Hydrangeas are large flowering bushes native to the Northern Hemisphere. There are around 23 species in the Hydrangea genus, with around five in common domestic cultivation. The most common species used in gardens is Hydrangea macrophylla, also called French or Bigleaf Hydrangea. When most people think of hydrangeas, they visualize cultivars of this abundant species.
While most hydrangeas are flowering shrubs or bushes, some are actually climbing species. In all cases, hydrangeas have large, simple leaves and big clusters of flowers which may be white, pink, purple, red, or blue, depending on cultivar and soil conditions. Hydrangeas are easy to prune and shape, and in rich soil, they thrive, developing vigorous growth habits and quickly dominating their corner of the garden.
The flower colors of H. macrophylla is variable because the plants respond to the mineral and pH balance of the soil. Acidic soils produce blue flowers, while basic soils develop white flowers. Soil with a neutral pH will produce pink to purple flowers, and the flower color can be further influenced by the minerals in the soil, the amount of fertilizer the plant gets, and how healthy it is. Healthy plants tend to have very rich color saturation in their flowers, while unhealthy plants develop pallid, faded flowers.
Hydrangeas grow through USDA zone eight, and they require very rich, fertile soil, along with lots of water and full sun. In regions where the winter weather gets chilly, it can be a good idea to wrap hydrangeas at night to prevent frostbite, as freezing temperatures can damage new growth, inhibiting flowering and making it difficult for the plant to thrive. Particularly high-quality hydrangeas can be propagated from cuttings, for gardeners who are experienced at taking cuttings.
Hydrangeas require annual pruning, typically after all of the flowers have died off in the fall. Pruning helps the bush keep its shape, and prevents the development of long branches which could bend or break under the weight of flower clusters. Pruning is not advised in the Spring, as it can damage emerging flower clusters and shock the plant, preventing it from producing flowers for the year.
The flowers of hydrangeas make excellent dried flowers, and they are not uncommon in dried flower arrangements. Hydrangeas also do very well as cut flowers, enduring for weeks if they are kept in a vase with a little bit of nutrition.