Shrub · Hydrangeaceae
Hydrangea
Hydrangea macrophylla
Give it rich, moist soil and afternoon shade, and this forgiving shrub will reward you with armfuls of summer bloom.
Partial shade
Every 3–7 days
USDA 3–9
3–10 ft · 0.9–3 m
Overview
Hydrangeas are the soft, generous shrubs that make a summer garden feel full, heaped with rounded mophead heads, flat lacecaps, or tall cones depending on the type you choose. The best known of them, the bigleaf hydrangea, is the one that turns blue in acidic soil and pink in alkaline, a happy quirk that has charmed gardeners for generations. They grow fast and bloom with real heart, reaching anywhere from 3 to 10 feet (90 cm to 3 m) across the different species.
The one thing worth knowing early is that hydrangeas don't all behave the same. Some bloom on old wood, forming their buds the summer before, while others bloom on new wood grown in the current season. That single fact shapes when you prune, whether a hard winter costs you flowers, and which types settle in best where late frosts arrive. Choose a species suited to your zone and much of the work takes care of itself.
Past the color and the pruning, there is little to worry about here. Hydrangeas simply want steady moisture, a break from the fiercest afternoon sun, and soil rich in organic matter. Give them that and you will be rewarded for years, because this is a long-lived perennial shrub that only grows more beautiful as it matures.
Care
The short version: settle it into rich, moist, well-drained soil with morning sun and afternoon shade, water deeply about once a week, and let the plant's bloom-wood type guide when you prune.
Light
Hydrangeas are happiest in partial shade, so aim for morning sun and shade through the hot afternoon. Bigleaf types especially will scorch and wilt in strong afternoon sun, while panicle types handle a good deal more of it. Deep shade is the one thing to avoid, since it thins out your flowers.
Water
The main thing hydrangeas ask for is evenly moist soil, so water deeply about once a week and more often in heat or in a pot. The name itself hints at that thirst, and bigleaf types are the first to droop when they run dry. A layer of mulch is a kind touch that holds the moisture and keeps the roots cool.
Soil
Give them rich, moist, well-drained soil full of organic matter and they will settle right in. A pH of 5.0 to 6.5 suits them, gently on the acidic side, and for bigleaf and mountain types that same acidity nudges the flowers toward blue.
Temperature
These are hardy, resilient shrubs, comfortable from about -20°F to 95°F (-29°C to 35°C) across the tougher species. The one thing to watch is a late spring frost, since it can nip the formed buds on old-wood types and cost you a season of bloom.
Humidity
Everyday outdoor humidity is plenty for a hydrangea, so there is no number to chase. Good air movement matters far more, because crowded, still, humid air is what invites leaf spot and powdery mildew.
Feeding
A balanced 10-10-10 fertilizer given a few times from spring through mid summer is all they need. A light hand is best, since too much nitrogen encourages leafy growth and holds back the flowers you are hoping for.
Pruning
Match your cuts to the bloom wood and you cannot go wrong. Trim old-wood bloomers like bigleaf, oakleaf, and mountain right after they flower and no later than August 1, and trim new-wood bloomers like panicle and smooth in late winter or early spring before growth starts.
Repotting
Hydrangeas rarely need repotting, since most are happiest planted in the ground for good. If you keep one in a container, simply move it up a size when roots circle the pot, poke from the drainage holes, or water runs straight through without soaking in.
Size & spacing
Depending on the species, hydrangeas grow 3 to 10 feet (90 cm to 3 m) tall and spread 3 to 6 feet (90 to 180 cm) wide. Give each shrub a little breathing room to fill out, so air moves freely through the branches and disease has less chance to settle.
When to plant
Hydrangeas feel at home across zones 3 to 9, so your two easy timing questions are when to plant and when to prune. Put new shrubs in the ground during the mild weather of spring or fall, look forward to bloom from late spring through summer, and let the bloom-wood type tell you the gentle moment to reach for the pruners.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Spring or fall
- Harvest: Late spring through summer; some reblooming types again in late summer
Hardiness
USDA hardiness zones: 3–9
Temperature: down to -40°C
Troubleshooting
Nearly every hydrangea worry lands in one of a few friendly categories: a plant that wilts in the heat, one that grows leaves but holds back its flowers, or foliage carrying spots or yellowing. Find what you are seeing below, learn the likely cause, and step in early so the plant stays happy.
Wilted leaves and flowers when the sun gets hot
Take a breath, because an afternoon flop is rarely serious. It usually means thirst plus too much hot sun at the same time, and bigleaf types are the quickest to sag before bouncing back once evening cools and the soil is watered. You can fix this easily: shift the plant to a spot with morning sun and afternoon shade, give it a deep drink, and tuck mulch over the roots to hold the moisture steady.
Fix:
- Water deeply to keep soil evenly moist
- Mulch to conserve moisture and cool the roots
- Site bigleaf hydrangeas where they get morning sun and afternoon shade
A healthy plant that refuses to bloom
If your shrub looks lush but shy on flowers, don't blame yourself, because timing the pruning wrong is the most common reason and it happens to everyone. Old-wood bloomers form next season's buds soon after this year's flowers fade, so a fall or spring trim quietly removes them. A harsh winter or late frost can nip the buds too, and heavy shade or extra nitrogen coaxes out leaves instead of blooms. Once you know whether yours flowers on old or new wood, you will get the timing right next time.
Fix:
- Prune old-wood bloomers only right after flowering
- Protect old-wood types from late frosts
- Reduce shade and avoid heavy nitrogen feeding
Purple-edged spots or a soft white coating on the leaves
Spots and dusty patches look alarming, but a healthy shrub shrugs them off. Cercospora and other leaf spots leave purple-edged marks with tan middles, and powdery mildew dusts the leaves white when plants are crowded and the air sits still. Both like damp, close conditions and neither is a real threat. Gather up the marked and fallen leaves, water at the base so the foliage stays dry, and thin the plant a little so air can drift through.
Fix:
- Remove and dispose of affected and fallen leaves
- Use drip or soaker irrigation to keep foliage dry
- Improve air circulation and apply a labeled fungicide if needed
Yellowing foliage while the veins hold their green
When leaves turn pale yellow but keep green veins, that is iron chlorosis, and it is an easy thing to put right. It usually shows up because the soil sits too alkaline for the plant to draw up iron, and you will notice it on the newest leaves first. Check the soil, gently ease the pH toward the slightly acidic range hydrangeas love, work in some organic matter for better drainage, and add iron only once a test confirms it is short.
Fix:
- Test and adjust soil pH toward slightly acidic
- Improve drainage and add organic matter
- Apply iron if a deficiency is confirmed
Toxicity
Hydrangeas are lovely but not for eating, and that is worth knowing before you hand a bloom to a curious pet or child. The leaves, buds, and flowers all contain cyanogenic glycosides, which can make cats, dogs, horses, and grazing animals unwell, and no part of the plant is safe to swallow. Keep clippings and fallen blooms away from pets and out of paddocks, and give your hands a rinse after pruning.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Mild
If a cat nibbles a leaf or bloom, you will likely see vomiting and diarrhea, and then a quiet, tired spell afterward. Happily, the bitter taste usually turns them away before they take in enough to cause real trouble.
Dogs Mild
Dogs are the ones most tempted to chew a branch, which tends to leave them with a sour stomach, loose stools, and a flat, subdued mood. Keep a gentle eye on a persistent chewer, since a big mouthful nudges up the small chance of cyanide trouble.
Horses Mild
A horse that grazes on hydrangea may get colic-like belly upset, diarrhea, and a dull, sluggish look. It helps to keep clippings and prunings well away from paddocks.
Rabbits Toxic
Those same cyanogenic glycosides put every part off-limits for rabbits, whose tiny size leaves them almost no wiggle room. You can expect digestive upset and weakness, so keep the plant and its trimmings out of their space for good.
Livestock Toxic
Cattle, goats, and sheep can browse enough hydrangea foliage to take in a genuinely harmful dose of the cyanogenic compound. Drooling, diarrhea, and labored breathing are the warning signs, and they mean it is time to call a vet.
Birds Caution
The leaves and buds hold the same toxin that troubles mammals, so it is best that pet and backyard birds leave them alone. If you catch one pecking at the plant, gently step in.
People Caution
No part of a hydrangea is meant for the plate, and the leaves, buds, and flowers can leave you with an upset stomach if swallowed. Keep curious little ones away from the blooms, and give your hands a good wash after pruning.
Keep clippings and fallen flowers away from pets and grazing animals; cyanide poisoning is uncommon but possible with very large ingestions.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
A handful of hydrangea species share the name yet differ in flower shape, hardiness, and bloom time. Here are the main ones worth getting to know.
Bigleaf (Hydrangea macrophylla)
This is the beloved mophead and lacecap shrub that goes blue in acidic soil and pink in alkaline, blooming mainly on old wood, though the reblooming Endless Summer types kindly flower on both old and new growth.
Oakleaf (Hydrangea quercifolia)
A friendly native with striking oak-shaped leaves and white cone-shaped panicles that mellow to pink, closing the year in warm bronze fall color and blooming on old wood.
Panicle 'Limelight' (Hydrangea paniculata)
The most easygoing of the bunch, happy in full sun and hard cold as it carries white-to-pink cone-shaped panicles on new wood, which means you prune it in late winter.
Smooth 'Annabelle' (Hydrangea arborescens)
A forgiving native that lifts up big white globe-shaped flower heads on new wood, so it takes pruning in stride and reblooms without fuss.
Mountain (Hydrangea serrata)
A gentler cousin of the bigleaf with finer lacecap flowers and leaves, and a comforting extra hardiness in bud and stem that carries it through tough winters.
How to propagate
Hydrangeas are wonderfully easy to multiply at home, and you have two simple, beginner-friendly ways to grow a new one.
Stem cuttingsEasy
Late spring to summer · Several weeks to root
The simplest way to grow more hydrangeas, and a lovely first project, is a softwood stem cutting taken in late spring or summer. Give it warm, humid air and it will quietly root over several weeks into a young plant just like its parent.
LayeringEasy
Spring to summer · One season to root
Layering is even more foolproof if a low, bendy branch is within reach. Pin it gently to the soil in spring or summer, let it settle for a full season while roots form, then snip it free as its own little plant.
Myths
All hydrangeas can be trimmed alike, either in autumn or toward the end of winter.
There is no single pruning rule, and that is good news once you know the trick. Old-wood bloomers such as bigleaf, oakleaf, and mountain set buds right after flowering, so a cut from fall through early spring takes next year's flowers with it. New-wood bloomers like panicle and smooth are the ones you trim in late winter or early spring. Just find out which kind you have before you pick up the shears, and you are set.
Adjusting soil acidity will shift the blooms of any hydrangea from pink over to blue.
The color trick is a delight, but it only works on a couple of species. Only bigleaf and mountain hydrangeas answer to soil pH and aluminum, turning blue in acidic soil and pink in alkaline. White-flowered, panicle, and oakleaf types keep their color steady no matter what you try, so there is no need to fuss over them.