Hydrangea

Hydrangeas are popular garden shrubs with delicate heads of flowers in shades of pink, white or blue and pretty autumn colour and leaf shape. The mophead and lace-cap hydrangeas are most well-known for their ability to change colour in different soils.

Hydrangea floribunda  'Paniculata'

Quick facts

Common name Hydrangea
Botanical Name Hydrangea
Group Shrubs and climbers, some evergreen
Flowering time late spring to late autumn
Planting time Autumn and spring
Height and spread Shrubs: 80cm-7m (32in–22ft) by 90cm–2.5m (3–8ft); climbers: up to 15m (50ft) high
Aspect Sun or partial shade
Hardiness H5 (hardy, cold winter) to H4 (hardy, average winter)
Difficulty Easy to moderate

Cultivation notes

Hydrangeas thrive in a moist, but well-drained soil, in a cool, semi-shady part of the garden. Try to avoid exposed east-facing sites, where cold winds may damage young spring growth, and also avoid dry, sunny spots.

Work plenty of organic matter into the soil prior to planting, and after planting and in subsequent years apply organic matter as mulch. This could be well-rotted leafmould, garden compost, composted bark, or farmyard manure.

Hydrangeas can be fed annually if necessary with fertiliser in late winter or spring.  This should be enough for the season, but should not be necessary on richer soils. On lighter, sandier soils, feeding is more likely to be helpful. Too much feeding can encourage excessive soft, leafy growth, with plants less likely to develop flower buds and more at risk from frost damage in colder winters.

Pruning and training

Climbing hydrangeas

Hydrangea anomala subsp. petiolaris, and H. seemanii are pruned after flowering, simply by removing spent flower heads and trimming any wayward shoots back to healthy buds.

Shrubby hydrangeas

See the advice page on pruning shrubby hydrangeas (such as H. macrophylla, H. paniculata and H. quercifolia). Most of these are pruned in early spring.

Flower colour

One of the most interesting quirks of some hydrangeas is the ability of the flowers to change colour. This is not true of all hydrangeas, but most often seen in the mophead and lacecap cultivars of Hydrangea macrophylla. Colour changes can also be seen in flowers of others such as H. involucrata and H. serrata

This colour change is due to the soil pH which affects aluminium availability. Those with blue or pink flowers tend to be blue in acid soil conditions (high available aluminium levels), mauve in acid to neutral soil conditions, and pink in alkaline conditions. To get the best flower colour, choose cultivars that give the best colours for the pH in question.

White flowers, and also green-flowered cultivars, remain white or green regardless of soil pH.

Try to use rainwater to water hydrangeas, since mains hard water can affect the flower colour, turning blue flowers mauve or pink.

Cultivars with blue flowers can be kept blue by growing the plants in acidic soil (pH 4.5-5), or by acidifying soils.  Where keeping hydrangeas reliably blue has failed, try using 'hydrangea blueing compounds' according to the manufacturer’s instructions. These compounds contain aluminium sulphate and are available from most garden centres. If the soil is very alkaline, or if there is any obvious chalk in the soil, this treatment will not work, but can be very effective for container-grown plants.

If you wish to enhance red or pink flowers, apply a dressing of ground limestone or chalk at a rate of 75-100g per sq m (2-3oz sq yd) in winter.

Propagation

Hydrangeas are easy to grow from softwood, semi-ripe or hardwood cuttings, but the climbing types are best layered.  Large clumps of Hydrangea macrophylla cultivars often lend themselves to division or layering.

Species hydrangeas can also be propagated from seed in spring.

Cultivar selection

A popular shrub, hydrangeas come in a number of habits and colours, from mophead, lacecap and paniculata types, to oak-leaved and climbing forms. A few are mentioned below but for a fuller list, see the RHS Plant Selector.

  • H. arborescens 'Annabelle' AGM: Deservedly popular cultivar with profuse spherical flowers to 30cm across opening greenish-white then aging to bright pure-white, from July to September. Height 1.2-1.5m (4-5ft).
    The recent introduction. H. arborescens Invincibelle Spirit='Ncha1' has pink flowers
  • H. aspera 'Macrophylla' AGM: Has huge domed flowerheads of blue-mauve flowers, surrounded by a ring of pure white sterile florets in either acid or alkaline soils during summer and autumn. Large downy leaves have good autumn tints. Height 3m (9ft)
  • H. aspera 'Peter Chappell' AGM: A compact cultivar with unusually, white flattened flowerheads ringed with white sterile flowers.  Height 2m (6ft)
  • H. involucrata 'Viridescens' AGM: A spreading dwarf shrub with bristly dark green leaves. Domed flowerheads in August are lilac surrounded by greenish ray florets. Height 1m (3ft)
  • Hydrangea macrophylla: Cultivars of these mophead and lacecap types are invaluable for poor soils, exposed positions and by the sea. Some interesting cultivars:
  • H. macrophylla 'Ayesha': Hortensia or mophead hydrangea with distinctive, large, dense, flattened lilac-like flowerheads composed of lightly scented thick cup-shaped petals, pale lilac-blue on acid soil or pale-pink on alkaline soils.  Height 1.5m (5ft)
  • H. macrophylla 'Love You Kiss' (Hovaria Series) AGM: a Japanese lacecap introduction. Reddish new leaves become rich green and distinctive large white flowers edged crimson-pink, are borne over a long period July to October. Height 1.5m (5ft)
  • H. macrophylla 'Merveille Sanguine': A mophead hydrangea with deep green leaves, flushed purple-red, deepening in colour as it ages. Flowerheads of deep-violet or crimson age to plum-purple. Height 1.2-1.5m (4-5ft)
  • H. macrophylla 'Zorro' AGM: Bushy upright lacecap hydrangea with dark purple-black stems. Toothed dark green leaves and masses of long-flowering large dark blue-purple flowers on acid soil or rich pink on alkaline soil through summer. Height 1.2-1.5m (4-5ft)
  • H. 'Preziosa' AGM: A compact and rounded mophead hydrangea with mauve-red stems. Leaves, purple-tinged when young, have good autumn tints. Globular flowerheads of rose-pink age to crimson-red, even on acid soils. Height 1-1.2m (3-4ft)
  • H. paniculata 'Big Ben' AGM: Very free flowering large conical flowerheads above red stems open pale green and gradually mature through white and pale pink to deep pink from August to October, height 1.7m (5.2ft)
  • H. paniculata 'Floribunda': Pointed flower panicles are creamy, developing some pink as they age. Flowers from late July to early September, height 1.9m (6ft) but can be kept smaller with regular pruning
  • H. paniculata 'Limelight' AGM: Very dense flowerheads are white, flushed lime-green and then pink as the season progresses. Flowering from July to October, height 1.65m (5.5ft)
  • H. paniculata 'Phantom' AGM: Slightly rounded, dense, conical flowerheads held on strong upright stems. Starting creamy-white, the huge panicles are flushed green and soft-pink and then deep-pink as the season progresses. Flowering July to September, height 1.45m (4.8ft)
  • H. paniculata Pinky-Winky='Dvppinky' AGM: A compact cultivar, one of the best for small gardens. Sturdy, upright reddish stems and dense conical flower panicles opening greenish-white, then pure white and maturing to deepest pink; often with all the colours in one spike. Flowering August to October, height 1.4m (4.8ft)
  • H. paniculata 'Silver Dollar' AGM: Has a compact habit and very dense broadly conical white flowerheads maturing to pink supported on strong stems. Flowering July to September, height 1.25m (4ft) is ideal for small gardens
  • H. paniculata Vanille Fraise='Renhy': Fluffy, loose, pyramid-shaped flower panicles are creamy-white, turning shades of pink as they age, before finally taking on rich pink tones. Flowering July to October, height 1.25m (4ft)  
  • H. quercifolia 'Pee Wee': Compact cultivar of the oak-leaved hydrangea. Lobed deep-green leaves turn bronze-purple in the autumn. Pure white upright flower panicles in summer become pink tinged into autumn. Height 1m (3ft)
  • H. quercifolia Little Honey='Brihon': A sport of H. quercifolia 'Pee Wee' with bright golden foliage. Height 1m (3ft)
  • H. quercifolia Snowflake-'Brido' AGM: Oak-leaved hydrangea with large mid-green leaves, bronze-purple in autumn and arching panicles of double-white flowers, later shading to pink, from July to autumn. Height 1.5m (5ft)
  • H. serrata 'Bluebird' AGM: Flattened flowerheads with bright-blue fertile flowers surrounded by large ray-florets or reddish-purple flowers, depending on the soil, from early July until well into the autumn and excellent autumn foliage colour. Height 1.2m (4ft)
  • H. serrata 'Grayswood' AGM: Flattened flowerheads of blue or mauve fertile flowers, surrounded by a ring of ray-florets, white at first changing to rose and finally deep-crimson and good autumn foliage colour. Height 1.2m (4ft)
  • H. serrata 'Tiara' AGM: Profuse sterile flowers open blue and turn mauve-pink over a long period from July to autumn and rich autumn foliage colour. Height 1-1.2m (3-4ft)

Links

AGM Plants
RHS Plant Finder

    Hydrangea arborescens 'Annabelle'Hydrangea paniculata 'Floribunda'Hydrangea serrata 'Graciosa'Hydrangea serrata 'Miyamayae-murasaki'Hydrangea macrophylla 'Love You Kiss' (Hovaria Series)Hydrangea quercifoliaHydrangea paniculata [Vanille Fraise] = 'Renhy'Hydrangea aspera 'Macrophylla'

    Problems

    Hydrangeas are usually robust shrubs. Non-flowering can be caused by frost damage to flowering wood, over-zealous pruning, pruning at the wrong time, or over-feeding with fertiliser too high in nitrogen.

    Hydrangeas may occasionally be affected by pests such as scale insects, hydrangea scale, capsid bugs, aphids and vine weevil.

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    • Kazzie avatar

      By Kazzie on 13/07/2014

      I've inherited three lovely Hydrangea bushes when I moved to this house. However, I have noticed that all three have holly plants growing through them. They are in different parts of the garden, not together. Is this just coincidence or is there are reason the previous owner did this?

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    • juliasavory avatar

      By juliasavory on 23/07/2014

      I've realised that I could have planted my new hydrangeas in too dry an area in my garden. They were new plants this spring. Can I move them? When should I do this? Also the edges of the petals are turning brown/yellow? Is there a reason for this? Thanks for any help.

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