How to grow shrubby hydrangeas

Choosing a hydrangea

There are a number of different hydrangea types but they all enjoy similar growing conditions. They vary in size from small shrubs to sizeable, almost tree-like specimens so check the plant label when buying to get one that is suitable for your space.

Which hydrangea you choose will likely depend on your preferences for flower colour and/or shape.

Mophead and lacecap cultivars of Hydrangea macrophylla (and also Hydrangea involucrata and Hydrangea serrata) change colour depending on the acidity or alkalinity of the soil (pH) that affects aluminium availability.  Those with blue or pink flowers tend to be blue in acid soils (high available aluminium levels), mauve in lightly acid to neutral soil conditions, and pink in alkaline conditions. White, red and green-flowered cultivars, remain white or green regardless of soil pH.

Different hydrangea species also have differently shaped flowers. For round flower heads, choose mophead cultivars of Hydrangea microphylla (hortensia) or Hydrangea arborescens. For flatter flowers select lacecap cultivars of Hydrangea microphylla, Hydrangea serrata, Hydrangea villosa or Hydrangea aspera. And, finally, for cone-shaped flowers go for Hydrangea paniculata or Hydrangea quercifolia.

Buying a shrubby hydrangea

The best choice of hydrangeas in garden centres is available from mid-summer when they are in flower, but containerised plants are available all year round.

Check the height on the label as some will grow into sizeable shrubs.
In garden centres they are usually sold in 3 litre pots at 30cm or more in height. Mail order plants may be sold as young cuttings in 9cm or 1 litre pots. 

When to plant

Plant your shrubby hydrangea soon after purchase. The best time to plant is in spring or autumn. Containerised plants can be planted all year round as long as the soil is not frozen, too wet, or excessively dry in summer (but you can water them well if you really want to plant them then).

Soil preparation

Cultivars with blue flowers remain blue if they are growing in acidic soil (pH 4.5-5). For more information on soil acidity see our guides on this and on how to acidify your soil.

Where the blue colouring proves unreliable (you are getting purple and pink shades), you can use ‘hydrangea blueing compounds’, which contain aluminium sulphate. Always follow the manufacturer’s instructions. If the soil is very alkaline, or if there are obvious pieces of chalk in the soil, this treatment will not work and planting in containers with ericaceous compost is the best option. 

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.

Hydrangeas thrive in evenly moist soil so improve the planting area (not just the planting hole) by digging in organic soil improver, such as garden compost or a manure-based soil conditioner. Add a bucketful per square metre (yard) for the best results.

How to plant

• ​Water the plant well before planting
• Make your planting hole as deep as the rootball and three times wider
• Plant your hydrangea so that the surface of the compost in the pot is level with the surrounding soil to avoid planting too deep
• Firm the soil around the rootball well by pressing with the heal of your boot/shoe
• Mulch with a soil improver leaving, 10-15cm (4-6in) gap around the base, to reduce the drying out of the soil
• Water in to help establishment and aim to keep the soil damp in the coming weeks

Where to plant

• Ideally, plant your shrubby hydrangea in light shade. However, you can plant in a sunnier spot if the soil is not too dry in summer
• Plant away from frost pockets or exposed spots to reduce late frost damage to the new spring growth
• Spacing will depend on the vigour of the chosen plants, ranging  90cm-2.4m (3-8ft). Check the plant label for eventual size

Hydrangeas in containers

• Grown more compact hydrangea cultivars, such as Hydrangea macrophylla ‘Red Hot Violet’ and ‘Altona’, in containers
• If you are gardening on alkaline soils and want to retain blue flowers, grow your hydrangeas in containers using ericaceous compost
• Otherwise use a mix of two parts of John Innes No.3 and one-part peat-free multipurpose compost

Watering

• Water newly planted hydrangeas regularly during the first growing season from spring to summer when we’ve had no significant rain for 7-10 days
• Even mature plants will benefit from watering during hot dry spells. To reduce moisture stress, regularly mulch with organic matter, such as leafmould, garden compost or a manure-based soil conditioner, to help the soil retain moisture

• Check the moisture levels of containerised plants regularly and ensure they don’t dry out. Move containers to shadier spot in summer to reduce drying out 
• Water blue-flowered cultivars preferably with rainwater to retain the flower colour but, if rainwater is in short supply, use tap water to prevent drought stress

Feeding

Apply general fertiliser such as Vitax Q4, seaweed feed or fish, blood and bone after planting.

Regular feeding of established plants is not generally needed. Too much fertiliser encourages excessive soft, leafy growth, with plants less likely to develop flower buds and more at risk from frost damage.

Struggling shrubs growing on lighter, sandier soils may benefit of spring application of general fertiliser. Drought stress can also cause this problem so mulching may be more helpful.

Overwintering

Most hydrangeas are hardy throughout most of the UK, but the young buds may be susceptible to damage from late frosts. There is the option to move plants in containers to a more sheltered spot such as a cold greenhouse or against a sheltered, sunny wall to provide protection for the buds and new growth.

There is no need to wrap the pot, as this does not provide sufficient insulation to prevent the rootball freezing in an average winter.

You can place the pot on pot feet or a few bricks to improve drainage and so prevent waterlogging. In dry spells in winter, check that the compost does not dry out.

Deadheading mophead and lacecap hydrangeas (Hydrangea macrophylla)

• There is no need to immediately remove the faded flowers. The dead blooms can offer interest well into the winter and help protect the new tender growth below from frost damage

• Wait until mid-spring before cutting back the stems to the first or second strong healthy pair of buds down from the faded bloom

• If desired you can deadhead  lacecaps after flowering, but mopheads should be deadheaded in milder areas only

Pruning established mopheads and lacecaps (Hydrangea macrophylla), and H. serrata

• Prune in mid-spring

• Prune lightly, but regularly. The flowers are formed on new shoots growing from the previous year’s stems, therefore heavy pruning will result in loss of flowers

• Cut out one or two of the oldest stems at the base to encourage growth of new, more floriferous replacement shoots

• Renovate overgrown or neglected shrubs by cutting off all the stems at the base.  The new stems will not bloom until the following year

Pruning Hydrangea paniculata and H. arborescens 

• Prune in early spring, before the shrubs start actively growing

• Regular pruning is not essential, but annual pruning of last year’s growth encourages more prolific and larger flowers

• Prune last year’s growth to the lowest pair of healthy buds, creating a low framework of woody branches. This usually results in a pruned framework of no more than 25cm (10in) high but, if more height is required, cut to about 60cm (2ft) tall

• Neglected plants generally respond well to harder pruning to restore the low framework

Pruning other hydrangea species

These include Hydrangea aspera, H. aspera Villosa Group, H. quercifolia and H. sargentiana

• Prune in spring

• Only minimal pruning is needed to remove dead and over-long stems

They are easily propagated from cuttings. The plants will take two to three years to start flowering.

Take softwood cuttings from late spring to mid-summer, semi-ripe cuttings in mid-summer and or hardwood cuttings in winter.

Species hydrangeas can also be propagated from seed in spring.

Frost damage

New spring shoots are prone to frost damage. Prune back badly damaged shoots to just above the first undamaged pair of buds on live, healthy wood.

Hydrangea scale

Most noticeable in early summer when stems and leaves are covered with white, waxy, flat ‘blobs’.