Editing Hydrangea

{{Short description|Genus of flowering plants}}
{{Redirect-several|Hydrangea|Hortensia}}
{{Automatic taxobox
|image=Hydrangea arborescens 139866012.jpg
|image_caption=''[[Hydrangea arborescens]]'' in Catoctin Creek Park & Nature Center, Maryland, USA
|taxon=Hydrangea
|authority=[[Jan Frederik Gronovius|Gronov.]] ex [[Carl Linnaeus|L.]]
|subdivision_ranks=Species
|subdivision=See text
|synonyms_ref=<ref name="30010546-2" >{{cite web |url=https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:30010546-2 |title=''Hydrangea'' Gronov. ex L. |website=Plants of the World Online |publisher=Board of Trustees of the Royal Botanic Gardens, Kew |date=2021 |access-date=17 September 2021 }}</ref>
|synonyms=
{{collapsible list|bullets = true
 |title={{small|synonymy}}
|''Adamia'' {{small|Wall.}}
|''Broussaisia'' {{small|Gaudich.}}
|''Calyptranthe'' {{small|(Maxim.) Nakai}}
|''Cardiandra'' {{small|Siebold & Zucc.}}
|''Cianitis'' {{small|Reinw.}}
|''Cornidia'' {{small|Ruiz & Pav.}}
|''Decumaria'' {{small|L.}}
|''Deinanthe'' {{small|Maxim.}}
|''Dichroa'' {{small|Lour.}}
|× ''Didrangea'' {{small|J.M.H.Shaw}}
|''Forsythia'' {{small|Walter}}
|''Heteromalla'' {{small|(Rehder) H.Ohba & S.Akiyama}}
|''Hortensia'' {{small|Comm. ex Juss.}}
|''Hydrangia'' {{small|L.}}
|''Macnemaraea'' {{small|Willemet}}
|''Pileostegia'' {{small|Hook.f. & Thomson}}
|''Platycrater'' {{small|Siebold & Zucc.}}
|''Sarcostyles'' {{small|C.Presl ex DC.}}
|''Schizophragma'' {{small|Siebold & Zucc.}}
}}
|type_species = ''[[Hydrangea arborescens]]'' L.<ref name = "IPNI">''Hydrangea'' | International Plant Names Index. (n.d.). Retrieved January 5, 2024, from https://www.ipni.org/n/30010546-2</ref>
}}

'''''Hydrangea''''' ({{IPAc-en|h|aɪ|ˈ|d|r|eɪ|n|dʒ|ə}}<ref>{{Cite Cambridge Dictionaries|hydrangea|access-date=15 September 2024}}</ref><ref>{{Cite Merriam-Webster|hydrangea|access-date=15 September 2024}}</ref> or {{IPAc-en|h|aɪ|ˈ|d|r|eɪ|n|dʒ|i|ə}}<ref>''Sunset Western Garden Book'', 1995: 606–607</ref>) is a [[genus]] of more than 70 species of [[Flowering plant|flowering plants]] [[native plant|native]] to Asia and the Americas. '''Hydrangea''' is also used as the [[common name]] for the genus; some (particularly ''[[Hydrangea macrophylla|H. macrophylla]]'') are also often called '''hortensia'''.<ref>{{cite web | title=Hydrangea macrophylla (H) | website=RHS | date=2025-02-04 | url=https://www.rhs.org.uk/plants/40792/hydrangea-macrophylla-(h)/details | access-date=2025-04-23}}</ref> The genus was first described from Virginia in North America,<ref>{{cite book | last=Linné | first=Carl von | last2=Salvius | first2=Lars | title=Caroli Linnaei ... Species plantarum :exhibentes plantas rite cognitas, ad genera relatas, cum differentiis specificis, nominibus trivialibus, synonymis selectis, locis natalibus, secundum systema sexuale digestas... | publisher=Impensis Laurentii Salvii | publication-place=Holmiae | year=1753 | doi=10.5962/bhl.title.669 | doi-access=free | url=https://www.biodiversitylibrary.org/itempdf/13829 | access-date=2025-04-23 | page=}}</ref> but by far the greatest species diversity is in eastern Asia, notably China, Korea, and Japan. Most are [[shrub|shrubs]] {{cvt|1-3|m}} tall, but some are small [[tree]]s, and others [[liana]]s reaching up to {{cvt|30|m|ft|-1}} by climbing up trees. They can be either [[deciduous]] or [[evergreen]], though the widely [[Horticulture|cultivated]] [[Temperate climate|temperate]] species are all deciduous.<ref>{{cite web |title=The United States National Arboretum: Hydrangea FAQ |url=http://www.usna.usda.gov/Gardens/faqs/hydrangeafaq2.html |access-date=27 November 2008 |archive-url=https://web.archive.org/web/20130516083220/http://www.usna.usda.gov/Gardens/faqs/hydrangeafaq2.html |archive-date=16 May 2013 |url-status=dead}}</ref>

The flowers of many hydrangeas act as natural [[pH indicator]]s, producing blue flowers when the soil is acidic and pink ones when the soil is alkaline.<ref>{{Cite web |date=2017-02-06 |title=Curious Chemistry Guides Hydrangea Colors |url=https://www.americanscientist.org/article/curious-chemistry-guides-hydrangea-colors |access-date=2024-05-27 |website=American Scientist |language=en}}</ref>

==Etymology==
''Hydrangea'' is derived from [[Ancient Greek language|Greek]] and means 'water vessel' (from {{lang|el|ὕδωρ}} ''húdōr'' "water" + {{lang|el|ἄγγος}} ''ángos'' or {{lang|el|ἀγγεῖον}} ''angeîon'' "vessel"),<ref name="hudorAGEL">{{cite web|url=https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Du(%2Fdwr |title=ὕδωρ |last1=Liddell |first1=Henry George |last2=Scott |first2=Robert |work=A Greek-English Lexicon |publisher=Perseus Digital Library |date= 1940 }}</ref><ref name="angosAGEL">{{cite web|url=https://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0057:entry=a)/ggos |title=ἄγγος |last1=Liddell |first1=Henry George |last2=Scott |first2=Robert |work=A Greek-English Lexicon |publisher=Perseus Digital Library |date= 1940 }}</ref><ref name="angeionAGEL">{{cite web|url=https://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0057:entry=a)ggei=on |title=αγγεῖον |last1=Liddell |first1=Henry George |last2=Scott |first2=Robert |work=A Greek-English Lexicon |publisher=Perseus Digital Library |date= 1940 }}</ref> in reference to the shape of its seed capsules.<ref name="gledhill">{{cite book|last=Gledhill |first= David |year= 2008 |title= The Names of Plants |publisher= Cambridge University Press |pages= 50, 206 |isbn=9780521866453}}</ref> The earlier name, ''Hortensia'', is a Latinised version of the French given name Hortense, honoring the French astronomer and mathematician [[Nicole-Reine Lepaute|Nicole-Reine Hortense Lepaute]].<ref>{{Cite web |url=https://en.oxforddictionaries.com/definition/hortensia |archive-url=https://web.archive.org/web/20171207135856/https://en.oxforddictionaries.com/definition/hortensia |url-status=dead |archive-date=December 7, 2017 |title=hortensia {{!}} Definition of hortensia in English by Oxford Dictionaries|website=Oxford Dictionaries {{!}} English |access-date=2017-12-07}}</ref> [[Philibert Commerson]] attempted to name the flower ''Lepautia'' or ''Peautia'' after Lepaute. However, the flower's accepted name later became ''Hortensia''. This led to people believing Lepaute's name was Hortense, but the Larousse remarks that this is erroneous, and that the name probably came from ''hortus'', garden.<ref name=Lynn>{{cite journal |last1=Lynn |first1=W. T. |title=Madame Lepaute |journal=The Observatory |date=2 January 1911 |volume=34 |pages=77–78 |bibcode=1911Obs....34...87L |url=https://articles.adsabs.harvard.edu/full/1911Obs....34...87L |access-date=8 November 2022}}</ref>

==Life cycle==
''Hydrangea'' [[flower]]s are produced from early spring to late autumn; they grow in flowerheads ([[corymb]]s or [[panicle]]s) most often at the ends of the stems. Typically the flowerheads contain two types of flowers: small non-showy fertile flowers in the center or interior of the flowerhead, and large, sterile showy flowers with large colorful [[sepal]]s (tepals). These showy flowers are often extended in a ring, or to the exterior of the small flowers. Plants in wild populations typically have few to none of the showy flowers, while cultivated hydrangeas have been bred and selected to have more of the larger type flowers.

There are two flower arrangements in hydrangeas with [[corymb]] style inflorescences, which includes the commonly grown "bigleaf hydrangea"—''Hydrangea macrophylla''. Mophead flowers are large round flowerheads resembling pom-poms or, as the name implies, the head of a mop. In contrast, lacecap flowers bear round, flat flowerheads with a center core of subdued, small flowers surrounded by outer rings of larger flowers having showy sepals or tepals. The flowers of some [[rhododendron]]s and [[viburnum]]s can appear, at first glance, similar to those of some hydrangeas.

==Colors and soil acidity==
[[File:Hydrangea Flower Color Based on Soil pH.jpg|thumb|Hydrangea flower color changes based on the pH in soil. As the graph depicts, soil with a pH of 5.5 or lower will produce blue flowers, a pH of 6.5 or higher will produce pink hydrangeas, and soil in between 5.5 and 6.5 will have purple hydrangeas.]] 
Hydrangea flower color can change based on the pH in soil. As the graph depicts, soil with a pH of 5.5 or lower will produce blue flowers, a pH of 6.5 or higher will produce pink hydrangeas, and soil in between 5.5 and 6.5 will have purple hydrangeas. White hydrangeas cannot be color-manipulated by soil pH because they do not produce pigment for color. In other words, while the hue of the inflorescence is variable dependent upon cultural factors, the color saturation is genetically predetermined.  In most species, the flowers are [[white]]. In some, however, (notably ''H. macrophylla''), they can be blue, red, or purple, with color saturation levels ranging from the palest of pinks, lavenders & powder blues, to deep, rich purples, reds, and royal blues. In these species, [[floral color change]] occurs due to the availability of [[aluminium]] [[ion]]s, a variable which itself depends upon the [[soil pH]].<ref>{{cite web |url=http://www.caes.uga.edu/Publications/pubDetail.cfm?pk_id=7829 |title=Publications - UGA Cooperative Extension |website=www.caes.uga.edu |access-date=31 May 2018}}</ref><ref>{{cite web |url=http://www.usna.usda.gov/Gardens/faqs/hydrangeafaq2.html |title=USDA: Hydrangea Questions and Answers |access-date=31 May 2018 |archive-url=https://web.archive.org/web/20130516083220/http://www.usna.usda.gov/Gardens/faqs/hydrangeafaq2.html |archive-date=16 May 2013 |url-status=dead}}</ref> For ''H. macrophylla'' and ''H. serrata'' cultivars, the flower color can be determined by the relative acidity of the soil: an acidic soil (pH below 7), will have available aluminium ions and typically produce flowers that are blue to purple,<ref>{{Cite EB1911|wstitle=Hydrangea |volume=14 |page=34; see line five |quote=...but by the influence of sundry agents in the soil, such as alum or iron, they become changed to blue}}.</ref> whereas an alkaline soil (pH above 7) will tie up aluminium ions and result in pink or red flowers. This is caused by a color change of the [[flower pigment]]s in the presence of aluminium ions which can be taken up into [[Phytoremediation, Hyperaccumulators|hyperaccumulating plant]]s.<ref>{{cite web |title=Hydrangea Plants |url=http://www.whiteflowerfarm.com/hydrangea-shrubs-spring.html}}</ref>

==Species==
[[File:Hydrangea paniculata - flower view 01.jpg|thumb|right|''[[Hydrangea paniculata]]'']]
97 species are accepted.<ref name = powo>{{cite web |title=''Hydrangea'' Gronov. ex L. |url=https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:30010546-2 |website=[[Plants of the World Online]] |publisher=[[Royal Botanic Gardens, Kew]] |access-date=25 April 2025}}</ref>
{{div col}}
*''[[Hydrangea acuminata]]'' {{small|Siebold & Zucc.}}
*''[[Hydrangea albostellata]]'' {{small|Samain, Najarro & E.Martínez}}
*''[[Hydrangea alternifolia]]'' {{small|Siebold}}
*''[[Hydrangea × amagiana]]'' {{small|Makino}}
*''[[Hydrangea amamiohsimensis]]'' {{small|(Koidz.) Y.De Smet & Granados}}
*''[[Hydrangea ampla]]'' {{small|(Chun) Y.De Smet & Granados}}
*''[[Hydrangea anomala]]'' {{small|D.Don}} – (climbing hydrangea) Himalaya, southwest China
*''[[Hydrangea arborescens]]'' {{small|L.}} – (smooth hydrangea) eastern North America
*''[[Hydrangea arguta]]'' {{small|(Gaudich.) Y.De Smet & Granados}}
*''[[Hydrangea aspera]]'' {{small|Buch.-Ham. ex D.Don}} – China, Himalaya
*''[[Hydrangea asterolasia]]'' {{small|Diels}}
*''[[Hydrangea barbara]]'' {{small|(L.) Bernd Schulz}}
*''[[Hydrangea bifida]]'' {{small|(Maxim.) Y.De Smet & Granados}}
*''[[Hydrangea breedlovei]]'' {{small|Samain, Najarro & E.Martínez}}
*''[[Hydrangea bretschneideri]]''  {{small|Dippel}} – China
*''[[Hydrangea caerulea]]''  {{small|(Stapf) Y.De Smet & Granados}}
*''[[Hydrangea carroniae]]''  {{small|Samain & E.Martínez}}
*''[[Hydrangea chungii]]'' {{small|Rehder}} – China
*''[[Hydrangea cinerea]]'' {{small|Small}} – (ashy hydrangea) eastern United States
*''[[Hydrangea coenobialis]]'' {{small|Chun}} – China
*''[[Hydrangea corylifolia]]'' {{small|(Chun) Y.De Smet & Granados}}
*''[[Hydrangea crassa]]'' {{small|(Hand.-Mazz.) Y.De Smet & Granados}}
*''[[Hydrangea daimingshanensis]]'' {{small|(Y.C.Wu) Y.De Smet & Granados}}
*''[[Hydrangea davidii]]'' {{small|Franch.}} – China
*''[[Hydrangea densifolia]]'' {{small|(C.F.Wei) Y.De Smet & Granados}}
*''[[Hydrangea diplostemona]]'' {{small|(Donn.Sm.) Standl.}}
*''[[Hydrangea fauriei]]'' {{small|(Hayata) Y.De Smet & Granados}}
*''[[Hydrangea febrifuga]]'' {{small|(Lour.) Y.De Smet & Granados}} (syn. ''Dichroa febrifuga'') – central & southern China to Malesia and New Guinea
*''[[Hydrangea glaucescens]]'' {{small|(Rehder) Y.De Smet & Granados}} – China, Myanmar and Vietnam
*''[[Hydrangea gracilis]]'' {{small|W.T.Wang & M.X.Nie}} – China
*''[[Hydrangea heteromalla]]'' {{small|D.Don}} – Himalaya, west and north China
*''[[Hydrangea hirsuta]]'' {{small|(Gagnep.) Y.De Smet & Granados}}
*''[[Hydrangea hirta]]'' {{small|(Thunb.) Siebold}} – Japan
*''[[Hydrangea hwangii]]'' {{small|J.M.H.Shaw}}
*''[[Hydrangea hydrangeoides]]'' {{small|(Siebold & Zucc.) Bernd Schulz}} – [[Ulleungdo]], Japan, Kurils
*''[[Hydrangea hypoglauca]]'' {{small|Rehder}} – China
*''[[Hydrangea integrifolia]]'' {{small|Hayata}} – China
*''[[Hydrangea involucrata]]'' {{small|Siebold}} – Japan, Taiwan
*''[[Hydrangea jelskii]]'' {{small|Szyszył.}} – Andes
*''[[Hydrangea kawagoeana]]'' {{small|Koidz.}}
*''[[Hydrangea kwangsiensis]]'' {{small|Hu}} – China
*''[[Hydrangea kwangtungensis]]'' {{small|Merr.}} – China
*''[[Hydrangea lalashanensis]]'' {{small|S.S.Ying}}
*''[[Hydrangea lingii]]'' {{small|G.Hoo}} – China
*''[[Hydrangea linkweiensis]]'' {{small|Chun}} – China
*''[[Hydrangea liukiuensis]]'' {{small|Nakai}}
*''[[Hydrangea lobbii]]'' {{small|Maxim.}}
*''[[Hydrangea longifolia]]'' {{small|Hayata}} – China
*''[[Hydrangea longipes]]'' {{small|Franch.}} – western China
*''[[Hydrangea luteovenosa]]'' {{small|Koidz.}}
*''[[Hydrangea macrocarpa]]'' {{small|Hand.-Mazz.}} – China
*''[[Hydrangea macrophylla]]'' {{small|(Thunb.) Ser.}} – (bigleaf hydrangea) southeast Japan, southern China
*''[[Hydrangea mangshanensis]]'' {{small|C.F.Wei}} – China
*''[[Hydrangea marunoi]]'' {{small|Tagane & S.Fujii}}
*''[[Hydrangea mathewsii]]'' {{small|Briq.}}
*''[[Hydrangea megalocarpa]]'' {{small|(Chun) J.M.H.Shaw}}
*''[[Hydrangea minamitanii]]'' {{small|(H.Ohba) Yahara}}
*''[[Hydrangea × mizushimarum]]'' {{small|H.Ohba}}
*''[[Hydrangea moellendorffii]]'' {{small|Hance}}
*''[[Hydrangea mollissima]]'' {{small|(Merr.) Y.De Smet & Granados}}
*''[[Hydrangea nahaensis]]'' {{small|Samain & E.Martínez}}
*''[[Hydrangea nebulicola]]'' {{small|Nevling & Gómez Pompa}}
*''[[Hydrangea obtusifolia]]'' {{small|(Hu) Y.De Smet & Granados}}
*''[[Hydrangea ofeliae]]'' {{small|Sodusta & Lumawag}}
*''[[Hydrangea otontepecensis]]'' {{small|Samain & E.Martínez}}
*''[[Hydrangea paniculata]]'' {{small|Siebold}} – (panicled hydrangea) eastern China, Japan, Korea, Sakhalin
*''[[Hydrangea peruviana]]'' {{small|Moric. ex Ser.}} – Costa Rica and Panama, Andes
*''[[Hydrangea petiolaris]]'' {{small|Siebold & Zucc.}} – (climbing hydrangea) Japan, Korea, Sakhalin
*''[[Hydrangea pingtungensis]]'' {{small|S.S.Ying}}
*''[[Hydrangea platyarguta]]'' {{small|Y.De Smet & Samain}}
*''[[Hydrangea pottingeri]]'' {{small|Prain}} (synonym ''[[Hydrangea chinensis]]''  {{small|Maxim.}}) – Arunachal Pradesh, Myanmar, southeastern China, and Taiwan
*''[[Hydrangea preslii]]'' {{small|Briq.}}
*''[[Hydrangea quercifolia]]'' {{small|W.Bartram}} – (oakleaf hydrangea) southeast United States
*''[[Hydrangea radiata]]'' {{small|Walter}} – (silverleaf hydrangea) southeast United States
*''[[Hydrangea robusta]]'' {{small|Hook.f. & Thomson}} – China, Himalaya
*''[[Hydrangea sargentiana]]'' {{small|Rehder}} – western China
*''[[Hydrangea scandens]]'' {{small|(L.f.) Ser.}} – southern Japan south to the Philippines
*''[[Hydrangea serrata]]'' {{small|(Thunb.) Ser.}} – Japan, Korea
*''[[Hydrangea serratifolia]]'' {{small|(Thunb.) Ser.}} – Chile, western Argentina
*''[[Hydrangea sikokiana]]'' {{small|Maxim.}}
*''[[Hydrangea sousae]]'' {{small|Samain, Najarro & E.Martínez}}
*''[[Hydrangea steyermarkii]]'' {{small|Standl.}}
*''[[Hydrangea strigosa]]'' {{small|Rehder}} – China
*''[[Hydrangea stylosa]]'' {{small|Hook.f. & Thomson}} – China
*''[[Hydrangea taiwaniana]]'' {{small|Y.C.Liu & F.Y.Lu}}
*''[[Hydrangea tapalapensis]]'' {{small|Samain, Najarro & E.Martínez}}
*''[[Hydrangea tarapotensis]]'' {{small|Briq.}} – Andes
*''[[Hydrangea tomentella]]'' {{small|(Hand.-Mazz.) Y.De Smet & Granados}}
*''[[Hydrangea × versicolor]]'' {{small|(Fortune) J.M.H.Shaw}}
*''[[Hydrangea viburnoides]]'' {{small|(Hook.f. & Thomson) Y.De Smet & Granados}}
*''[[Hydrangea wallichii]]'' {{small|J.M.H.Shaw}}
*''[[Hydrangea xanthoneura]]'' {{small|Diels}} – China
*''[[Hydrangea xinfeniae]]'' {{small|W.B.Ju & J.Ru}}
*''[[Hydrangea yaoshanensis]]'' {{small|(Y.C.Wu) Y.De Smet & Granados}}
*''[[Hydrangea yayeyamensis]]'' {{small|Koidz.}}
*''[[Hydrangea × ytiensis]]'' {{small|(J.M.H.Shaw) J.M.H.Shaw}}
*''[[Hydrangea yunnanensis]]'' {{small|Rehder}}
*''[[Hydrangea zhewanensis]]'' {{small|P.S.Hsu & X.P.Zhang}} – China
{{div col end}}

==Fossil record==
[[File:Hydrangea knowltoni as Hydrangea bendirei USNM P36979 img3.jpg|thumb|right|''[[Hydrangea knowltoni]]'']]
{{extinct}}''[[Hydrangea alaskana]]'' is a fossil species recovered from [[Paleogene]] strata at Jaw Mountain Alaska.<ref>{{cite journal |last=Hollick |first=Arthur |year=1925 |title=A New Fossil Species of Hydrangea |journal=Bulletin of the Torrey Botanical Club |volume=52 |issue=1 |pages=21–22 |doi=10.2307/2479996 |jstor=2479996}}</ref> †''[[Hydrangea knowltoni]]'' has been described from leaves and flowers recovered from the Miocene [[Langhian]] [[Latah Formation]] of the inland Pacific Northwest United states. The related Miocene species †''[[Hydrangea bendirei]]'' is known to from the [[Mascall Formation]] in Oregon, and †''[[Hydrangea reticulata]]'' is documented from the [[Weaverville Formation]] in California.<ref name="Knowlton1926">{{cite report |last1=Knowlton |first1=F.H. |year=1926 |chapter=Flora of the Latah Formation of Spokane, Washington, and Coeur d'Alene, Idaho |title=Shorter contributions to general geology, 1925 |series=Professional Paper |publisher=United States Geological Survey |volume=140 |pages=17–55, plates VIII-XXXI |doi=10.3133/pp140A |url=https://pubs.usgs.gov/pp/0140a/report.pdf}}</ref><ref name="Columbia1959">{{cite book |last1=Chaney |first1=R. |last2=Axelrod |first2=D. |year=1959 |title=Miocene Floras of the Columbia Plateau: Part II. Systematic Considerations, by Ralph W. Chaney and Daniel I. Axelrod |publisher= Carnegie Institution of Washington |pages=1–226}}{{HathiTrust Catalog|uc1.c099384505|Miocene Floras of the Columbia Plateau}}</ref>

Four [[fossil]] seeds of †''[[Hydrangea polonica]]'' have been extracted from [[borehole]] samples of the [[Middle Miocene]] fresh water deposits in [[Nowy Sacz]] Basin, [[West Carpathians]], [[Poland]].<ref>Łańcucka-Środoniowa M.: Macroscopic plant remains from the freshwater Miocene of the Nowy Sącz Basin (West Carpathians, Poland) [Szczątki makroskopowe roślin z miocenu słodkowodnego Kotliny Sądeckiej (Karpaty Zachodnie, Polska)]. Acta Palaeobotanica 1979 20 (1): 3-117.</ref>

==Cultivation and uses==
Hydrangeas are popular [[ornamental plant]]s, grown for their large flowerheads, with ''[[Hydrangea macrophylla]]'' being by far the most widely grown. It has over 600 named [[cultivar]]s, many selected to have only large sterile flowers in the flowerheads. ''Hydrangea macrophylla'', also known as bigleaf hydrangea, can be broken up into two main categories; mophead hydrangea and lacecap hydrangea. Some are best pruned on an annual basis when the new leaf buds begin to appear. If not pruned regularly, the bush will become very "leggy", growing upwards until the weight of the stems is greater than their strength, at which point the stems will sag down to the ground and possibly break. Other species only flower on "old wood". Thus, new wood resulting from pruning will not produce flowers until the following season.

The following [[cultivars]] and species have gained the [[Royal Horticultural Society]]'s [[Award of Garden Merit]] under the synonym ''Schizophragma'':<ref>{{cite web |url=https://www.rhs.org.uk/plants/pdfs/agm-lists/agm-ornamentals.pdf |title=AGM Plants - Ornamental |date=July 2017 |page=96 |publisher=Royal Horticultural Society |access-date=6 November 2018}}</ref> 
*[[Hydrangea hydrangeoides|''S. hydrangeoides'' var. ''concolor'']] 'Moonlight'<ref name=RHSPF>{{cite web |url=https://www.rhs.org.uk/Plants/110847/i-Schizophragma-hydrangeoides-i-var-i-concolor-i-Moonlight/Details |title=RHS Plantfinder - ''Schizophragma hydrangeoides'' var. ''concolor'' 'Moonlight' |access-date=6 November 2018}}</ref> 
*[[Hydrangea hydrangeoides|''S. hydrangeoides'' var. ''hydrangeoides'']] 'Roseum'<ref>{{cite web |title=RHS Plant Selector - ''Schizophragma hydrangeoides'' var. ''hydrangeoides'' 'Roseum' |url=http://apps.rhs.org.uk/plantselector/plant?plantid=1804 |access-date=3 June 2013}}</ref>
*''[[Hydrangea glaucescens|S. integrifolium]]''<ref>{{cite web |title=RHS Plant Selector - ''Schizophragma integrifolium'' |url=https://www.rhs.org.uk/Plants/16816/Schizophragma-integrifolium/Details |access-date=5 March 2021}}</ref>

Hydrangea root and rhizome are indicated for the treatment of conditions of the urinary tract in the [[Physicians' Desk Reference]] for Herbal Medicine and may have diuretic properties.<ref>PDR for Herbal Medicine 3rd Edition Page 453</ref> Hydrangeas are moderately toxic if eaten, with all parts of the plant containing [[cyanogenic glycoside]]s.<ref>{{cite web |url=http://www.aspca.org/pet-care/poison-control/plants/hills-of-snow.html |title=Hills of Snow |access-date=31 May 2018}}</ref> ''[[Hydrangea paniculata]]'' is reportedly sometimes smoked as an intoxicant, despite the danger of illness and/or death due to the [[cyanide]].<ref>{{cite web |url=http://www.erowid.org/herbs/hydrangea/hydrangea.shtml |title=Erowid Hydrangea Vault |website=www.erowid.org |access-date=31 May 2018}}</ref><ref>{{cite news |url=https://www.theguardian.com/world/2014/feb/06/high-danger-hydrangea-french-police-hunt-gang |title=High danger hydrangea? French police hunt gang peddling 'cheaper weed' |first=Kim |last=Willsher |date=6 February 2014 |newspaper=the Guardian |access-date=31 May 2018}}</ref>

The flowers on a hydrangea shrub can change from blue to pink or from pink to blue from one season to the next depending on the acidity level of the soil.<ref>{{cite web |url=https://www.gardenista.com/posts/everything-need-know-hydrangeas/# |title=Everything You Need to Know About Hydrangeas |website=www.gardenista.com |access-date=15 June 2018 |date=2018-06-10}}</ref> Adding organic materials such as coffee grounds and citrus peel will increase acidity and turn hydrangea flowers blue.<ref>{{cite web |url=https://www.gardenista.com/posts/magic-trick-how-to-make-your-hydrangea-change-color/# |title=Hydrangeas: How To Change Color from Pink to Blue |website=www.gardenista.com |access-date=15 June 2018 |date=2016-05-10}}</ref>
A popular pink hydrangea called Vanilla Strawberry has been named "Top Plant" by the American Nursery and Landscape Association.

A hybrid "Runaway Bride Snow White", from Japan, won ''Plant of the Year'' at the 2018 RHS [[Chelsea Flower Show]].<ref>{{cite web |url=http://www.goodhousekeeping.co.uk/lifestyle/gardening-advice/hydrangeas-chelsea-plant-of-the-year# |title=This plant has been named 'plant of the year' at the Chelsea Flower Show |access-date=31 May 2018 |date=2018-05-22}}</ref>

===In culture===
In Japan, ''[[Amacha|ama-cha]]'' ({{lang|ja|甘茶}}), meaning sweet tea, is another herbal tea made from ''[[Hydrangea serrata]]'', whose leaves contain a substance that develops a sweet taste ([[phyllodulcin]]). For the fullest taste, fresh leaves are crumpled, steamed, and dried, yielding dark brown tea leaves. Ama-cha is mainly used for ''kan-butsu-e'' (the [[Buddha]] bathing ceremony) on April 8 every year—the day thought to be Buddha's birthday in Japan. During the ceremony, ama-cha is poured over a statue of Buddha and served to people in attendance. A legend has it that on the day Buddha was born, nine [[dragon]]s poured [[Amrita]] over him; ama-cha is substituted for Amrita in Japan.

In [[Korean tea]], ''[[Hydrangea serrata]]'' is used for an [[herbal tea]] called ''sugukcha'' ({{lang|ko|수국차}}) or ''isulcha'' ({{lang|ko|이슬차}}).

The pink hydrangea has risen in popularity all over the world, especially in Asia. The given meaning of pink hydrangeas is popularly tied to the phrase "you are the beat of my heart," as described by the celebrated Korean florist Tan Jun Yong, who was quoted saying, "The light delicate blush of the petals reminds me of a beating heart, while the size could only match the heart of the sender!"<ref>{{cite web |url=http://www.rollmagazine.com/archive/oct11/articles/garden.php |title=Hydrangeas, Hydrangeas, Hydrangeas - Roll Gardening & Green :: Roll Magazine: Creative Living in the Hudson Valley |website=www.rollmagazine.com |access-date=31 May 2018}}</ref>

''Hydrangea quercifolia'' was declared the official state wildflower of the U.S. state of [[Alabama]] in 1999.<ref>State Botanical SymbolsBy Alan McPherson, p.3</ref>

Hydrangeas were used by the [[Cherokee]] people of what is now the Southern U.S. as a mild diuretic and cathartic; it was considered a valuable remedy for stone and gravel in the bladder.<ref name="Library of Congress">{{cite book |last1=Hylton |first1=William H. |title=The Rodale herb book: how to use, grow, and buy nature's miracle plants |date=1974 |publisher=Rodale Press Book Division |location=Emmaus, Pa. |isbn=0-87857-076-4 |page=474 |oclc=610291480 |edition=Eighteenth Printing — September 1979 |url=https://www.worldcat.org/oclc/610291480 }}</ref>

[[Extrafloral nectaries]] were reported on hydrangea species by Zimmerman 1932, but Elias 1983 regards this as "doubtful".<ref>{{cite journal |date=2012-10-18 |first1=Marjorie G. |last1=Weber |first2=Kathleen H. |last2=Keeler |title=The phylogenetic distribution of extrafloral nectaries in plants |pages=1251–1261 |doi=10.1093/aob/mcs225 |journal=Annals of Botany |eissn=1095-8290 |volume=111 |issue=6|pmc=3662505 }}</ref>

<!-- ===Bee-friendliness===
Hydrangea variants vary in bee-friendliness and their ability to feed pollinators. In general, common hydrangeas are not bee-friendly because their flowers are sterile, e.g. ''Hydrangea macrophylla hortensis'' (''mophead'') and ''H. paniculata'' (''limelight'').
Those that give food for bees and pollinators are: 
* ''Hydrangea anomala petiolaris''
* ''Hydrangea arborescens'': Smooth hydrangeas are versatile and spectacular, and can be used in a variety of landscape settings, including foundation plantings, perennial gardens, hedges, cut flower gardens, naturalising, pollinator, and wildlife gardens.
* ''Hydrangea aspera'': 
* ''Hydrangea mycrophylla'': Bigleaf hydrangeas are classic choices for flower gardens, cottage gardens, and seaside plantings. They can also be used for low hedges or edging, and they offer a splash of color to foundation plantings.
* ''Hydrangea paniculata'' (''grandiflora''): Panicle hydrangeas are the most sun-tolerant and wilt-resistant of the hydrangeas. It's perfect for Specimen plantings, mixed borders, and mass plantings. It can be used as a hedge or a screen. Excellent for both fresh and dried cut flowers.
* ''Hydrangea quercifolia'': Oakleaf hydrangea blooms on old growth. It thrives in damp, well-drained environments. In colder climates, winter protection may be required. Shrub with a deciduous appearance. Apply a slow-release fertiliser formulated for trees and shrubs in the early spring. -->

==Gallery==
<gallery>
File:Hortensiapink.JPG|''[[Hydrangea macrophylla]]''
File:Hydrangea close up.jpg|Hydrangea flowers close up.
File:Pink Hydrangea Flowers.jpg|Flowers
File:Hydrangea-heads-pale.png|''Hydrangea macrophylla'', flowers
File:Blue Hydrangea.jpg|''Hydrangea macrophylla'', flowers
File:Hydrangea redoute.JPG|''Hydrangea sp'' painted by the botanical artist [[Redouté]].
File:Hydrangea quericifolia2.jpg|''Hydrangea quercifolia''
File:Hydrangea leaves.jpg|''Hydrangea macrophylla'', leaves
File:Wild hydrangea var annabelle.jpg|Wild Hydrangea v. Annabelle<br />''Hydrangea arborescens''
File:Hydrangea arborescens.jpg|Wild Hydrangea v. Annabelle<br />''Hydrangea arborescens''
File:Hydrangea arborescens annabelle.JPG|8" Annabelle Hydrangea Bloom. ''Hydrangea arborescens''.
File:Hydrangea-aspera-zoo-cgn-07074-mutante.jpg|''Hydrangea aspera ssp. sargentiana''
File:BlueHydrangea.JPG
File:Hydrangea paniculata IMG 6629.JPG|''[[Hydrangea paniculata]]''
File:Hydranchia.JPG|Hydrangea flowers from Kerala, India
File:Hydrangeas corner.JPG|Hydrangeas in front of the Office de Tourisme Building in Chartres, France
File:Hydrangea-08-10-08.JPG|Hydrangea flowers at the "[[Cerro El Avila]]" National Park, Venezuela
File:Hydrangeea.jpg|Hydrangea flowers, Srinagar, Kashmir, India
File:Hydrangea flowers in the rain.jpg|Hydrangea flowers
File:Petrópolis - Cidade das Hortências e do Russo - Nevoeiro.jpg|Hydrangea flowers in [[Petrópolis]], Brazil
File:Lagonegro3.jpg|Hydrangeas near the Black Lake of [[Gramado]], southern Brazil
File:Hydrangea-flower.jpg|Purple hydrangea flowers
File:Hydrangea arborescens leaf.jpg|''Hydrangea arborescens'' leaf
File:Hydrangea summer garden.jpg
File:Hydrangea flower white.jpg
File:Hydrangea flower summer garden.jpg
File:Wilted hydrangea.jpg
File:Hydrangea flower 3.jpg|Flower of hydrangea
File:Hydrangea flower 5.jpg|Flower of hydrangea
File:Vein sceleton hydrangea ies.jpg|Vein structure of a hydrangea leaf
File:Hydrangea arborescens (Smooth Hydrangea).jpg|Hydrangea arborescens (Smooth Hydrangea) in [[Calgary]], [[Canada]]
</gallery>

==Diseases==
{{Main article|List of hydrangea diseases}}

==References==
{{EB1911|wstitle=Hydrangea |volume=14 |page=34}}
{{Reflist}}

==External links==
* {{commons category-inline}}
*[http://www.erowid.org/herbs/hydrangea/hydrangea.shtml erowid.org]
*[http://www.efloras.org/florataxon.aspx?flora_id=110&taxon_id=115977 Flora of Nepal: ''Hydrangea'' species list]
*[https://web.archive.org/web/20081209052446/http://www.urbanext.uiuc.edu/shrubselector/search_results.cfm?q=hydrangea Hydrangea – selecting shrubs]
*[https://web.archive.org/web/20070927090002/http://www.botanik.de/mendel/image-galleries/blumen/hortensien Hydrangea species and hybrids]
*[http://geekgardener.in/2010/08/07/propagating-hydrangea-from-cuttings/ Propagating Hydrangeas]
*[https://web.archive.org/web/20161028153620/http://www.bgci.org/ourwork/Hydrangeas Red Listing of Threatened Hydrangeas]

{{Taxonbar|from=Q155997}}
{{Authority control}}

[[Category:Hydrangea| ]]
[[Category:Cornales genera]]
[[Category:Christmas plants]]
[[Category:Asterid genera]]