In short
- Partially shaded site, acidic, humus-rich, and consistently moist soil.
- Flower color is controlled by pH: acidic = blue, alkaline = pink.
- Needs generous watering — tolerates drought poorly.
- Blooms on last year's wood — prune carefully in spring.
- All parts are mildly toxic to people and animals.
- The colorful "petals" are the sepals of the sterile flowers — the flower head keeps its look for weeks and dries well.
- White cultivars do not change color with pH — blue and pink apply only to the colored cultivars.
- Reblooming cultivars such as Endless Summer also set buds on the current year's shoots, so they usually flower even after frost damage — though later and less abundantly than after a mild winter.
Botanical data
- Family
- Hydrangeaceae (Hydrangeaceae)
- Height
- 1–2 m
- Width
- 1–2.5 m
- Habit
- Rounded
- Growth rate
- Moderate
- Position
- Partial shade, Shade
- Soil
- Humus-rich, Loamy
- pH reaction
- pH 4.5–6.5
- Moisture
- Moist
- Bloom
- June–September
- Hardiness
- USDA 6a–9b
- Propagation
- From cuttings, By layering
Characteristics
A compact, ball-shaped shrub with large, oval, toothed leaves. The flowers are gathered into showy mophead or lacecap clusters; their color depends strongly on the availability of aluminum, which is regulated by soil pH. Botanically the inflorescence is a compound cyme (a corymb-like cyme) — words such as "umbel" are used here only in the everyday, horticultural sense. It reaches 1–2 m in height and is often wider than it is tall (1–2.5 m), forming a dense, dome-shaped mass with no clear leader. It grows at a moderate rate but is long-lived — a well-managed shrub lasts several decades. The shoots are thick and sparsely branched, with conspicuous leaf scars. The leaves are opposite, thick and glossy, 10–20 cm long (hence the epithet macrophylla, meaning large-leaved) and sharply toothed; in autumn they usually drop without striking color. The inflorescence is made up of two kinds of flowers: small fertile ones in the center and large sterile ones around the edge. The latter provide the color, and their colorful "petals" are in fact sepals — which is why the flower head keeps its look for weeks and dries well, holding its color for a long time, though it gradually fades. In mophead cultivars almost all the flowers are sterile; in lacecap types they form only a ring around the fertile center. The shift to blue happens only below a pH of about 5.5, when aluminum becomes available to the roots; white cultivars do not respond to soil reaction at all. It blooms from June to September on shoots that grew the previous season. It grows best in partial shade; it also tolerates full shade, but flowers noticeably less there. It needs humus-rich, consistently moist soil with a pH of 4.5–6.5; on limestone soils and when watered with hard water it quickly develops iron chlorosis. It differs from panicle hydrangea (Hydrangea paniculata) in its thick, glossy leaves and its ball-shaped or flat-topped flower clusters instead of conical panicles.
Popular cultivars
- ‘Endless Summer’
- The original cultivar of the Endless Summer series (trade name for the cultivar Bailmer), reblooming: it sets buds both on last year's wood and on the current year's shoots, so it usually flowers even when the buds have been damaged by frost. Mophead flower clusters, a low shrub of about 1–1.5 m. Later cultivars in the same series (including BloomStruck, Twist-n-Shout, Blushing Bride) differ in habit and inflorescence type.
- ‘Nikko Blue’
- A classic mophead cultivar with large flower clusters — intensely blue on acidic soil with available aluminum, pink where the soil reaction is close to neutral. Vigorous, one of the most widely planted in open ground.
- ‘Blaumeise’
- A lacecap cultivar from the Swiss Teller series: a ring of large sterile flowers around a flat, fertile center, deep blue on acidic soil. A lacecap form, less bulky than the mopheads.
- ‘Mariesii Perfecta’
- Also known as Blue Wave — a lacecap with a light, delicate flower cluster and a color ranging from pink to blue depending on pH. Awarded the Royal Horticultural Society's AGM.
- ‘Madame Emile Mouillère’
- An old French cultivar from 1909 with white, ball-shaped flower clusters; the flowers turn pink with age. The white does not respond to soil reaction, though the eye at the center of the flower may be pink or blue. One of the taller mophead cultivars — it grows to about 2 m, the upper limit given for the species.
- ‘Ayesha’
- Recognizable by its unusual flowers: the sepals are cupped and concave, which makes the flower cluster resemble a flowering lilac. Flowers pink or lilac-blue, leaves exceptionally thick and glossy.
Growing and care
Watering
The large leaves transpire heavily — regular, generous watering is needed in hot weather. The name Hydrangea (Greek for "water vessel") says it all.
Fertilizing
Acidifying fertilizers enhance the blue flower color.
Planting
Fertile, humus-rich, acidic, and consistently moist soil; add peat or bark to acidify and mulch.
Pruning calendar
Pruning group: Hydrangeas flowering on old wood (garden, climbing)
What and how to cut
In early spring (after the frosts have passed), remove only the spent flower heads down to the first pair of healthy buds and cut out dead shoots; leave healthy shoots.
Early spring, after the last frosts.
What not to do
Do not shorten healthy shoots in spring or ‘shear’ the whole shrub — you will lose the flowering.
Companion plants
Good companions
Shares a preference for partial shade and moist, humus-rich soil — a good shade-loving combination.
Similar water and light requirements; the contrast in texture highlights the hydrangea's flower clusters.
An acid-loving plant with similar soil requirements — easy to grow and care for together.
Bad companions
Need dry, alkaline soil and full sun — the opposite of the hydrangea's requirements.
The evidence level indicates whether the relationship is backed by research, observation, or gardening tradition.
Diseases and pests
A white, powdery coating on leaves, shoots and buds. The leaves turn yellow, become deformed and drop prematurely. The coating develops on both sides of the leaf blade, is often clearly visible from above, and can easily be rubbed off with a finger — it is the superficial mycelium of an ectoparasite that draws nutrients from the epidermal cells by means of feeding structures (haustoria). At first single, round, white spots appear, which in time merge and cover the entire leaf surface and the young growth. Young leaves and the current season's shoots are the most susceptible; heavy infection causes them to pucker, stiffen and stop growing, and on buds it leads to deformation or death of the flowers. On the fruit of some species (gooseberry, apple, cucurbits) the coating leaves russeting or a corky skin. Towards the end of the season, small, dark fruiting bodies (chasmothecia, formerly called cleistothecia) — the pathogen's overwintering structures — appear within the coating. The disease affects many plants, including roses, oak, privet, lilac, cucurbits, cereals, grapevine, apple, gooseberry, phlox and coneflowers, with each of these hosts being infected by a specialised species of fungus.
Iron chlorosis (lime-induced chlorosis)The symptom affects acid-loving plants — hydrangea, rose, rhododendron, blueberry and others — grown on alkaline or calcareous soils. The leaf blade turns yellow while the veins remain distinctly green, producing the characteristic interveinal chlorosis. The symptoms appear first on the youngest leaves at the shoot tips, because iron is not very mobile within the plant and is not translocated into new growth. In extreme cases the leaves are almost white and their margins dry out. Crucially, the cause is usually not a lack of iron in the soil but too high a pH, which blocks its uptake by the roots. It is worth noting that not all susceptible plants are equally acid-loving — the rose prefers a slightly acidic to neutral reaction (about pH 6–7) and also develops iron chlorosis on strongly alkaline, calcareous soils, although it is not acid-loving in the way rhododendron or blueberry is. The pattern of yellowing is very regular: not only the main vein stays green but the whole fine network of veins, so that the leaf looks like green lace on a yellow-green background — this is the most reliable diagnostic feature, distinguishing interveinal chlorosis from the uniform, whole-surface yellowing typical of nitrogen deficiency. The symptoms intensify with each successive flush: older leaves at the base of the shoot may still be green or only slightly paled, and the younger the leaf, the paler it is, up to almost white, lemon-yellow tips. Under a long-lasting deficiency the margins and tips of the youngest leaves turn brown and necrotic, shoots grow more weakly and become smaller, and in blueberry the yield and fruit quality decline. Iron chlorosis is not contagious — it does not spread from plant to plant but appears simultaneously in all specimens growing on the same, overly alkaline site, which also helps to distinguish it from infectious diseases. Its severity can vary through the season: cold, wet and compacted soil, poor root aeration, excess calcium, a high bicarbonate content in the watering water, and over-fertilization with phosphorus additionally hinder iron uptake and aggravate the symptoms even when the element is not lacking in the soil.
Downy mildewYellow or angular (vein-bounded) spots on the upper leaf surface, matched underneath by a grey-violet or brown coating of spores. It differs from powdery mildew, whose white coating sits on the upper surface. It develops in humidity and cool nights and is dangerous to cucumbers, onions and grapevines. The spots are initially light green or yellowing, and their angular, mosaic-like shape arises because the pathogen's spread is halted by the larger leaf veins. The delicate, felt-like coating on the underside (hence the name 'mildew') is the sporulation of the oomycete — best seen in the morning or after a period of high air humidity. Over time the spots turn brown, dry out and merge, the leaf dies prematurely, which weakens the whole plant and lowers the yield. The disease is highly host-specialised: cucumbers and squashes are attacked by Pseudoperonospora cubensis, onion by Peronospora destructor, grapevine by Plasmopara viticola, and lettuce by Bremia lactucae — so infection of one species usually does not spread to unrelated crops.
AphidsSmall (1–3 mm) soft-bodied insects, green, black or pink, feeding in clusters on young shoots and the underside of leaves. They excrete sticky honeydew. The diagnostic feature that distinguishes aphids from other small sucking insects is the pair of siphunculi (tubular projections) at the rear of the abdomen together with a tail-like cauda; a single colony usually holds wingless forms (parthenogenetic females) alongside winged migrants that fly onto new plants in summer. In summer aphids reproduce parthenogenetically and viviparously over many generations, so the population builds up explosively; in autumn many species produce a sexual generation that lays overwintering eggs on the host, and host-alternating species move between a winter host (often a tree or shrub) and a summer host (a herbaceous plant). Feeding symptoms include curling, crinkling and distortion of young leaves, stunted growth, yellowing, and the shedding of buds and fruitlets. Abundant honeydew coats the leaves, and the sooty mould fungus that develops on it forms a black film which limits photosynthesis; the honeydew is fed on by ants, which in return defend the colony against predators. Aphids are also important vectors of plant viruses (mosaics among them), transmitting them from plant to plant even during a brief probing puncture.
Toxicity
| For whom | Level | Notes |
|---|---|---|
| Humans | Moderate | Contains cyanogenic glycosides — consumption may cause stomach upset. |
| Dogs | Moderate | — |
| Cats | Moderate | — |
| Horses | Moderate | — |
History and origin
Bigleaf hydrangea was brought to Europe from Japan at the turn of the 18th and 19th centuries. It quickly became one of the most popular ornamental shrubs for shaded corners of the garden. More precisely, the route to Europe had two stages: the first plants reached Kew in 1789 thanks to Joseph Banks, and these were a garden form of Chinese origin, while the wild Japanese forms arrived only with the collections of Philipp Franz von Siebold in the 1820s and 1830s. It was described scientifically by Carl Peter Thunberg in Flora Japonica (1784), initially as Viburnum macrophyllum; it was moved to the genus Hydrangea only in the 19th century. The genus name comes from the Greek words hydor (water) and angeion (vessel) and refers to the cup-like shape of the seed capsules. French nurseries at the turn of the 19th and 20th centuries had a strong influence on today's range of cultivars, especially Émile Mouillère in Vendôme, which produced some of the classic mophead cultivars. Later, breeding was taken over by German, Dutch and Swiss centers — the lacecap Teller series comes from Switzerland. In Germany the shrub became so widespread in cottage gardens that it is known there as Bauernhortensie, the farmer's hydrangea. In Japan, where it is native, ajisai flowers during the rainy season and is the theme of June flowering festivals at temples, among others in Kamakura.
Uses
For shaded borders, near patios and entrances, in large containers, and as cut and dried flowers. The best exposure is east or north, sheltered from the afternoon sun and from wind that dries out the large leaves. It is planted in April–May or in September, in a hole about 40 cm deep and at spacings of 100–150 cm; it is worth replacing the substrate with an acidic one (peat, bark, rhododendron soil) and mulching every year with pine bark, which holds moisture and, as it breaks down, slightly acidifies the top layer of soil — a real drop in pH in the root zone comes only from acidifying fertilizers and from replacing the substrate with an acidic mix. Rainwater is better for watering: hard tap water raises the pH and encourages chlorosis. In plantings it is combined with plants that share its requirements: hostas, ferns, astilbes and heucheras, and with acid-loving plants (rhododendrons, azaleas, pieris), as well as with Japanese maple, which likes the same sheltered, moist position. It looks good against the north wall of a house and at the edge of a group of trees. In a container it needs a large pot and an acidic substrate, because the root ball dries out there much faster than in the ground. For dried bouquets, individual flower heads are cut in late summer, once the sepals turn papery — but the shrub is not stripped of them: spent flower heads left over winter protect the flower buds, so the rest is cut only in spring. It is not suited to dry, sunny borders or to limestone soils.
Trivia
- To get blue flowers, gardeners water hydrangeas with an aluminum sulfate solution.
- Cultivars are divided into ball-shaped (mophead) and flat (lacecap) types.
- In the 1830s Philipp Franz von Siebold described Japanese hydrangeas under the name Hydrangea otaksa — in honor of his Japanese partner Kusumoto Taki, known as Otaki. Today it is a synonym of Hydrangea macrophylla.
- In Japan, a sweet infusion called amacha is made from the fermented leaves of the Japanese botanical variety (var. thunbergii) and is used on 8 April at the festival of the Buddha's birthday. This does not make bigleaf hydrangea an edible plant — it involves a narrow group of plants and special processing of the raw material, and mass poisonings after too concentrated an infusion have been recorded in Japan, so trying to prepare anything from hydrangea leaves on your own is dangerous.
Frequently asked questions
How do you get blue hydrangea flowers?
Blue color comes from acidic soil (pH below 5.5) with available aluminum. It can be maintained by watering the plant with an aluminum sulfate solution and using acidifying fertilizers.
Why isn't my hydrangea flowering?
The most common causes are pruning too hard or in fall (which removes flower buds) and frost damage to the buds. Bigleaf hydrangea blooms on the previous year's wood.
How much should hydrangea be watered?
A lot and regularly, especially in hot weather — the large leaves lose water quickly. The soil should stay consistently slightly moist, but not waterlogged.
How does bigleaf hydrangea differ from panicle hydrangea?
Bigleaf hydrangea (Hydrangea macrophylla) has thick, glossy leaves, ball-shaped or flat-topped (lacecap) flower clusters, and blooms on last year's wood, which is why it needs careful pruning. Panicle hydrangea (Hydrangea paniculata) has narrower, matte leaves, conical panicles, and blooms on the current year's growth, so it tolerates hard pruning in spring and is more frost-hardy. The flower color of panicle hydrangea does not depend on soil pH.
How do you protect bigleaf hydrangea for winter?
The shrub is hardy to zone 6a and frost rarely kills the whole plant — it mainly loses the flower buds formed in autumn. After the first frosts, mound a thick layer of bark, leaves or compost over the base, leave the spent flower heads on the shoots, and additionally cover young plants and those exposed to wind with horticultural fleece. Remove the cover gradually in spring, once hard frosts have passed, and prune only then, when it is clear which shoots have come through the winter. Container-grown shrubs need more attention, because the root ball freezes much faster in a pot than in the ground — wrap the container with a mat or burlap and move it against a wall, sheltered from the wind.
Sources
- Plants of the World Online (POWO)Database (GBIF, POWO…)
- RHS — Hydrangea macrophyllaInstitution / botanical garden
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