Is a genus of 70-75 species of plants with flowers native to South and East Asia (China, Japan, Korea, Himalayas and Indonesia) and the Americas. By far the greatest diversity of species is found in East Asia, particularly China, Japan and Korea. Most are shrubs 1 to 3 meters high, but some are small trees, and other lianas reach up to 30 m (98 feet) climbing the trees. They may be deciduous or evergreen, although the widely cultivated temperate species are deciduous.

Life cycle

Hydrangea flowers are produced from early spring to late autumn; they grow in flowerheads (corymbs or panicles) most often at the ends of the stems. Typically the flowerheads contain two types of flowers: small non-showy flowers in the center or interior of the flowerhead, and large, showy flowers with large colorful sepals (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 inflorescens, 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 rhododendrons and viburnums can appear, at first glance, similar to those of some hydrangeas.

Watering

Hydrangeas prefer well-drained, moist soil, but not wet; overwatering can cause hydrangeas to produce less flowers. Depending on your soil type, you will need to adjust how frequently and how much you water. Clay soil holds more water than sandy or loam soil types, and produces more runoff because it doesn’t allow as much water to soak in as a looser sandy soil. We recommend using a drip irrigation system, a soaker hose or hand watering the shrubs when the ground feels dry. If your hydrangeas are planted in an area that sees high temperatures, they may wilt a bit in the afternoon, but will revive when the temperatures cool down. You can assist with this by watering in the morning or evening when the wind is more still and the sun less hot. Using mulch is another great way of conserving water and keeping the ground cool. Mulched plants typically can go longer periods of time between watering than non-mulched plants.

Pruning and Care

 Endless Summer hydrangeas require very little pruning day-to-day, so you are able to simply enjoy the beautiful plants. These perennial hydrangeas bloom on growth from the current year as well as previous years, which allows for the re-blooming throughout the summer. If you prune too much, you will be removing potential blooms. If you prune to shape the plant or cut blooms for fresh hydrangea arrangements, be sure not to over-prune, or you will have less blooms next year. 

 https://en.wikipedia.org/wiki/Hydrangea

http://www.endlesssummerblooms.com/design-and-grow/planting-and-care