep the soil rich.

Water

Make sure these shrubs have additional water during dry spells. They prefer about 1 to 2 inches of water per week, either from rainfall or a garden hose.

Assorted colors of hydrangeas flowers blooming in a garden

When to Plant 

Hydrangeas can be planted in spring after the danger of frost has passed and in the early autumn, about 4 to 6 weeks before your area’s first frost date. Planting in summer can be done, of course, but the heat of summer may be too stressful for these shrubs to get off to a good start.  

Plant on a cool day, either early morning or late afternoon. The ideal situation would be to plant on a cool, cloudy day.

A layer of mulch around your newly planted hydrangea helps hold moisture in the soil and can help prevent transplant shock and wilting. 

How to Plant 

Dig a hole about two times as wide and as deep as the root ball of your new hydrangea. The crown of the plant (where the roots and the stems meet) should be level with the top of the soil.

Remove the plant from the pot and gently untangle any circling roots.

Place the plant in the hole and fill it in around the roots with the excavated soil. 

Some planting guides may recommend amending the soil with plenty of organic matter, but that only creates a “flower pot” effect. The plant’s roots will stay in the amended soil and won’t grow further out. If you’re amending the soil, add the organic matter to the top of the area you plan to dig up. This allows the amendments to mix with the soil and become part of it.

Firm the soil around the plant and water it in. Add 2 inches of mulch around the base of the plant out to the root line. Be careful not to pile the mulch on the crown of the plant.

Monitor your new shrub’s water needs carefully during its first year. And that’s all. Don’t fertilize and certainly don’t prune – unless you need to remove a broken branch.

Pruning Hydrangeas

This topic gives many gardeners a lot of angst. Hydrangeas usually don’t need pruning, and it’s very easy to remove the flower buds accidentally. After freezing temperatures, improper pruning is the biggest reason a gardener may have problems having their hydrangeas bloom.  

If you must prune, remember that “old wood” hydrangeas should be pruned shortly after they flower, at the end of the summer. “New wood” hydrangeas can be pruned at the end of the growing season or in early spring.  

See our article on pruning hydrangeas for more specifics.

A gardener trimming the stems of a dried hydrangeas flower

Pests and Diseases

Aphids and spider mites may take up residence on your hydrangeas. These shrubs can weather a small infestation, so keep an eye on your plants throughout the growing season. If your garden has a population of beneficial predatory insects, they will do the pest control work for you. Insecticidal soap can also be used. Follow the instructions on the bottle carefully.

Powdery mildew, botrytis blight, and Cercospora leaf spots are fungal diseases that can be avoided with proper spacing at planting time and watering practices that allow the foliage to dry quickly. Water early in the morning, and don’t water from overhead. Foliage that is wet for several hours invites diseases. 

Root rot can occur if the soil is too saturated and does not drain well. Water only when the top 4 or so inches is dry. 

Wilt can occur on hot summer afternoons, especially with bigleaf hydrangeas. Don’t assume the soil is dry and the plant needs watering! Sometimes plants wilt even when there is adequate soil moisture. They do this as a protective mechanism and will perk back up when the temperatures cool.

Propagation 

Hydrangeas do not produce viable seeds easily. It’s better to propagate hydrangeas from either stem cuttings, layering, or root divisions.

If you’re interested in trying this out, make sure to check out our article on propagating hydrangeas. 

Stem cuttings of a hydrangeas plant propagated in a small pot

Changing a Hydrangea’s Color

Can you really change the color of your hydrangea? Well…sometimes. Flower color is dependent on the cultivar, cultural conditions, and soil pH. 

Hydrangea macrophylla and hydrangea serrata produce flowers whose colors are influenced by soil pH. In acidic soils, the flowers are blue, and in alkaline soils, the flowers are pink. Adding lime or alum to the soil can change the flower color from blue to pink or pink to blue, but white flowers will always be white.

While the results are not long-lasting and probably more successful with hydrangeas planted in containers than in the ground, it’s a fun thing to try. 

Be aware that the natural mineral content of your soil and groundwater and rainwater all contribute to a soil’s pH. While you may have succeed in changing the pH temporarily, keeping it changed is impossible.  

  • First, conduct a soil test to determine if your soil has a low pH (acidic) or a high pH (alkaline).
  • If you have acidic soil and want to try to turn the flowers pink, add garden lime to the soil in March, April, and May. Mix 1 tablespoon of hydrated lime in 1 gallon of water.
  • If you have alkaline soil and want to try to turn the flowers blue, use aluminum sulfate, also during the spring months.
  • Drench the soil with the mixture. Be careful not to get it on your skin, clothing, or on the leaves of the plants. 

These drenches can also be used to intensify the existing color of the flowers. For example, adding a lime drench to an already pink hydrangea can make the color more vivid.

Were you successful in changing your hydrangea’s flower color? Let us know!

Alaine Connolly
Alaine has been working way too hard in horticulture since 1992, beautifying golf courses, resorts, and hotels. She is a part time landscape designer who works full time caring for a 28,000 square foot public garden. At home, she maintains her own 400 square feet plot. Alaine lives in northern Illinois - zone 5b.
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