Overview
What hydrangeas need, when they flower, and whether they suit your garden.
When a hydrangea fails to flower, the usual cause is pruning at the wrong time, not a pest. Mophead and lacecap hydrangeas flower on buds made the summer before, so autumn and winter cuts remove this year’s flowers; panicle and smooth hydrangeas flower on new growth and can be cut hard in spring. Learn which you have, and they are very dependable.
Quick facts
- Botanical name
- Hydrangea macrophylla
- Hardiness
- USDA zone 6a and warmer
- Propagation
- Cutting, Division
Survives −23 °C
Growing details
- Frost sensitivity
- Frost hardy
Growing calendar
- Plant out: March, April, May, September, October
- Flowering: June, July, August, September
- Prune: March, April, July
- Propagate: May, June
Spring or autumn, when the soil is warm and moist. Bigleaf mid to late summer; panicle hydrangeas from late summer. Spring for most; bigleaf types can be trimmed as flowers fade, never after early August. Softwood cuttings from non-flowering shoots.
Is this plant right for you?
- Part shade
- Long flowering
- Good in pots
- Needs moist soil
- Colour changes with pH
- Pruning by type
- Toxic to pets
Toxic to pets
Toxic to dogs, cats and horses if eaten: vomiting, depression and diarrhoea (ASPCA).
Before You Grow
Identify or choose the type, then a spot with morning sun, afternoon shade and moist soil.
Hydrangeas are toxic to dogs, cats and horses if eaten (ASPCA).
What you need
The right hydrangea
Know its species: it decides pruning. See choose your hydrangea.
Morning sun, afternoon shade
Not a hot, dry, exposed site. See where they grow best.
Compost or leaf mould
To dig in and to mulch each spring. See soil.
A watering can or hose
Hydrangeas are thirsty. See watering.
Sharp secateurs
For deadheading and pruning. See pruning.
Sulfur or lime, optionally
To shift bigleaf flower colour. See soil.
Choose your hydrangea
Several species are grown, and they flower differently, so they are pruned differently.
Bigleaf hydrangea (H. macrophylla) is the familiar pink or blue shrub, with round mophead or flat lacecap flowers. Colour depends on soil pH. Most older varieties, such as ‘Nikko Blue’, flower only on last year’s stems; newer reblooming ones, such as Endless Summer and ‘Blushing Bride’, flower on old and new growth (Iowa State). Hardy in zones 6 to 9 (Penn State). Mountain hydrangea (H. serrata) is similar and smaller.
Panicle hydrangea (H. paniculata, ‘Grandiflora’ or PeeGee) grows 3 to 3.5 m (10 to 12 ft), with cone-shaped white flowers from late summer that age to pink, on new growth. It takes more sun (UMD).
Smooth hydrangea (H. arborescens, ‘Annabelle’) grows 1.2 to 1.5 m (4 to 5 ft) with round white heads on new growth.
Oakleaf hydrangea (H. quercifolia) has oak-shaped leaves, white summer flowers and fine autumn colour, on old wood; hardy to zone 5.
Climbing hydrangea (H. anomala subsp. petiolaris) clings to walls and tree trunks, even north-facing ones.
Hydrangea types compared
-
Bigleaf (mophead, lacecap)
- Flowers on
- Last year’s stems (rebloomers: both)
- Flowers
- Pink or blue by pH, or white
- When to prune
- Deadhead in spring; trim as flowers fade
-
Panicle (H. paniculata)
- Flowers on
- New growth
- Flowers
- White cones ageing pink
- When to prune
- Late winter or early spring, hard if you like
-
Smooth (H. arborescens)
- Flowers on
- New growth
- Flowers
- Round white heads
- When to prune
- Late winter or early spring, even to the ground
-
Oakleaf (H. quercifolia)
- Flowers on
- Last year’s stems
- Flowers
- White, ageing pink; autumn leaves
- When to prune
- Lightly, after flowering
-
Climbing (H. petiolaris)
- Flowers on
- Last year’s stems
- Flowers
- White lacecaps
- When to prune
- Only over-long shoots, after flowering
From Iowa State, Penn State, the RHS and Gardeners’ World. If flowers vanish after pruning or a cold winter, you probably have an old-wood type.
Where hydrangeas grow best
Most hydrangeas are woodland plants: they like light, moist shade.
Light. Morning sun and afternoon shade suit bigleaf hydrangeas best; avoid hot, dry, exposed sites (Clemson, UGA). Gardeners’ World advises against south-facing spots with dry soil. In full sun, UMD finds plants need more water, flower for less time and may scorch; too much shade means few flowers. Panicle hydrangeas take full sun to part shade.
Cold. Bigleaf hydrangeas survive zone 6 winters but can be killed to the ground, and a hard winter or late frost kills the flower buds (Penn State, UMD). Young spring growth is prone to frost damage.
Shade walls. For a shady wall, grow the climbing hydrangea.
- Light
- Morning sun, afternoon shade
- Bigleaf hardiness
- USDA zones 6 to 9
- Soil
- Moist, well-drained, rich
Soil and flower colour
Hydrangeas want moist, well-drained soil rich in organic matter. They grow in acid or alkaline soil, but pH changes the colour of pink and blue bigleaf and mountain hydrangeas.
Preparation. Dig plenty of compost or well-rotted manure into light soil before planting (Gardeners’ World); UGA works it into the top 20 to 30 cm (8 to 12 in) over a wide area.
Why colour changes. Aluminium in the flowers makes them blue. Acid soil, pH 5.0 to 5.5, makes aluminium available; as the pH rises it is locked up and flowers turn pink: from about 6.0 (Clemson) or 7.0 (UGA). In between you get purple, or both. White varieties don’t change.
For bluer flowers, lower the pH with sulfur, grow in ericaceous compost, and water with rainwater. UMD prefers sulfur or iron sulfate to aluminium sulfate, which can burn roots.
For pinker flowers, raise the pH with dolomitic lime. Test the soil first, and expect a year for the change to show.
Planting
Plant in spring or autumn, no deeper than the pot, into soil rich in organic matter.
Never plant deeper than the rootball sat in its pot.
When to plant hydrangeas
Spring or autumn, when the soil is warm and moist, is best (Gardeners’ World, Clemson). Summer planting works too, with extra watering until the roots establish.
Gift plants. Florists’ hydrangeas can be planted outside after flowering for repeat blooms each year (UGA).
- Spring or autumn is best.
- Summer planting needs extra water.
- Gift plants can go outside.
How to plant a hydrangea
A wide hole, the right depth and a good mulch.
-
Water the pot first
An hour or so before planting (Gardeners’ World).
-
Dig wide, not deep
Two to three times as wide as the rootball but no deeper (Clemson).
-
Set it level
The top of the rootball level with the soil surface. Never plant deeper than it grew in the pot.
-
Backfill and water
With the soil you dug out, then water thoroughly.
-
Mulch
With leaf mould, compost or bark, 5 to 7.5 cm (2 to 3 in) deep (Clemson), kept off the stems.
-
Wait to feed
Until the plant is established, four to eight weeks after planting (UGA).
Care
Plenty of water, light feeding, a spring mulch, and pruning matched to the type.
Bigleaf hydrangeas make next year’s flower buds in late summer. Don’t prune them after that.
Care through the year
Early spring
Mulch: leaf mould or compost
Deadhead bigleaf types and prune new-wood types. See pruning.
Spring
Feed: March and May
Protect new growth from late frost; feed lightly. See feeding.
Summer
Water: before plants wilt · Feed: July
Water in dry spells and heat. See watering.
Late summer
Prune: not after early August
Stop pruning bigleaf types: next year’s buds are forming.
Autumn and winter
Protect: cover in hard frost
Leave mophead flowerheads on to protect the buds below.
Watering hydrangeas
Hydrangeas are thirsty plants that like moist soil.
New plants. Water regularly, even weekly, through the first growing season (Gardeners’ World).
Established plants. Water deeply once a week, or more often in dry spells and heat (Clemson, UGA). Spring, when flowers are forming, is the time to avoid stress.
Midday wilting. Bigleaf hydrangeas can wilt on hot afternoons even in moist soil. If they recover overnight and the soil isn’t dry, it is heat, and they don’t need extra water (UMD).
Rainwater helps keep blue flowers blue.
Mulch every spring with leaf mould, compost or manure to hold moisture.
Feeding hydrangeas
Sources differ. Gardeners’ World usually doesn’t feed hydrangeas at all beyond a spring mulch, because feeding encourages leaves at the expense of flowers. US extensions give bigleaf hydrangeas several light feeds.
Light and balanced. UGA and Clemson apply a balanced fertiliser such as 10-10-10 at about 0.5 kg per 10 m² (1 lb per 100 sq ft) in March, May and July, watered in.
Not too much nitrogen. Excess nitrogen is one of the causes of a hydrangea not flowering (UGA).
For blue flowers, Gardeners’ World uses a fertiliser low in phosphorus and high in potassium.
Pruning hydrangeas
Pruning at the wrong time is the commonest reason hydrangeas don’t flower (UMD). It depends on the type.
Bigleaf (mophead and lacecap) and mountain hydrangeas flower on buds formed the previous late summer. Leave the old mophead flowers on over winter to protect the buds. In early to mid spring, cut each old flowerhead back to the first strong pair of buds (RHS). Also remove one or two of the oldest stems at the base to renew the plant. Iowa State waits until the shrub leafs out, then removes dead wood. Any trimming for shape is done as the flowers fade; UGA stops by 1 August.
Panicle and smooth hydrangeas flower on new growth. In late winter or early spring, cut last year’s stems back to a framework 30 to 60 cm (1 to 2 ft) high; Penn State cuts smooth hydrangeas to the ground. Harder pruning gives bigger heads (RHS).
Oakleaf hydrangeas flower on old wood: prune lightly, only dead and crossing stems.
Climbing hydrangeas need little: cut back over-long shoots after flowering.
Frost damage. Cut back to the first undamaged buds once growth starts.
Hydrangeas in containers
Bigleaf hydrangeas grow well in pots and make good patio plants; a pot can be moved into shelter on a cold night (UGA).
Compost. Peat-free ericaceous compost keeps flowers blue (Gardeners’ World).
Size. Choose a compact variety and a large pot with drainage holes, so the compost doesn’t dry out too fast. Watch for vine weevil in pots (Gardeners’ World).
Care. Pots dry quickly: water often in summer, with rainwater for blue flowers, and feed lightly.
Problems
No flowers, wilting and the wrong colour are the usual complaints; each has a clear cause.
Common hydrangea problems
Most hydrangea problems come from pruning, weather or site, not pests or disease (UMD).
No flowers
- Pruning
- Winter
- Shade
Pruned at the wrong time, flower buds killed by winter cold or a late frost, too much shade, too much nitrogen, or deer browsing (UGA, UMD, Penn State). See pruning.
Wilting on hot afternoons
- Heat
Normal for bigleaf types in sun. Water only if the soil is dry or plants don’t recover overnight.
Scorched leaves and flowers
- Too much sun
Too much sun for a woodland plant. Move it, or give afternoon shade and more water.
Blackened new shoots in spring
- Late frost
Frost damage. Cut back to healthy buds; cover plants with fleece or a sheet when frost is forecast.
Flowers only at the top
- No pruning
Unpruned panicle and smooth hydrangeas grow taller each year. Prune to a framework in spring.
More problems with hydrangea
Common pests
Hydrangeas have few pest problems (Penn State).
Deer
Browse buds and shoots, which costs old-wood types their flowers. Panicle hydrangeas are browsed less (Penn State).
Hydrangea scale
Brown scale insects on stems and under leaves, with white waxy egg masses in early summer; widespread in England since the 1980s (RHS).
More problems with hydrangea
Common diseases
Leaf spots
Brown or purple spots on leaves in wet weather (UGA). Usually cosmetic: remove unsightly leaves and water at the base (UMD).
Decline and dieback
Often soggy soil, drought or weather extremes rather than disease (UMD). Check drainage and watering first.
Harvest & Use
Cutting flowers for the house and drying them.
Cutting and drying flowers
Hydrangea flowers are attractive even as they fade, and they make good dried flowers (Penn State).
For drying, cut heads late in the season as they turn papery.
On bigleaf types, take flower stems with little extra stem, or wait until spring pruning, so you don’t remove the buds for next year.
- Cut fresh heads for the vase.
- Dry late-season heads.
- Don’t take next year’s buds.
Propagation
New plants from softwood cuttings, layering or division.
Propagating hydrangeas
Softwood cuttings. In late spring or early summer, take 7.5 to 12.5 cm (3 to 5 in) tips of non-flowering shoots with at least three leaves (UGA); Gardeners’ World asks for three sets of leaves. Cut just below a leaf joint, remove the lower two pairs of leaves, and halve the remaining leaves. Dip in rooting hormone and push into moist, gritty compost; keep humid and shaded until rooted.
Layering. Bend a low stem into a trench, remove a ring of bark where it touches the soil, and cover it, leaving 15 to 30 cm (6 to 12 in) of tip showing. It roots in place (UGA).
Division. Old, established clumps can be split with a spade in early spring (UGA).
More to Explore
Quick answers, related guides, and the sources behind this one.
Frequently asked questions
Why isn’t my hydrangea flowering?
Most often pruning at the wrong time; also winter damage, shade or too much nitrogen. See common problems.
When should I prune hydrangeas?
It depends on the type. See pruning.
How do I make my hydrangea blue?
Lower the soil pH to 5.0 to 5.5 with sulfur, or grow it in ericaceous compost and water with rainwater. White varieties won’t change.
How do I make my hydrangea pink?
Raise the pH to 6.0 or above with dolomitic lime. It can take a year to show.
Should I deadhead hydrangeas?
On mopheads, leave the old flowers over winter and remove them in spring, to the first strong buds.
Can hydrangeas grow in full sun?
Panicle types can. Bigleaf types prefer afternoon shade; in full sun they need more water and may scorch.
Why is my hydrangea wilting?
Often afternoon heat. If it recovers overnight and the soil is moist, it is fine.
Are hydrangeas poisonous to pets?
Yes: the ASPCA lists them as toxic to dogs, cats and horses.
Related guides
Sources
- Hydrangea pruning (opens in a new tab) Royal Horticultural Society
- Hydrangea (opens in a new tab) ASPCA Animal Poison Control
- Hydrangea care in South Carolina (opens in a new tab) Clemson Cooperative Extension
- Growing bigleaf hydrangea (opens in a new tab) University of Georgia Extension
- Hydrangea: identify and manage problems (opens in a new tab) University of Maryland Extension
- Pruning hydrangeas (opens in a new tab) Iowa State University Extension and Outreach
- When to prune which hydrangea species (opens in a new tab) Penn State Extension
- How to grow and care for hydrangeas (opens in a new tab) BBC Gardeners’ World