Types of hydrangeas: 6 species + pruning by type

Types of hydrangeas: 6 species + pruning by type

Hydrangeas frustrate more gardeners than any other shrub for one reason: getting the pruning wrong eliminates a year of bloom. The fix is simple — once you know which of the six species you own, you know which wood it blooms on, and that single fact tells you when to prune. This guide walks through the six hydrangea species sold in US and UK nurseries, with visual ID, bloom timing, and the old wood versus new wood pruning rule that determines whether your shrub flowers. Pet safety also matters because the ASPCA confirms all hydrangeas are toxic to dogs, cats, and horses — the cyanogenic glycoside amygdalin in leaves and flowers releases small amounts of cyanide when chewed.

Match a hydrangea to your bed: Photograph your border in Growli and we measure light hours, soil pH cues, and existing planting — then rank the hydrangea species most likely to thrive where you live.

How the 6 species are grouped — old wood vs new wood

The single most important distinction in hydrangea care is which wood the flower buds form on. This determines pruning timing, frost vulnerability, and whether your shrub will reliably bloom each year.

Old wood bloomers — buds form on last year's growth in late summer, sit on the stems through winter, and open the following spring or early summer. Pruning the wrong stems in autumn or early spring removes next year's flowers.

• Hydrangea macrophylla (bigleaf)
• H. quercifolia (oakleaf)
• H. serrata (mountain)

New wood bloomers — buds form on the current season's new growth in spring, so you can prune hard in late winter or early spring without losing flowers.

• H. paniculata (panicle)
• H. arborescens (smooth)

Old and new wood (reblooming) — most modern reblooming bigleaf hydrangeas — Endless Summer series, Let's Dance series, BloomStruck — flower on both old and new wood, so they recover from late frosts that kill the previous year's stems.

Climbing hydrangea is unique — it blooms on old wood but rarely needs pruning beyond shaping.

The 6 species of hydrangeas

1. Bigleaf hydrangea — Hydrangea macrophylla

The hydrangea most people picture. Includes both mophead types (large rounded ball-shaped flower heads) and lacecap types (flat clusters with a ring of large showy florets around a centre of small fertile florets). Native to coastal Japan. The species famous for changing colour with soil pH — acidic soil (pH below 6) gives blue flowers, alkaline soil (pH above 6.5) gives pink. White cultivars stay white regardless.

The most-planted cultivars are 'Nikko Blue' (mophead, deep blue in acid soil), 'Endless Summer' (the original reblooming mophead, flowers on both old and new wood), and 'Lanarth White' (lacecap, white).

Bloom time: Early to mid-summer (June to July). Height: 3 to 6 feet. Sun: Part shade — morning sun, afternoon shade in zones 6+. Zones: USDA 5 to 9. Pruning: OLD WOOD — prune immediately after flowering in late summer. Never prune in autumn or spring. Cut spent flower heads back to the first strong pair of buds below the bloom.

2. Panicle hydrangea — Hydrangea paniculata

The cone-shaped white-flowering hydrangea that opens in mid to late summer. Cold-hardy, sun-tolerant, and the easiest hydrangea to grow in the US Midwest and across the UK. Flower panicles often shift from white to pink or rose as they age into autumn, then dry to tan for winter interest.

The most-planted cultivars are 'Limelight' (large lime-green panicles fading to white), 'Pinky Winky' (white aging to deep pink), 'Quick Fire' (early bloomer, white to red), 'Bobo' (dwarf, 3 feet tall), and 'Vanilla Strawberry' (cream aging to strawberry red).

Bloom time: Mid to late summer (July to September). Height: 3 to 12 feet depending on cultivar. Sun: Full sun to part shade — the most sun-tolerant hydrangea. Zones: USDA 3 to 8 — the most cold-hardy hydrangea. Pruning: NEW WOOD — prune in late winter (February to early March) before new growth starts. Cut back by one-third to one-half of the previous year's growth for larger flower panicles on more compact plants.

3. Smooth hydrangea — Hydrangea arborescens

Native to the US Southeast and Midwest. Soft rounded white flower heads on upright stems. The cultivar 'Annabelle' is the most-planted smooth hydrangea in the world — huge dinner-plate-sized white mopheads on 4-foot stems. Newer cultivars 'Incrediball' (larger, stronger stems that resist flopping) and 'Invincibelle Spirit II' (pink) extend the colour range.

Smooth hydrangea is the most forgiving species — sun-tolerant, cold-hardy to zone 3, and bulletproof for beginners. Stems can flop under wet flower heads — site near supportive companion plants or use a peony ring early in the season.

Bloom time: Early to mid-summer (June to August). Height: 3 to 5 feet. Sun: Part shade to full sun. Zones: USDA 3 to 9. Pruning: NEW WOOD — cut back hard to 12 to 18 inches above ground in late winter. The stronger the prune, the larger the flower heads.

4. Oakleaf hydrangea — Hydrangea quercifolia

Native to the US Southeast. Deep-lobed oak-shaped leaves that turn burgundy, purple, and crimson in autumn. White cone-shaped flower panicles in early to mid-summer that age to dusty rose. Exfoliating cinnamon-red bark adds winter interest. The only hydrangea with four-season ornamental value.

The most-planted cultivars are 'Snow Queen' (upright, white aging to pink), 'Alice' (large vigorous selection), 'Ruby Slippers' (compact, deeper pink ageing), and 'Pee Wee' (dwarf, 3 feet).

Bloom time: Early summer (June). Height: 4 to 8 feet. Sun: Part shade to part sun — afternoon shade in hot zones. Zones: USDA 5 to 9. Pruning: OLD WOOD — prune lightly immediately after flowering. Most oakleaf hydrangeas need minimal pruning — just remove dead wood and shape after bloom.

5. Mountain hydrangea — Hydrangea serrata

The smaller, cold-hardier cousin of bigleaf hydrangea. Mostly lacecap-flowered with delicate clusters of small flowers. Native to mountainous regions of Japan and Korea. More cold-hardy than H. macrophylla and less prone to losing flower buds to late frosts.

The most-planted cultivars are 'Bluebird' (deep blue lacecap), 'Preziosa' (mopheads aging from pink to red-purple), and 'Tuff Stuff' (reblooming lacecap, flowers on old and new wood).

Bloom time: Early to mid-summer (June to July). Height: 3 to 5 feet. Sun: Part shade. Zones: USDA 5 to 9. Pruning: OLD WOOD — prune immediately after flowering. Same rules as H. macrophylla.

6. Climbing hydrangea — Hydrangea anomala petiolaris

A true self-clinging woody climber that reaches 30 to 50 feet up walls, mature trees, and large fences. Holds itself in place with aerial rootlets like ivy or Boston ivy. Flat lacecap-style white flower clusters in early summer. Exceptional shade tolerance — one of the few flowering climbers that performs in deep shade. Slow to establish (often takes three years before significant growth or flowering) but long-lived.

Bloom time: Early summer (June). Height: 30 to 50 feet climbing. Sun: Part shade to full shade. Zones: USDA 4 to 8. Pruning: OLD WOOD — minimal pruning needed; trim shape only after flowering.

PET SAFETY — hydrangeas are toxic to dogs, cats, AND horses (ASPCA)

The ASPCA toxic plants database lists Hydrangea as toxic to dogs, cats, and horses. The toxic principle is the cyanogenic glycoside amygdalin, which is found in leaves, buds, and flowers. When chewed, plant tissue releases small amounts of hydrogen cyanide.

Clinical signs include vomiting, depression, diarrhea, and lethargy. The ASPCA notes that cyanide intoxication is rare in pet hydrangea ingestions and that symptoms are usually more gastrointestinal than systemic — but cats can be more affected than dogs because of their smaller body size, and toxicity is dose-dependent (more chewed leaves means more toxin).

A pet chewing a leaf or two will usually develop mild GI signs and recover within 24 hours. Chewing a large bouquet of cut flowers or stripping multiple leaves can produce more serious vomiting and depression. Cut hydrangea bouquets are still a risk — many indoor pet poisonings happen when cats chew arrangements brought in from the garden.

If a pet ingests any part of a hydrangea, call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435. Provide an estimate of how much was eaten and observe for vomiting, diarrhea, lethargy, or unusual breathing patterns.

How to choose the right type of hydrangea

Start with your climate. In USDA zones 3 to 4, only H. paniculata and H. arborescens are cold-hardy enough to bloom reliably — bigleaf and mountain hydrangea lose flower buds to late frosts. In zones 5 to 7, all six species perform. In zones 8 to 9, bigleaf and lacecap hydrangeas dominate.

Pick by light. Climbing hydrangea, oakleaf, and bigleaf prefer part shade. Smooth and panicle hydrangeas tolerate full sun in cool zones (zones 3 to 6). Avoid full afternoon sun on bigleaf hydrangeas in zone 7 and warmer — they wilt.

Pick by colour preference. Want blue or pink that you can shift with soil pH? Plant bigleaf or mountain hydrangea. Want classic white that ages to pink? Plant panicle or smooth hydrangea. Want autumn leaf colour and exfoliating bark? Plant oakleaf hydrangea.

Avoid the pruning trap. If you are unsure about your own pruning discipline, plant a new wood bloomer (H. paniculata or H. arborescens). These species flower reliably even after aggressive winter pruning, while bigleaf hydrangeas punish wrong-timing pruning with a flowerless year.

Pruning hydrangeas — the rule that confuses everyone

This is the most-confused topic in shrub gardening, so here is the simple version per RHS guidance:

H. macrophylla (bigleaf), H. serrata (mountain), H. quercifolia (oakleaf) — these bloom on OLD WOOD. Buds set in late summer for next year's flowers. Prune immediately after flowering (late summer / early autumn) by cutting spent flower heads back to the first strong pair of buds below the bloom. Never prune in autumn (after late September), winter, or early spring — you remove next year's flowers. Leave the brown winter heads on through winter for frost protection.

H. paniculata (panicle), H. arborescens (smooth) — these bloom on NEW WOOD. Flower buds form on the current year's growth. Prune in late winter (February to early March before bud-break) by cutting back one-third to one-half of the previous year's growth. Smooth hydrangeas tolerate even harder pruning down to 12 to 18 inches above ground.

Reblooming bigleaf cultivars (Endless Summer, BloomStruck, Let's Dance) bloom on both old and new wood. Light pruning only — remove only dead wood in spring and deadhead spent flowers.

Climbing hydrangea — minimal pruning. Trim to fit the space immediately after flowering.

Common care across the category

Water deeply once a week during summer. Hydrangeas have shallow root systems and wilt quickly in dry spells — deep weekly watering beats shallow daily sprinkles. Mulch 2 inches deep with shredded bark or compost to conserve moisture.

Feed in early spring with a balanced fertilizer or compost top-dressing. Avoid high-nitrogen fertilizers — they push leaf growth at the expense of flowers.

Adjust pH for colour on bigleaf and mountain hydrangeas. Add aluminium sulphate or pine bark mulch in spring to acidify soil for blue flowers. Add garden lime in autumn to raise pH for pink flowers. pH changes take 1 to 2 years to fully express. White cultivars do not change colour.

Protect old wood bloomers from late frost. In zones 5 to 6, a hard frost in late April can kill the flower buds on H. macrophylla even after the shrub itself survives. Cover with frost cloth or move container-grown bigleaf hydrangeas to a sheltered position during cold snaps.

Try Growli: Snap a photo of any hydrangea with Growli — instant ID, species confirmation, and pruning rule in 60 seconds.

Related articles

• Types of flowers — 20+ annuals and perennials — the broader category
• Types of peonies — tree, herbaceous, intersectional — another late-spring shrubby perennial
• Types of roses — 12 varieties for every garden style — the other classic flowering shrub
• Pet-safe houseplants — 20 non-toxic plants — indoor alternatives for pet households
• Types of soil — clay, sand, loam, silt — for picking hydrangea-friendly drainage
• Companion planting guide — what to plant under hydrangeas

Reviewed and updated by the Growli editorial team. For questions about anything here, open Growli and ask — or email hello@getgrowli.app.