Hydrangea

Hydrangeas have been cultivated in western gardens since the first American species were brought to England in the 1730s. Hydrangea macrophylla, the common, big-leaf hydrangea has been known by gardeners in its native land of Japan for many hundreds of years and grown in its many forms. There it has been treasured not only for the beauty of flowers and foliage, but also used as an herb, certain serrata forms having long been popular to create a sweet herbal tea. In the West, the large-leaved Hydrangea macrophylla intrigued French plant breeders at the turn of the last century. A few, like Lemoine, Mouillère, and Cayeux began raising new seedlings and charming the public with the beauty of young pot plants in full bloom, with their large, domed heads of pink, blue or white flowers. Today the potted hydrangea is almost a symbol in France of Mother's Day.

With the late twentieth century came a renewed interest in lacecap forms of Hydrangea macrophylla, and European breeders again produced an exceptional range of colors in this wild floral form. As Lacecaps have grown in popularity so have the more delicate cousins of the Macrophyllas, the Serratas, and many cultivars that originated in Japan have been brought back from the Orient by modern day plant collectors to grace our woodland gardens and satisfy a taste for the subtlety of these plants.
Interest has also grown over the native American species Arborescens and Quercifolia and new forms of these types are issuing from the hands of collectors and breeders each year. The genus Hydrangea is undergoing a revival of interest which is much deserved, and we hope to be able to contribute by providing clear and accurate information, and drawing attention to the historical connections between hydrangeas and history.
Much has been revealed about the story of Hydrangeas in recent years through the efforts of Corinne Mallet who has gathered together a French National collection of hydrangeas rivaling the famous rose collection of Empress Josephine. Her three books have given a historical perspective on this group of garden plants for which we are all very grateful.
Culture
In general hydrangeas want two things, moisture and shade. However too much of either is not a good thing. An oft-made mistake is the placement of Hydrangeas in too heavy a shade. Most are happier with a good dose of direct sun, dappled all day or with a morning sun exposure. Even Paniculata and Arborescens which are sun loving look better in flower and leaf if given a shady respite in the afternoon. No hydrangeas tolerate drought, though the thirstiest are the big leaved Macrophyllas that transpire rapidly on hot summer days and can wilt even when the soil about them is moist. Soils which are kept overly wet can compact, lose aeration and ultimately damage the Hydrangeas for whom the extra water was intended.
Soils should be well amended so as to accommodate the very fine root systems, and to preserve moisture. And, hydrangeas benefit from organic mulches and annual feeding though they can be quite successful without additional fertilizers. Pay attention to the soil pH! Hydrangeas tolerate a range of pH from 5.0 to 7.5, right into the alkaline range, and we are often adjusting the soil pH to alter flower color. But too high a pH can be detrimental to the plants; watch for signs of chlorosis or yellowing leaves, which can indicate a soil too alkaline for the proper uptake of nutrients. For more specific guidance on each group, don't miss our comments on culture under each class description.
Color in Hydrangea macrophylla & serrata
One fact that is widely known about Hydrangea macrophylla and its cultivars is that they can change color. This mutability is perhaps responsible for why for many decades hydrangeas have been offered by nurseries generically, and not by named cultivars, as roses have always been. It has been assumed that all hydrangeas are alike and if you want different colors, you need merely apply different chemicals which affect flower color. In fact there is a wide range of types of Hydrangea macrophylla, and color is ultimately determined more by variety than by what we do to the soils they grow in. White forms of H. macrophylla, like Mme. E. Mouillère, are always white, though some can be tinted with pale pink or blue. And, white Lacecaps will normally have colored fertile flowers which will color in the blue spectrum or the pink spectrum depending upon soil conditions. A wide range of depth of color exists in the pink and blue cultivars ranging from blush pink and robin's-egg blue to brick red and cobalt blue. The depth of color is entirely dependant on the cultivar. Otaksa, for example, will never reach a rich deep color, no matter how much you may pile on the chemicals. And some hydrangeas refuse to be changed to clear blue, like Geoffrey Chadbund, making a royal purple flower at best, when treated. Likewise, many features that distinguish varieties are not interchangeable. Some are very compact growers, like Hornli, and others very large, like Blue Wave. Some varieties have large floral heads, like Otaksa, and some very small, like Miss Belgium. As you explore the world of hydrangeas you will discover their distinctiveness and their wide range of beauty.
Changing color in Hydrangeas: Two factors affect the color in Hydrangea macrophylla cultivars, soil acidity and the presence of aluminum in the soil. Flowers can be made to 'blue' only when aluminum is present in the soil. Most soils contain aluminum, although if it is absent we can add it in the form of aluminum sulphate; however if the soil is alkaline, plants are unable to absorb the existing aluminum and the flowers will not blue. It is important when addressing the pH of your soil to remember that the ideal range of pH for the maximum absorption of nutrients is in the range of pH 6.0 to pH 7.0. It is within this limited range that we can in fact see the differing colors occur in hydrangeas.
It is more difficult to acidify soils than to make them more alkaline. The addition of lime to the soil will boost alkalinity, but increased acidity is achieved only by more laborious methods. The addition of acid organic matter like peat moss will gradually affect soil acidity, and the use of acid plant foods, those formulated for azaleas and rhododendrons will help. Some growers suggest using fertilizers in the form of nitrates rather than ammonium, and low in phosphorus, high in potassium. A soil test will save much trial and error, and achieving a pH of 7.0 to 7.5 will assure good pinks and reds, 5.5 to 6.5 being ideal for good blues, as long as a supply of aluminum exists as well.
For reasons that are not altogether understood, Hydrangeas will normally lose their ability to produce good blues when in their first year of growth, and when newly transplanted. Be patient; if you know your soil is acid and have supplied some supplemental aluminum they will turn blue, but it may take the better part of a year. Be sure to supply aluminum on an annual basis; for the best blues a twice-yearly feeding with aluminum sulfate dissolved in water and applied evenly over the roots is best. Aluminum can be reused by the plants but only if the flower heads are left until the following spring, when the element will be reabsorbed into the stems. When flowers art removed as fresh cut or dried specimens the aluminum will be taken away.
Hydrangeas are very sensitive to their immediate surroundings, particularly to soil. The root systems of the Macrophyllas and some Serratas are constructed like those of some spreading perennial plants such as Phlox; each stem will have a semi-independent set of roots which will absorb the available water, nutrients, aluminum etc., making the plant capable of producing some blue and some pink flowers if the acidity and aluminum are not evenly distributed. This sensitivity allows us to treat some plants to produce blue flowers, and others in the same bed to be red or pink. Those of you planning a red, white and blue border will be delighted to hear this.
Dried Flowers - Fresh Flowers; Cutting Hydrangea Blossoms
Dried Hydrangea blossoms have become very popular in recent years, and good flower heads of excellent color can fetch more than a dollar apiece on the wholesale market, often retailing for three dollars or more. While it is not easy to learn how to select the blooms at the right stage for drying, a little bit of trial and error will teach the willing learner in one season. Even the timid can succeed by simply being patient. Though some varieties never seem to produce good dried flower heads, most mopheads will dry many of their flowers naturally if the right conditions exist; a long season of gradual drying in air that is not to humid. These flowers will have changed considerably from their fresh color to shades of plum, mauve, steely blue, dusky rose, lilac, amber, tan, mahogany, brick red, sea green, parchment and other antique colors. These are sometimes known as 'antiques' in contrast with flowers that are cut while still fresh, and these antiques are already dry; just cut the flower head with a small bit of stem, remove any leaves and set in an empty vase to complete the drying process and keep their shape.
We can achieve a brighter range of colors by picking the flowers earlier in the season, but after they are ripe enough. When ripe they can be cut for use as fresh flowers with long stems, or with shorter stems to dry them thoroughly for later use in floral design.
When are they ripe? Mopheads are composed of many large flowers, sometimes referred to as 'sterile' florets. Within the large colored sepals lies a small round true flower which will eventually open, revealing the stamens and pistol. Until these true flowers have begun to open in good numbers, the flowers are too unripe to pick; their flowers will be relatively short-lived, surviving well for perhaps a week as a cut flower if carefully handled, but eventually wilting and never drying properly. But when many of the true flowers in an inflorescence have opened, the flower is ripe. We also try to gauge the ripeness by testing the feel of the sepals which should be starting to feel tough to the touch, not soft and moist.
Long stems can be taken for floral arrangements at this point. All leaves are stripped, the bottoms of the stems cut under luke-warm water, and the stems plunged up to the blossoms in water over night. It is helpful to finish by misting the flower heads so they will absorb more moisture. These stems if kept in water for two or three weeks will dry and can be saved for use as dried flowers. Another method employed is the cutting of just the flower head; this is often preferable if they are to be used solely as dried flowers, as less of the plant is removed, and the remaining stem can produce new blossoms later in the season or next year. These blossoms are not dried further in water but in the air, usually hung by their cut stem upside down, or laid in flexible netting in a cool dry environment with low light. Within a couple of weeks they will be fully dried and can be put to use.
Hydrangea Resources
An abundance of information can be found in the resources listed below. All of the books have been found for sale in recent searches on the world wide web. We are indebted to all of the authors listed below who have taught us much about this fascinating subject, but most of all to Corinne Mallet of France. Her two volumes, which are encyclopedic in their scope, have provided us with more clues to the identities of plants we have collected than any other single source. Mme. Mallet is a very astute and keen observer, and her comments on cultivars are accurate and revealing. We encourage all to seek out her books and buy them! Toni Lawson-Hall and Brian Rothera's book, published by Timber Press, is invaluable in its cataloguing of vital physical information on a large number of cultivars, in its detailed information on hydrangea species. These authors have thoughtfully included comparative analysis helping the reader to learn to distinguish between very similar cultivars. Their book is a must for all lovers of the genus Hydrangea. And, last, but never least, Michael Haworth-Booth in his seminal work from the fifties, The Hydrangeas, laid the groundwork for the revival of interest in this beautiful genus of plants. His perspective and his thoughtful observation of the plants continues to resonate today despite the contradicting conclusions arrived at by Dr. Elizabeth McClintock.