Hydrangea macrophylla

Hydrangea macrophylla is a species of flowering plant in the family Hydrangeaceae, native to Japan. It is a deciduous shrub growing to 2 m (7 ft) tall by 2.5 m (8 ft) broad with large heads of pink or blue flowers in summer and autumn. Common names include bigleaf hydrangea, French hydrangea, lacecap hydrangea, mophead hydrangea, and hortensia. It is widely cultivated in many parts of the world in many climates. It is not to be confused with H. aspera 'Macrophylla'.
The term macrophylla means 'large- or long-leaved'. The opposite leaves can grow to 15 cm (6 in) in length. They are simple, membranous, orbicular to elliptic and acuminate. They are generally serrated.
The inflorescence of Hydrangea macrophylla is a corymb, with all flowers placed in a plane or hemisphere, or even a whole sphere in cultivated forms. Two distinct types of flowers can be identified: central, non-ornamental, pentamerous ones, and peripheral, ornamental, tetramerous ones. The latter have sterile pistils with fertile stamen. The four sepals of decorative flowers have colors ranging from pale pink to red fuchsia purple to blue. The non-decorative flowers have five small greenish sepals and five small petals. Flowering begins in early summer and lasts until early winter. The fruit is a subglobose capsule.
Hydrangea macrophylla is native to East Asia. It is reported from seaside habitats as well as mountains in Japan, from Honshu southwards. This species has naturalized in China, Korea, Siberia, New Zealand and the Americas. It is an invasive species in the Azores and Madeira archipelagos.
Hydrangea macrophylla blooms can be blue, red, pink, light purple, or dark purple. The color is affected by soil pH. An acidic soil (pH below 7) will usually produce a flower colour closer to blue, whereas an alkaline soil (pH above 7) will produce flowers of a pink, or even a red colour. This is caused by a color change of the flower pigments in the presence of aluminium ions which can be taken up into hyperaccumulating plants. Scientists do not understand why this happens, whether it is due to predation or to attract pollinators.
In climates where Hydrangea macrophylla flowers, place in a mixed shrub border or at the back of a flower bed. Its rich foliage and large size make it a wonderful background for white or light colored flowers, even tall growing perennials and annuals. In warm climates H. macrophylla is good for adding a splash of early summer color to shady areas and woodland gardens. Minimal pruning is recommended for most prolific flowering. Flowers are easily air dried and are long lasting.
While Hydrangea macrophylla is not considered a particularly difficult plant to grow, it may fail to flower. This may be due to cold winter damage to the flower buds, not getting enough sunlight, too much nitrogen fertilizer, or pruning at the wrong time of year. H. macrophylla forms flower buds in late summer. As a result, pruning in late summer, fall or winter could remove potential flowers.
Although Hydrangea macrophylla is primarily grown outdoors, some cultivars are kept as houseplants under suitable conditions. Because of the low cost of potted plants, even experts may prefer to discard plants when they finish flowering rather than attempting to keep plants healthy indoors. H. macrophylla plants require lots of water and fertilitzer, so plants grown indoors require frequent watering and slow-release fertilizers due to the difficulties with growing them in containers. It is also quite difficult for a grower to produce a strong blue flower in a container and easier to produce pink or red blooms. Though they have a high water requirement the plants also require good drainage.
Phyllodulcin, hydrangenol, and their 8-O-glucosides, and thunberginols A and F can be found in H. macrophylla. Thunberginol B, the dihydroisocoumarins thunberginol C, D and E, the dihydroisocoumarin glycosides thunberginol G 3'-O-glucoside and (−)-hydrangenol 4'-O-glucoside and four kaempferol and quercetin oligoglycosides can be found in Hydrangeae Dulcis Folium, the processed leaves of H. macrophylla var. thunbergii. The leaves also contain the stilbenoid hydrangeic acid.
The various colors, such as red, mauve, purple, violet and blue, in H. macrophylla are developed from one simple anthocyanin, delphinidin 3-glucoside (myrtillin), which forms complexes with metal ions called metalloanthocyanins.
Lunularic acid, lunularin, 3,4′-dihydroxystilbene and a glycoside of lunularic acid have been found in the roots of H. macrophylla.
Hydrangine is another name for the coumarin umbelliferone, and may be responsible for the possible toxicity of the plant.
Amacha is a Japanese beverage made from fermented leaves of Hydrangea macrophylla var. thunbergii.
Hydrangeae Dulcis Folium is a drug made from the fermented and dried leaves of H. macrophylla var. thunbergii with possible antiallergic and antimicrobial properties. It also has a hepatoprotective activity by suppression of D-galactosamine-induced liver injury in vitro and in vivo.
Hydrangea macrophylla is included in the Tasmanian Fire Service's list of low flammability plants, indicating that it is suitable for growing within a building protection zone.
Leaf extracts of Hydrangea macrophylla are being investigated as a possible source of new chemical compounds with antimalarial activity. Hydrangeic acid from the leaves is being investigated as a possible anti-diabetic drug as it significantly lowered blood glucose, triglyceride, and free fatty acid levels in laboratory animals.
The two main types of H. macrophylla cultivars are called "mophead" and "lacecap".
Some popular hydrangea cultivars (those marked agm have gained the Royal Horticultural Society's Award of Garden Merit) include:
Yuan, Qi, H., Yang, S., Chu, Z., Zhang, G., & Liu, C. (2023). Role of delphinidin-3-glucoside in the sepal blue color change among Hydrangea macrophylla cultivars. Scientia Horticulturae, 313, 111902–. https://doi.org/10.1016/j.scienta.2023.111902