How to Grow Hydrangeas

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Hydrangeas (​Hydrangea​ spp.) are perennial flowering shrubs best known for large blooms in shades of blue, purple, pink, white, green and red. The best-known variety grows around 6 to 10 feet tall and grows globe-shaped flowers about 6 inches wide from summer through fall. There are also hydrangeas that grow anywhere from 2 to 15 feet tall, so there's a hydrangea that's just perfect for your garden. No matter what variety you choose to grow, these plants are easy and fun to grow and are sure to leave you with ample blooms for months at a time.

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Best Uses for Hydrangeas

One of the greatest things about hydrangeas is their versatility. There are climbing varieties that grow on walls and creep along as ground cover, dwarf varieties perfect for containers, treelike varieties and even bushy varieties that make excellent hedges.

Hydrangea "flowers" are actually large flower clusters that are made up of a large group of star-shaped blooms. They come in a variety of sizes and shapes, most famously:

  • Mophead:​ The most famous type of hydrangea flower, these are large, round clusters of flowers.

  • Lacecap:​ A fascinating blend of large and small blooms, these have centers made of small blossoms and edges adorned with larger flowers, like those seen on mopheads.

  • Cone:​ These cone shapes are usually the size and shape of a football.

Hydrangea flowers are stunning both on and off the plant; in fact, they are quite popular in wedding floral arrangements. Interestingly, many hydrangeas change colors as they age, and other species have different hues depending on the soil pH.

Give careful consideration to the location of your hydrangea plants, as they require plenty of room to grow. Though many varieties do well in partial and full shade, it is best to avoid planting under trees since the competition with the roots can prevent the plants from thriving. Also, avoid growing these in windy areas, as their stems can snap easily. Finally, take care when planting in areas with pets or children because the leaves and flower buds are toxic to dogs, cats and humans.

How to Grow Hydrangeas

  • Common Name:​ Hydrangea
  • Botanical Name:​ ​Hydrangea​ spp.
  • When to Plant:​ Spring or fall
  • USDA Zones:​ 3-9
  • Sun Exposure:​ Varies by species and location, but almost all do well with partial shade
  • Soil Type:​ Well-draining soil that is slightly acidic and rich in organic matter
  • When it's in Trouble:​ Pests on foliage or stems, failure to bloom, spots on leaves or flowers
  • When it's Thriving:​ Large green leaves and large clusters of flowers that bloom from summer through fall depending on the species

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Starting Hydrangeas From a Seedling

Dig a hole approximately twice as wide as the nursery container and equally deep. This should provide plenty of room for the roots to spread. If you plan to plant more than one hydrangea at a time, space them at least 3 feet apart but check your plant's specific recommendations; this will vary by cultivar since dwarf varieties will not need as much spacing as plants grown as hedges.

Mix the soil you have removed from the hole with bone meal and 10 to 15 percent organic matter, such as compost or mulch. For potted plants, add sufficient drainage material at the bottom of the container and use a potting soil that contains lots of peat moss, perlite or vermiculite.

Remove the seedling from the container and gently loosen its roots, taking care to free any bound or twisted roots before setting it in the hole. The crown should be positioned slightly higher than it was in the nursery container. When the plant is positioned just right, backfill the hole with your amended soil and then water thoroughly. Add a 2- to 3-inch layer of mulch around the roots, taking care to keep it at least 2 inches away from the crown.

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In What Zone Do Hydrangeas Grow Best?

There are hydrangeas that can grow in zone 3 all the way through zone 9, but the classic bigleaf hydrangea is best suited to zones 6 through 9. For cooler zones, look for panicle or smooth hydrangea varieties.

When Should You Plant Hydrangeas?

Hydrangea-planting season varies based on the variety and the region in which they are grown, so the best time to plant these flowers is generally when you see them available at your local garden center. They should usually be planted in late spring or early fall in areas with cool winters in order to avoid the threat of frost as well as peak summer heat. In warmer areas where it doesn't snow, though, they may be planted all the way from midfall through early spring.

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Soil, Sunlight and Water Recommendations for Hydrangeas

Hydrangeas require rich, well-draining, slightly acidic soil. Interestingly, some species actually change color based on the pH level of the soil. When the soil pH is between 5.0 and 5.5, they tend to be more of a blue shade, and they will be more of a pink or purple shade in more alkaline soil with a pH between 6.0 and 6.5. When grown in soil with a pH between 5.5 and 6.0, they will either grow purple or have a combination of pink, blue and purple hues.

If you want to guide the flower color, test your soil and amend its pH before planting. You can slowly and safely increase acidity by adding aluminum sulfate or coffee grounds and decrease it by adding garden lime or ground eggshells. Retest before planting. After you have planted your hydrangeas, if you want to maintain the same colors, you'll need to test the soil annually and amend it accordingly, starting in late summer and continuing the process through the following spring.

A hydrangea's sunlight needs will vary based on the species and your region. In southern regions, most hydrangeas will only tolerate a few hours of morning sun; in northern regions, they may tolerate full sun. In areas in between, it's best to provide afternoon shade to ensure they are at least protected from harsh midday sun. Hydrangeas that are grown in shade tend to grow larger, but many species still require at least a few hours of sunlight.

Hydrangeas are water lovers, and their name actually means "water vessel." Needless to say, they are not drought tolerant, and their soil should be kept consistently moist (but never wet). The warmer your region, the more sun they get, and the larger their leaves, the more water they will need. Maintain a 2- to 4-inch layer of mulch to help seal in moisture and stifle weed growth. Fertilize plants with a slow-release 10-10-10 fertilizer in early spring as soon as new growth appears and again in late spring.

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How to Propagate Hydrangeas

In early summer, take 5- to 6-inch cuttings from flowerless branches. Strip away bottom leaves and cut full-size leaves in half. Use a powdered rooting hormone according to the package instructions to stimulate growth. Place cuttings in a pot with sterile potting soil and water thoroughly before covering with a clear plastic bag to seal in moisture.

Place your pot in an area with bright, indirect light. Check the soil every few days, adding water when it begins to dry. After three weeks, give the stems a light tug to ensure roots have begun to form. Keep the cuttings indoors during their first winter before replanting in their final home the following spring.

How to Harvest Hydrangeas

For cut flowers, use sharp pruners to clip flowers from the bushes. To preserve the flowers, though, harvest at your preferred color stage and begin the drying process immediately. Alternatively, you can leave the flowers on the plant until they naturally dry on their own, but the colors will fade a little, and the petals may be more brittle than flowers dried through other methods. Keep in mind that some varieties need to be deadheaded to promote new bud growth.

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How to Prune Hydrangeas

Hydrangeas do not require a lot of pruning, but they should be pruned periodically to improve their appearance and increase airflow and sun exposure. That said, the method and timing of pruning varies based on your specific species; some species only bloom on old wood, while others only bloom on new wood.

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Because hydrangeas that bloom on old wood start growing flower buds in fall, these need to be pruned in late summer after the flowering stage ends and before new buds start to grow. This group includes bigleaf, oakleaf, climbing and mountain hydrangea varieties. Never prune this group in winter unless you are removing dead, diseased or broken branches. Only prune as necessary since this group should not be subjected to heavy pruning.

Hydrangeas that bloom on new wood include smooth and panicle varieties. These should only be pruned in late winter or early spring just as new leaves are beginning to show. Cut branches just above a node, removing one-half to one-third of the old branches as well as all weak, dead, broken, diseased and spindly branches.

For smooth hydrangeas, light pruning will encourage plant growth, leaving you with large shrubs that have many small flowers. Heavy pruning to under 1 1/2 feet tall will leave you with smaller plants with fewer flower heads that will be notably larger. For panicle hydrangeas, cut out small branches and leave larger stems.

Common Pests and Other Problems for Hydrangeas

Hydrangeas are largely resistant to pests but may become infested with aphids and mites. Oakleaf varieties occasionally have issues with Japanese beetles. All of these pests can be identified visually and treated with insecticidal soap.

Occasionally, growers have problems with plants failing to bloom. This is most common in hydrangeas that grow on old wood and is usually a result of pruning at the wrong time, frost damage, excessive fertilization or too little light.

Common Diseases for Hydrangeas

Just as they're mostly resistant to pests, hydrangeas are rarely affected by disease. Occasionally, they may have issues with bud blight, bacterial wilt, leaf spot or powdery mildew. Bud blight appears as reddish-brown blotches on petals. Bacterial wilt and leaf spot both appear as brown discolorations on the leaves. Powdery mildew looks like white fuzzy spots on the foliage of the leaves.

All of these diseases can be avoided by preventing overly moist and humid conditions. Only grow hydrangeas with proper spacing and in areas with good drainage. Try to only water the ground around the hydrangeas and avoid getting water on the leaves or flowers. Ideally, water them in the morning so the sun and warm air can dry any water splashed on the leaves or flowers throughout the day. Prune as necessary to allow for proper airflow and light penetration.

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references

Jill Harness is a blogger with experience covering architecture, design and decor trends from around the globe. As she lives in what would politely be called a "fixer upper," she is particularly interested in writing about DIY projects and repairs. Most of her home design writing can be found at www.homesandhues.com. You can find out more about Jill's experience and learn how to contact her through her website, www.jillharness.com.