Shrub · Hydrangeaceae
Hydrangea
Hydrangea macrophylla
Give it rich, moist soil and afternoon shade, and the hydrangea answers with armfuls of bloom all summer.
Partial shade
Every 3–7 days
USDA 3–9
3–10 ft · 0.9–3 m
Overview
Hydrangeas are the big, romantic shrubs of the summer garden, smothered in rounded mophead heads, flat lacecaps, or tall cones depending on the type. The most famous of them, the bigleaf hydrangea, is the one that turns blue in acidic soil and pink in alkaline, a quirk that has fascinated gardeners for generations. They grow fast and bloom hard, reaching anywhere from 3 to 10 feet (90 cm to 3 m) across the different species.
The catch is that not all hydrangeas behave alike. Some bloom on old wood, setting their buds the summer before, while others bloom on new wood grown that same season. That single difference decides when you prune, whether a hard winter costs you flowers, and which types thrive where late frosts are common. Pick the right species for your zone and half the work is already done.
Beyond color and pruning, hydrangeas ask for little drama. They want steady moisture, shelter from the harshest afternoon sun, and soil rich in organic matter. Meet those and the plant rewards you for years, since it is a long-lived perennial shrub that only grows fuller with age.
Care
The short version: plant in rich, moist, well-drained soil with morning sun and afternoon shade, water deeply about once a week, and prune to match whether your type blooms on old or new wood.
Light
Hydrangeas do best in partial shade, ideally morning sun with shade through the hot afternoon. Bigleaf types in particular scorch and wilt in full afternoon sun, while panicle types take far more of it. Deep shade, though, cuts your flowers down sharply.
Water
Keep the soil evenly moist, watering deeply about once a week and more often in heat or in a pot. The name itself hints at the thirst, and bigleaf types are the first to flop when they go dry. A layer of mulch holds that moisture and keeps the roots cool.
Soil
Plant in rich, moist, well-drained soil loaded with organic matter. A pH of 5.0 to 6.5 suits them, on the acidic side, and for bigleaf and mountain types that acidity also steers the flowers toward blue.
Temperature
These are tough shrubs, hardy from about -20°F to 95°F (-29°C to 35°C) across the hardier species. A late spring frost is the real danger, since it can kill the formed buds on old-wood types and cost you a season of bloom.
Humidity
Ordinary outdoor humidity suits hydrangeas fine, so there's no target to hit. Air movement matters more than the number, because crowded, still, humid air invites leaf spot and powdery mildew.
Feeding
A balanced 10-10-10 fertilizer applied a few times from spring through mid summer is plenty. Go easy, since too much nitrogen pushes lush leaves and holds back the flowers you actually want.
Pruning
Time the cuts to the bloom wood. Prune old-wood bloomers like bigleaf, oakleaf, and mountain right after they flower and no later than August 1, and prune new-wood bloomers like panicle and smooth in late winter or early spring before growth starts.
Repotting
Hydrangeas are rarely repotted, since most live in the ground for good. If you grow one in a container, move it up a size when roots circle the pot, grow from the drainage holes, or water runs straight through without soaking in.
Size & spacing
Depending on the species, hydrangeas reach 3 to 10 feet (90 cm to 3 m) tall and spread 3 to 6 feet (90 to 180 cm) wide. Give each shrub room to fill out so air moves freely through the branches and disease stays at bay.
When to plant
Hydrangeas are hardy across zones 3 to 9, so the main timing question is when to plant and when to prune. Set new shrubs out in spring or fall while the weather is mild, expect bloom from late spring through summer, and let the bloom-wood type tell you when 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
Most hydrangea complaints come down to a few familiar issues: a plant that wilts in the heat, one that grows leaves but no flowers, or foliage marked by spots or yellowing. Match what you see below to its likely cause, then act before it sets the plant back.
Leaves and blooms drooping in the afternoon heat
When a hydrangea flops in the afternoon, it is almost always thirst and sun stress working together. Bigleaf types in particular wilt fast under hot direct sun, then perk up again in the cool of evening once the soil holds water. Move them to a spot with morning sun and afternoon shade, water deeply, and mulch the root zone to keep things even.
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
The usual culprit is pruning at the wrong time. Old-wood bloomers set next year's buds soon after they finish flowering, so a fall or spring trim cuts those buds clean off. A hard winter or a late frost can also kill the buds, and too much shade or heavy nitrogen pushes leaves at the expense of flowers. Learn whether your plant blooms on old or new wood, then time the shears to match.
Fix:
- Prune old-wood bloomers only right after flowering
- Protect old-wood types from late frosts
- Reduce shade and avoid heavy nitrogen feeding
Spotted leaves or a dusty white film on the foliage
Two fungal problems show up here. Cercospora and other leaf spots leave purple-rimmed marks with tan centers, while powdery mildew coats the leaves in a white film when plants are crowded and air sits still. Neither kills a healthy shrub, but both spread in damp conditions. Clear away marked and fallen leaves, water at the base to keep foliage dry, and open the plant up so air can move through it.
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
Pale yellow leaves with veins that stay green
Yellow leaves laced with green veins point to iron chlorosis, usually because the soil runs too alkaline for the plant to take up iron. It hits the newest leaves first. Test the soil and nudge the pH toward the slightly acidic range hydrangeas prefer, add organic matter to improve drainage, and apply iron only once a deficiency is confirmed.
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 toxic, and that includes the parts people find most tempting to handle. The leaves, buds, and flowers all contain cyanogenic glycosides, which can poison cats, dogs, horses, and grazing animals, and nothing on the plant is safe to eat. Keep clippings and fallen blooms away from pets and out of paddocks, and wash up after pruning.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Mild
A cat that nibbles the leaves or flowers usually ends up with vomiting and diarrhea, often followed by a stretch of low, listless energy. The bitter taste tends to stop them before they eat enough to do real harm.
Dogs Mild
Dogs are the most likely to chew on a shrub, and the result is an upset stomach, loose stools, and a noticeably flat, depressed mood. Watch a determined chewer closely, since a large mouthful raises the small risk of cyanide trouble.
Horses Mild
A grazing horse that gets into hydrangea can develop colic-like stomach upset, diarrhea, and dullness. Keep clippings and prunings well out of reach of paddocks.
Rabbits Toxic
The same cyanogenic glycosides make every part off-limits for rabbits, whose small size leaves little margin. Expect digestive distress and weakness, and keep the plant and its trimmings out of their space entirely.
Livestock Toxic
Cattle, goats, and sheep can browse hydrangea foliage and take in enough cyanogenic compound to cause real harm. Drooling, diarrhea, and laboured breathing are warning signs that call for a vet.
Birds Caution
The leaves and buds carry the same toxin that affects mammals, so pet and backyard birds should not pick at them. Treat any pecking at the plant as a reason to step in.
People Caution
No part of a hydrangea is meant to be eaten, and the leaves, buds, and flowers can cause stomach upset if swallowed. Keep curious children away from the blooms and wash up 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
Several hydrangea species share the name but differ sharply in flower shape, hardiness, and when they bloom. These are the main ones worth telling apart.
Bigleaf (Hydrangea macrophylla)
The familiar mophead and lacecap shrub whose flowers turn blue in acidic soil and pink in alkaline soil, blooming mostly on old wood except for reblooming Endless Summer types that flower on both old and new growth.
Oakleaf (Hydrangea quercifolia)
A native shrub with bold oak-shaped leaves and white cone-shaped panicles that age to pink, finishing the year with rich bronze fall color and blooming on old wood.
Panicle 'Limelight' (Hydrangea paniculata)
The toughest of the group, taking full sun and hard cold while carrying white-to-pink cone-shaped panicles on new wood, so you prune it in late winter.
Smooth 'Annabelle' (Hydrangea arborescens)
A native that throws huge white globe-shaped flower heads on new wood, which makes it forgiving to prune and reliable to rebloom.
Mountain (Hydrangea serrata)
A daintier cousin of the bigleaf with finer lacecap flowers and leaves, prized for being more cold-hardy and bud-hardy in tough winters.
How to propagate
Hydrangeas are easy to multiply at home, and you have two simple, beginner-friendly routes to a new plant.
Stem cuttingsEasy
Late spring to summer · Several weeks to root
The easiest way to make more hydrangeas is from softwood stem cuttings taken in late spring or summer. Keep them under high humidity and they root over several weeks into plants identical to the parent.
LayeringEasy
Spring to summer · One season to root
Layering is even simpler if you have a low, bendable branch. Pin it down to the soil in spring or summer, leave it for a full season to root, then cut it free as its own plant.
Myths
Every hydrangea should be pruned the same way, in fall or late winter.
Pruning has to follow the bloom-wood type. Old-wood bloomers like bigleaf, oakleaf, and mountain set their buds right after flowering, so cutting them from fall through early spring strips off next year's flowers. New-wood bloomers like panicle and smooth are pruned in late winter or early spring. Know which kind you have before you pick up the shears.
Any hydrangea can be turned from pink to blue by changing the soil pH.
The color trick only works on a couple of species. Only bigleaf and mountain hydrangeas shift color with soil pH and aluminum, going blue in acidic soil and pink in alkaline. White-flowered, panicle, and oakleaf types hold their color no matter what you do to the soil.