Questions Answered Series: Hydrangeas

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Your Questions on Hydrangeas, Answered!

Hydrangeas have come to be a fan favorite in the gardening world. Blooming in hues of blue, pink, white, and even green, the array of colors keep us coming back for more, time and time again. There’s virtually a hydrangea for every garden! Whether they stand alone or are planted in a hedge, these shrubs know how to make an impact. We often hear that gardeners are intimidated by this popular flowering shrub. We’re here to tell you; you don’t have to be. Whether you’re already growing hydrangeas or are planning to buy some soon, we’re here to help you find all the information you need to know, and we’ll help bust some myths along the way! See our most common questions about hydrangeas and learn how to enjoy them year-round in your garden.

Field of hydrangea hedges

What are the different types of hydrangeas?

Here at Great Garden Plants, we offer 7 different types of hydrangeas. Knowing which type you have is one of the most important steps to growing them successfully! We’ll spell it all out for you right here:

  1. Bigleaf hydrangeas (H. macrophylla): these hydrangeas are characterized by their big, glossy, leathery leaves and pink, blue, or purple blooms.
  2. Mountain hydrangeas (H. serrata): native to chilly mountainous areas, mountain hydrangeas grow well in colder climates. They look similar to bigleaf hydrangeas, with pink, blue, or purple blooms, but they’re generally lacecap instead of mophead.
  3. Smooth hydrangeas (H. arborescens): beloved for their huge, globular blooms and rock-solid reliability. Sometimes called ‘Annabelle’ -type hydrangea, as this variety is the most widely recognized smooth hydrangea.
  4. Oakleaf hydrangeas (H. quercifolia): easy to recognize with their big, oak-shaped leaves and fragrant white flowers. One of the few hydrangeas with fall foliage color.
  5. Panicle hydrangeas (H. paniculata): one of the most beautiful, reliable, and long-blooming hydrangeas ever. Football-shaped flowers start white and change to pink or red in late summer. Sometimes called peegee or ‘Limelight’ hydrangea.
  6. Cascade hydrangeas (H. x): white flowers bloom along trailing stems, creating a cascading display of flower power. One of the newest types of hydrangeas on the market.
  7. Climbing hydrangeas (H. petiolaris): grows as a vine using rootlets to grab ahold of structures. Popular on chimneys, brick, and wood fences.

How do I grow hydrangeas?

Soil: Hydrangeas require well-drained but moist soil. A good layer of mulch is very helpful for minimizing drought stress and conserving moisture.
Light: Plants can take sun (6+ hours sun) in cooler areas, but part sun (4-6 hours sun) with afternoon shade is recommended in warm climates. If your plant frequently wilts in the afternoon even though it was recently watered, or your flowers turn brown quickly, that may indicate the spot is too sunny for it.
Water: Average to abundant (as long as the soil is well-drained).
Winterizing: Apply a good 2-3″ layer of mulch to help protect the shallow roots.
Fertilizing: Fertilize in early spring, once the ground has thawed, with a granular rose fertilizer. For reblooming varieties, make an additional application in late spring/early summer to boost reblooming ability, particularly in colder areas.

Which hydrangeas bloom on old wood vs. new wood?

Knowing whether your hydrangea blooms on old wood vs. new wood is important when determining when to prune. Why? It distinguishes when your plant sets buds, and we want to avoid cutting off any precious future flowers.

Bigleafmountaincascadeclimbing, and oakleaf hydrangeas all bloom on old wood, which means they create their flower buds for the next year right when they finish blooming in the current year. That means flower buds sit on the plants all year long, just waiting for summer.

Panicle and smooth hydrangeas bloom on new wood, which means they create their flower buds in early spring after dormancy. Buds are set on the newest growth on the plant, and usually don’t wait too long before bursting into bloom.

How and When Should I Prune My Hydrangeas?

How and when you prune your hydrangeas depends on two things: which type of hydrangea you have and whether it blooms on old or new wood. If you’re not sure which type you have, don’t worry, we spell it out for you in the questions above. Here’s how to prune each type:

  1. Bigleaf hydrangeas (H. macrophylla)avoid pruning bigleaf hydrangeas, as they bloom on old wood, which means pruning it will cut off next year’s flower buds. You can trim off any dead wood or old blooms, but nothing more!
  2. Mountain hydrangeas (H. serrata)don’t prune mountain hydrangeas. Similar to bigleaf hydrangeas, they bloom on old wood. For maximum flower power, avoid trimming any part of the plant, except for dead branches and spent flowers.
  3. Smooth hydrangeas (H. arborescens)prune smooth hydrangeas in late winter or early spring by cutting back 1/3 of their total height. They bloom on new wood, so this will encourage lots of new growth, which means lots of flowers.
  4. Oakleaf hydrangeas (H. quercifolia)avoid pruning oakleaf hydrangeas, as it will remove the flower buds for the upcoming season. It blooms on old wood and should only be pruned to remove dead branches and old blooms.
  5. Panicle hydrangeas (H. paniculata): panicle hydrangeas bloom on new wood, so they should be pruned in late winter or early spring by cutting back 1/3 of their total height. This will promote stronger stems, bigger buds, and more flowers.
  6. Cascade hydrangeas (H. x): no need to prune cascade hydrangeas, as they bloom on old AND new wood! You’ll get the best performance if you avoid pruning.
  7. Climbing hydrangeas (H. petiolaris): climbing hydrangeas bloom on old wood, so they flower best if you do not prune them.

Which Hydrangeas are easiest to grow?

While some hydrangeas are notorious for being picky, other types are known to be a breeze (even for beginners). By far, the easiest hydrangeas to grow are panicle hydrangeas (Hydrangea paniculata). They’re hardy, reliable bloomers, and adaptable to a wide range of growing conditions. Enjoy months of blooms without a worry in the world!

If you’re looking for an alternative to panicles, then smooth hydrangeas are a great second option.

Can hydrangeas grow in pots?

Yes, hydrangeas grow well in large containers! There are three important things to keep in mind when planting hydrangeas in pots:

  1. Proper drainage. Hydrangeas like water, but still require well-draining soils. It’s vital that the pot or container has large drainage holes to prevent standing water.
  2. Pot size. It’s important you select the right size pot when growing shrubs in containers. A pot that is too large will hold on to water for too long, while a pot that is too small will dry out quickly.
  3. Lighting. Place your pot in an area that receives full sun (6+ hours direct sunlight) to part sun (4-6 hours direct sunlight).
hydrangea Tuff Stuff in a garden patio landscaping

Can I trim my hydrangea to keep it small?

No, we do not recommend trimming hydrangeas to keep them small for a variety of reasons. Cutting your hydrangea back severely can cause weak stems and reduced blooms, especially if it is a variety that blooms on old wood! Instead, we recommend choosing dwarf varieties. There are many to choose from, including Little Lime®Bobo®, Invincibelle Wee White®Invincibelle Garnetta®Invincibelle Mini Mauvette®Fire Light Tidbit®Tiny Tuff Stuff™Wee Bit Grumpy®, and more.

Which hydrangea do I have?

There are so many types of hydrangeas on the market, it’s hard for us to tell without seeing them with our own eyes! We summarized the most notable features for each type (with pictures) in the answers above and in our “7 Different Types of Hydrangeas” blog. If your plant is still a mystery, you can always send us pictures on social or via email at info@greatgardenplants.com.

Should I deadhead my hydrangeas?

It’s completely up to you! Some gardeners like to trim them off as soon as they fade, while others keep them around for extra color and texture in the winter months. Either way, all spent flowers should be removed in spring before new growth emerges.

Hydrangea covered in a blanket of snow

Which hydrangeas change color?

Almost every type of hydrangea changes color in some way throughout the season. Most notably, bigleaf hydrangeas (H. macrophylla) and mountain hydrangeas (H. serrata) are known to change from pink to blue or purple depending on the soil pH and availability of aluminum ions.

Panicle hydrangeas (H. paniculata) typically start the season with light green blooms, which turn white and take on bright pink and dark red hues as they age. Smooth hydrangeas (H. arborescens) typically do the opposite, starting white or pink and turning jade green as they mature. Some oakleaf hydrangea (H. quercifolia) blooms change color, but most notably, their foliage takes on vibrant fall colors.

How do I make my hydrangea blue or pink?

We’ll keep this chemistry lesson as short as possible! The color of bigleaf hydrangeas (H. macrophylla) depends on two things: the soil pH and aluminum ion availability. In basic soils (pH 7.5 or higher), aluminum is immobile in the soil and cannot be reached by plants. This results in flowers that bloom pink. However, when the soil is acidified (pH 6.5 or lower), the aluminum ions are released from the soil and can be taken up by the plant. The more aluminum hydrangeas take up, the bluer their flowers will be. If your bigleaf hydrangea in acidic soil is still not blue, that may mean your soil has a low aluminum ion concentration.

How do you change your soil pH? In general, we don’t recommend altering your soil pH. We think every hydrangea color is beautiful, but we are biased hydrangea lovers! If you do want to change your bloom color, we’d recommend using ground lime to raise the pH (pinker blooms), or garden sulfur or ammonium nitrate to lower the pH (bluer blooms). The easiest way to do this is in a container, so consider planting your hydrangeas in pots instead of beds. Make sure you test the pH and aluminum content before altering your soil. Finally, be patient! You may not see results until the following season.

Great garden myths: using vinegar, rusted nails, razor blades, hairpins, coffee grounds, pine needles, are not practical ways to change your hydrangea color. Stick with our recommendations above, or ask your local nursery, garden store, or favorite online plant store (info@greatgardenplants.com) for alternatives!

hydrangea blossoms with pink to purple in one blossom

Are hydrangeas poisonous to dogs and cats?

The ASPCA does list hydrangeas as toxic to dogs, cats, and horses. While it won’t cause death, it will upset your pet’s digestive system when ingested. However, it won’t cause problems if they touch it, brush up against it, or even roll on it. Keep an eye on your pets as they play near your hydrangeas and train them to avoid chewing on them.

Why aren't my panicle hydrangea flowers turning from white to red?

Panicle hydrangeas are glorious in the fall, taking on rich pink and red hues as the flowers age. Some gardeners note that their panicle hydrangeas are missing their colorful show, turning from white to brown instead. There are two reasons why this might happen: water stress and high temperatures.

If your hydrangea is stressed in late summer, it’ll probably save its energy and skip this year’s colorful show. It takes energy to have pigmented blooms, so your plant has to use it wisely. Make sure you keep your hydrangeas well-watered throughout the summer (but not overwatered) for the best performance.

Unfortunately, we can’t control the temperature. But if we could, we would send you cool nighttime temperatures starting in late summer. That’s what triggers your hydrangeas to develop the most vibrant colors! If it’s been especially warm in your area in late summer and early fall, your hydrangea flowers might turn brown.

red cone-shaped Zinfin Doll hydrangea blossoms

Are hydrangeas evergreen?

No, hydrangeas are deciduous shrubs that lose their leaves each winter, even in warm climates. You can expect the leaves to yellow before dropping in late fall.

Why isn't my hydrangea flowering?

There are a few reasons why your hydrangeas may not bloom:

  1. Improper pruning. Have you been cutting your plants back at all? If so, when? These are usually the first questions we ask gardeners when we hear their hydrangeas aren’t blooming. Bigleaf, mountain, and oakleaf hydrangeas bloom on old growth, which means they should not be pruned. Panicle and smooth hydrangeas bloom on new growth and should be pruned in late winter or early spring. Pruning at the improper time (or at all) will cut off the flower buds.
  2. Not enough light. If your hydrangea is growing in low light, blooming may be reduced or stop overall. Ensure your hydrangeas are receiving sun (6+ hours of direct sunlight) or part sun (4-6 hours direct sunlight).
  3. Cold winters. This is mainly a problem for hydrangeas that bloom on old wood (bigleaf, mountain, oakleaf, cascade, climbing). Because these hydrangeas have flower buds on them all through fall, winter, and spring, they can be damaged by cold weather, especially in zones 5 and 6. If new growth on your plant in spring emerges from the ground – not the stems – then winter cold is killing the branches back to the ground. We suggest moving them to an area protected from winter winds
  4. Spring frost. This can threaten hydrangeas in nearly all areas, including warm climates. If a spring frost or freeze hits, it zaps the bud, and the flower buds for the year die. Fortunately, this is pretty easy to protect from – on nights when a frost or freeze is predicted, drape old blankets over the plants.
  5. Too much fertilizer. An excess of nitrogen fertilizer encourages your hydrangeas to grow leafy green growth instead of flowers. Make sure you are providing your hydrangeas with a well-balanced fertilizer.
  6. Deer. Deer are fond of feeding on hydrangea flowers, so if deer are a problem in your area, you may need extra protection!

When should I transplant my hydrangeas?

In general, spring and fall are the best times to transplant hydrangeas. For gardeners in the north, spring is the best time. It will give your shrubs three seasons to establish in their new home before winter hits. For gardeners in the south, it’s the opposite. We suggest transplanting your hydrangeas in the fall, as summers tend to be more stressful than winters. Your shrubs will have three seasons to grow more roots before hot and dry summers arrive.

Can I cut hydrangea flowers for arrangements?

Yes, of course! Hydrangeas are lovely additions to floral arrangements. The key to keeping healthy cut flowers is water, right from the start. Bring a container of slightly warm (or tepid) water with you as you pick flowers. Cut stems at a diagonal angle with sharp clippers, removes all the leaves, and place them in a vase.

While hydrangeas are known for their long-lasting display in the garden, they are notorious for fading quickly as cut flowers. Check out our blog for the best hydrangeas to use and how to keep them looking fresh! Click here for more.

A variety of hydrangea blossoms in a vase on a table

Why is my hydrangea flopping?

We love hydrangeas that develop massive blooms, but not when they flop over! Here are 3 reasons why your hydrangea may be flopping:

  1. Severe pruning. When hydrangeas are cut back severely, the plant responds by rapidly pushing out a lot of soft new growth – this happens so quickly that it doesn’t have the time to develop the strong woody cells that keep the branches upright. It’s typically temporary for that season, and if it is pruned properly the following spring, it can recover. That means cutting it back by just 1/3 its total height in late winter/early spring.
  2. Too much shade. Growing in too much shade will encourage the plant to grow tall in search of light, but with weak stems. If your plant is receiving less than 4 hours of direct sunlight a day, we recommend transplanting it to an area with more sun.
  3. Excess fertilizer. Applying too much fertilizer to your hydrangeas will encourage them to grow quickly, but with very weak stems. Make sure you are not overfertilizing your shrubs. They only need a boost once a season!

How do I create a hedge of hydrangeas?

Making your own hydrangea hedge can be intimidating, especially if you’re starting from scratch. That’s why we’re here! We’ll guide you through how to recreate the magic in our blog (linked here). Here are the main points to consider:

  • Spacing: The answer to this depends on a few different factors, including which hydrangea you’re using, where you live, and what look you’re going for. A general rule of thumb is to start by looking at the width of the plant. For example, Incrediball® smooth hydrangeas reach 5 feet wide, so you can plant them with their centers 5 feet apart.
  • Number of plants: Depends on the size of your space and which hydrangeas you use. Try using our plant calculator to help determine the number of plants for your space.

Remember, read more in our blog on hydrangea hedges!

Hydrangea hedge with large white blossoms

Are hydrangeas deer resistant?

Unfortunately, no, hydrangeas are one of the least deer-resistant plants on the market. While they only occasionally damage leaves and stems, they will certainly feast on the flowers and buds. We have yet to find a hydrangea that is truly deer resistant, so for now, you have three choices when dealing with deer: install a fence, use repellent sprays, or get a good guard dog!

Can hydrangeas grow in shade? Which hydrangeas are best for shade?

Hydrangeas grow best in full sun (6+ hours sun) in the north and part sun (4-6 hours sun) in the south. While all hydrangeas are grateful for afternoon shade in the hottest hours of the day, they do not handle full shade gardens (receiving less than 4 hours of sun). If your hydrangea is not receiving enough sun, you can expect any unhappy plant with weak stems and fewer flowers – which no gardener wants.

If you’re a shade gardener that is still determined to grow hydrangeas, we’re rooting for you! There are 2 hydrangeas that can handle shade better than others: oakleaf hydrangeas (H. quercifolia) and climbing hydrangeas (H. petioralis). They perform the best in shade, but will still have reduced blooms if they don’t receive enough sun. Keep a close eye on them and transplant to a sunnier location if necessary.

close up on cone-shaped green hydrangea blossoms

Why are my hydrangea leaves turning yellow?

Yellowing leaves typically indicates your plant is overwatered! Hydrangeas require well-draining soils and are not tolerant of “wet feet”.  Try reducing how frequently you irrigate and feel the soil before watering. If the soil feels moist to the touch, skip on watering for now. If you’re sure your plant has not been overwatered, the problem may be soil drainage.

Clay soils will hold onto water for long periods of time, suffocating the roots. Amending the soil at planting can cause poor drainage by holding onto water (we call it the bathtub effect). Landscape fabric near the base of the plant prevents soil water evaporation, keeping the soil wet for longer. We strongly discourage amending soil at the time of planting and laying landscape fabric near plants. If this is the case, you may want to relocate your plant to a new area.

Which hydrangeas can withstand cold winters?

Panicle and smooth hydrangeas are the best for cold climates, all the way down to zone 3. Because they bloom on new wood, cold winter temperatures won’t stop them from flowering. They produce their buds in the spring and bloom in the summer. While they benefit from extra mulch in the winter months, they don’t need any other protection (like covers).

While we don’t typically recommend bigleaf or mountain hydrangeas for cold climates, the Let’s Dance and Tuff Stuff series from Proven Winners includes reblooming varieties, which flower on old and new wood all along the stem. Even if some buds die back in winter, they will still flower for you in summer!

Which hydrangeas have colorful fall foliage?

Not all hydrangeas have colorful fall foliage, but the ones that do sure are a treat in the landscape. They are usually still blooming when their foliage takes on color, creating a truly unforgettable display. Here’s a definitive list of all our hydrangeas that boast fall colors:

  • Oakleaf hydrangeas are known to have the best fall color with massive leaves that take on vibrant red and maroon hues. Generally, all oakleaf hydrangeas change colors, regardless of the variety.
  • Mountain hydrangeas don’t quite take on the fall color you’d expect. Instead of turning red, orange, or yellow, they turn a rich shade of purple that perfectly compliments their light and airy blooms.
  • Let’s Dance Can Do bigleaf hydrangea is one of the only bigleaf hydrangeas that change colors in fall. Foliage takes on a mix of fiery red and deep purple hues.
  • Quick Fire is the panicle hydrangea most widely known for its fall coloration. Not only do the massive blooms turn a vibrant red or berry, but their foliage also reliably lights up the landscape.
  • Little Quick Fire panicle hydrangea is the compact version of Quick Fire. It really does take everything you love about the original (like the fall color) and packs it into a tiny habit.
  • Fire Light Tidbit panicle hydrangea also features colorful autumn foliage, turning red as the blooms change colors too.
different hydrangeas and their fall foliage

Written by: Miranda Niemiec, click here to read bio.

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