Hydrangeas Revised Edition: A Gardener's Guide - Tapa dura

Most hydrangeas are natural woodland plants, yet this is not always taken into consideration when choosing a site. The high cover of tall woodland trees gives dappled shade which is ideal. In such a setting the hydrangeas flower well, but the blooms are protected from strong sunlight. While early-morning and late-afternoon sun do no harm, hours of midday sun can bleach the flowers and finally scorch them, so that they turn an unattractive brown colour. Shrubs grown in a woodland site not only keep their flowers well and true to colour, but the colours seem almost luminescent in the semi-shade. Moreover, both flowers and leaves last longer into the winter when under some tree cover, and can still be seen shining out on a dull winter day. Edge of woodland, too, is ideal especially if some evergreens are included, as the trees give not only shade and protection but also a backcloth for the various coloured blooms.

Aspect is not a simple subject, however. Dappled shade, which undeniably suits hydrangeas, is not always easy to achieve. A tree canopy which produces dense shade will also prevent sufficient precipitation from reaching the shrubs below. They will then fail to thrive because of the shortage of moisture, light and food, and smaller flowers on a small, starved bush will result. Too much sun also can he damaging, but even here one cannot generalize, for in northern England and Scotland, the fewer hours of sunshine and the lower angle of the sun will allow greater exposure without the flowers spoiling. All these factors need to be taken into consideration.

As well as assessing the balance of sun and shade, care should also he given to the individual plant's habits; not all hydrangeas react to the elements in the same way. Cultivars of H. aspera, for example, prefer some tree cover, while cultivars of H. paniculata, whose brittle stems are at risk in strong winds, nevertheless flourish in full sun. H. arborescens cultivars are hardy and withstand cold, heat and drought better than other species, while H. quercifolia likes warmth. Cultivars of H. macrophylla ssp. serrata, most of which originate in the mountains of Japan, prefer some shade, or a cool temperate climate, given which they are very robust.

The numerous cultivars of H. macrophylla (the familiar mopheads and lacecaps) show many variations in their response to sun. On the whole, the lacecaps withstand hot sun better than hortensias, although their colours are less intense. H. m. 'Lanarth White', for example, a lovely white lacecap, fares well in an open position, and does not readily scorch. The white mopheads, however, require some shade to protect them. H. m. 'Mme E. Mouillère', an old-established white mophead but still one of the best, gives a splendid display all summer if grown against a north-facing wall. Those hortensias that come into flower early, blooming in June and July, are subjected to the sun at its highest, and are more readily scorched. Later flowerers, and occasional autumn blooms, developing when the sun-power is less, can provide a freshness of colour which prolongs the season. Blue hortensias seem to suffer more conspicuously from scorching than pink or red ones, hut such a generalization is risky. H. m. 'Gentian Dome' resists scorching better than H. m. 'Maréchal Foch', both excellent deep blues, on soil of pH 6.5 or less. Mention of other responses will be found under the individual plant descriptions.

Proximity to the sea means greater humidity, which reduces the damaging effects of the sun. Mopheads and lacecaps flourish in these conditions, for they are naturally littoral plants. In Britain, where the warming effect of the Gulf Stream is felt on the western shores, superb hydrangeas can be seen as far north as the Isle of Skye. Some compensation, then, for living where cloud and mist is common — hydrangeas will flourish! Among plants which particularly benefit from these conditions are H. m. 'Sea Foam', 'Joseph Banks' and 'Ayesha'. Britain's north-east coasts are subject to cold winds, and are thus less hospitable to hydrangeas.

Not all of us, however, live near the sea, nor do we have areas of woodland, so how can we best satisfy the hydrangea's need for shelter? Most gardens have some shade, and, in more northerly latitudes, it is only the hottest midday sun from which protection is needed. A wall, fence or hedge may be the answer, with a north-, east- or west-facing bed being preferable to a south-facing one. The shadow of one large tree may be all that is needed to cut out the hottest sun — sometimes, a neighbour's tree does just that. The foot of a house wall, facing north, east or west is traditionally a good place for hydrangeas, provided that care is taken with soil preparation, feeding and watering. Evergreen shrubs can give excellent protection, as well as providing a pleasing backcloth to the hydrangeas. Some evergreens, such as rhododendrons and pieris, have similar requirements to hydrangeas and complement them by flowering at a different season. In alkaline soils, varieties of holly, mahonia and eleagnus, to quote but a few, would make good companions and provide the necessary shelter.

The majority of hydrangeas flower on the wood produced during the previous year. Flower buds are carried through the winter and will begin to develop, often rather too early, in the spring, ready for flowering in later summer and autumn. They are at their most tender in April and May and can be completely destroyed by searing cold winds. More flower buds can he formed later in the year, hut these will not be ready to produce blooms in the same season. So, although the plant will not die — it takes a lot to kill a hydrangea — a whole season's flowers can be lost.

The winds most likely to create this sad cycle of events come from the north and east in the British Isles, so it is from these directions that some protection should be given, if possible, when considering planting positions. Very strong warm winds from the south and west, while they may snap off a few flower heads, do not cause shrivelling of the buds and leaves — the hurricanes in Britain of autumn 1987 and spring 1990, which felled so many trees, had little effect on hydrangeas. Hydrangeas will grow on the western side of the British Isles with less protection than they would need on the east. Should winds pose such a problem that shelter does have to be provided, this is best done by trees, hedges or evergreen shrubs — or failing these, by a latticed fence. Any of these will filter the wind and reduce its speed, whereas walls or solid fences can create turbulence without lowering wind velocity.