Shrub
How to grow hydrangeas
Hydrangea macrophylla (mophead/lacecap), H. paniculata, H. arborescens
Plant hydrangeas in moist, well-drained soil in light shade or morning sun, out of cold east winds that scorch spring growth. Find out which type you have before you prune: mopheads and lacecaps flower on last year's wood and want only a light tidy in spring, while paniculata and Annabelle types flower on new wood and are cut hard. Flower colour in mopheads follows soil pH, blue on acid soil and pink on alkaline.
- Hardiness
- Fully hardy (new growth frost-prone)
- Position
- Part shade to sun, sheltered
- Soil
- Rich, moisture-retentive, free-draining
- Ideal pH
- 5.5 to 7.0
- Water
- High, wilts fast in dry spells; mulch
- Feeding
- Moderate feeder
Sowing and planting hydrangeas
WhenPlant Mar to Apr or Sep to Oct; flowers Jul to Oct; prune Mar by type
Starting off
Plant pot-grown stock Mar to Apr or Sep to Oct into soil enriched with garden compost. Propagate by 10 to 15 cm softwood cuttings in Jun to Jul under a plastic bag (root in 3 to 4 weeks at 18 to 21°C) or hardwood cuttings 20 cm long in Nov.
Spacing and planting
Final spread 1.5 to 2 m for mopheads, 2 to 2.5 m for H. paniculata; plant 1.5 m apart in a hole twice the rootball width with the top of the rootball level with the soil. Mopheads do well in a 40 to 50 cm pot of ericaceous compost if watered daily in summer.
Varieties worth growing
- H. macrophylla 'Endless Summer'
- Mophead that flowers on old and new wood, so a late frost or hard prune does not cost the whole year.
- H. macrophylla 'Blue Wave' (Mariesii Perfecta)
- Lacecap, hardier and more elegant than most mopheads; blue on acid soil, pink on alkaline.
- H. paniculata 'Limelight'
- Cone flowers from lime-green to pink, flowers on new wood, pruned hard in March, any soil, full sun.
- H. arborescens 'Annabelle'
- Huge white heads on new wood; takes shade and clay, pruned to 30 cm each spring.
- H. serrata 'Bluebird'
- Compact lacecap to 1.2 m for a pot or small bed; hardy and reliably blue in ericaceous compost.
Hydrangeas month by month
Timings are for central England. Allow two weeks later in the north and on cold, heavy soil.
- January
Nothing. Old flower heads stay on.
- February
Order plants. Test soil pH if you want blue.
- March
Prune: mopheads to the first strong buds, paniculata and arborescens hard to 30 to 60 cm. First feed and mulch. Aluminium sulphate for blue.
- April
Plant. Second aluminium sulphate dose. Fleece on frosty nights.
- May
Water new plants weekly. Watch for capsid damage; ignore it.
- June
Second feed. Softwood cuttings under a bag. Start daily watering of pots.
- July
Flowering. Sulphate of potash if the plant is all leaf. Deep water in drought.
- August
Cut heads for drying as they turn papery. No more feeding.
- September
Plant in the second half of the month. Autumn colour on paniculata.
- October
Keep old heads on. Reduce watering.
- November
Hardwood cuttings 20 cm long in a cold frame.
- December
Rest. Check pots are not waterlogged.
Feeding hydrangeas
A moderate feeder that wants water more than food. Balanced in spring, potash in early summer, and nothing after July so the wood ripens before winter.
A balanced-to-potassium feed in spring; keep it well watered ('hydra' means water).
Feeding plan
March, beds
100 g/m² (a double handful per plant) round the drip line, then a 5 cm mulch of compost or composted bark.
March and June, pots
2 to 4 g per litre of compost on the surface: 60 to 100 g for a 45 cm pot each time.
June to July, every 2 to 4 weeks
Potassium Rich Fertiliser 11% K
0.5 to 1 g per litre of water as a drench; or, for a plant that is all leaf, Sulphate of Potash at 20 g/m² once in July.
Autumn before, for blue mopheads
To bring the pH under 5.5: 55 g/m² on sand, 110 g/m² on loam in two doses, 175 g/m² on clay in three; never more than 80 g/m² at once. Test first.
March and April, for blue mopheads
Aluminium sulphate
15 g per 10 litres of water round the roots, twice. Never lime a blue hydrangea.
Signs to watch
Yellow leaves with green veins on young growth → iron locked out by alkaline soil or hard mains water → rainwater, sulphur chips and an ericaceous feed containing chelated iron. Mopheads that fade from blue to muddy pink → aluminium unavailable as pH rises → aluminium sulphate at 15 g per 10 litres in Mar and Apr, never lime. Lush dark leaves but few or no flowers → excess nitrogen or buds frosted
Pests, diseases and problems
New shoots blackened and limp after a cold night in April or May
Late frost on soft growth
Leave old flower heads on until late March as insulation, plant out of frost pockets, fleece on forecast nights, and cut damaged shoots back to healthy buds in June.
Young leaves yellow between green veins
Iron lock-up on alkaline soil or from hard tap water, worst in pots
Rainwater, a sulphur acidifier, an acid mulch; repot pot plants in ericaceous compost.
Pot plants wilt and collapse, roots eaten
Vine weevil grubs
Nematodes watered in during late August and April.
Ragged holes and brown spots on young leaves, shoot tips distorted
Capsid bug feeding in May and June
Tolerate; it is cosmetic. Clear plant debris where the bugs overwinter.
Grey or white powder on leaves in late summer, leaves purple-tinged
Powdery mildew on a dry-rooted plant
Water deeply, mulch, improve air flow; remove worst leaves.
Brown or purple spots on leaves with yellow halos
Leaf spot fungi in a wet summer
Rake up fallen leaves, water at the base, feed to keep the plant vigorous.
Pruning
Pruning and care
Mopheads and lacecaps flower on last year's wood: in Mar cut spent heads back to the first strong pair of buds and remove 1 in 3 of the oldest stems at the base. H. paniculata and H. arborescens flower on new wood, so cut all stems back to 30 to 60 cm in Mar. Leave old flowerheads on through winter to protect the buds; renovate by cutting everything to 30 cm in Mar and forgoing one summer's flowers.
Good to knowOn acid soil (or with aluminium sulphate) mopheads are blue; on alkaline soil they're pink. Prune by type.
Growing hydrangeas in pots
Mopheads, lacecaps and H. serrata do well in a 40 to 50 cm pot; H. paniculata and 'Annabelle' get too big. Use ericaceous compost for blue, loam-based for pink, and the 4-4-4 through it. A hydrangea in a pot wilts by lunchtime on a hot day: water every morning from May to September, stand the pot in part shade, and mulch the surface. Top-dress with fresh compost every March and repot every three years. In a hard winter move the pot against a sheltered wall or into a cold greenhouse rather than wrapping it.
Hydrangeas: common questions
How do I make my hydrangea blue?
Only mopheads and lacecaps (H. macrophylla and H. serrata) change colour. They need a pH below 5.5 and aluminium in the soil: acidify with sulphur, water with rainwater, and apply aluminium sulphate at 15 g per 10 litres in March and April. In a pot, use ericaceous compost. White varieties stay white whatever you do.
Why does my hydrangea not flower?
Pruned at the wrong time or frosted. Mopheads flower on last year's wood, so cutting them back hard in spring removes the buds; only remove old heads and a third of the oldest stems. Leave heads on over winter to protect buds from frost. Excess nitrogen is the third cause.
When should I feed a hydrangea?
A balanced feed in March with a mulch, a lighter dose in June, potash through early summer if the plant is leafy, and nothing after July. Late feeding gives soft growth that frost kills.
Sources
Growing information on this page was checked against these references in November 2026. Feeding rates are Dr Forest label rates.