Hydrangea serrata Blue Deckle - Mountain Hydrangea

Hydrangea serrata 'Blue Deckle' is a heritage variety of mountain hydrangea with magnificent repeat flowering. Forming a compact, rounded shrub, it produces fairly dark green foliage that sets off the paler flowers. From June onwards, flat-topped inflorescences open in abundance. In acidic soil with a good supply of aluminium, they take on a superb, almost metallic light blue colour, while in neutral soil their colour ranges from pale pink to mauve pink. Flowering commonly repeats in late summer, and sometimes even in autumn, further enhancing this shrub's appeal. At the end of the season, its foliage also develops beautiful colours ranging from bronze to purplish red, before eventually falling to the ground. Suited to non-calcareous, humus-rich, moist soils, it thrives in light or even deeper shade in hot climates.

Hydrangeas belong to the Hydrangeaceae family, of which they form the principal genus. This family includes only 17 genera, among them the popular Philadelphus, commonly known as mock oranges, and the less well-known Carpenteria. The genus Hydrangea includes shrubs and climbing plants, generally deciduous, although some species, such as Hydrangea seemanii, retain their foliage all year round. Its name comes from the Greek words hydro, meaning "water", and aggeion, "vessel", referring to the shape of its fruits. Hydrangea serrata is a species closely related to H. macrophylla, from which the garden hydrangeas with large spherical inflorescences originate. However, it is hardier, thanks to its natural habitat. Native to the mountainous regions of Japan and Korea, where it can grow at altitudes of up to 1,500 metres, it tolerates temperatures of around -20 °C. This hydrangea forms a small shrub approximately 1.50 m in height and spread. Deciduous, it develops slender stems, often tinged with black, bearing foliage that disappears in winter.
Hydrangea serrata Blue Deckle was selected by British breeder Michael Haworth-Booth before 1950. The exact date on which it was introduced to the market, as well as its precise parentage, is unknown, although it is thought quite probably to be a hybrid between H. serrata and H. macrophylla. In any case, it received an award in spring 1992 at the Courson Plant Days, a major French event for plant enthusiasts and collectors. It develops into a densely vegetated shrub, with an irregular but more or less rounded habit, generally reaching 1.20 to 1.50 m in height and slightly more in width. If grown in a container, particularly because the soil in the garden is calcareous, its size will most often be limited to 1 m in height and spread. Its deciduous leaves are opposite and decussate (that is, positioned face to face and offset by 90° from the pair below). They are oval-lanceolate in shape, with a pointed (acuminate) tip and a finely toothed margin. Their colour ranges from medium to dark green depending on the aspect and soil, and they measure on average 10 cm long and 5 cm wide. In June, inflorescences approximately 10 cm in diameter appear. They consist of sterile flowers around the outside, reaching 2.5 to 3.5 cm in diameter, which surround much smaller fertile central flowers, only a few millimetres across. English gardeners call these inflorescences "lacecaps", because of their flat to slightly domed shape. The particularly generous main flowering is beautifully set off by the dark foliage, although it largely eclipses it, and lasts until July. In September and sometimes October, one or even two further flushes appear, extending the shrub's overall flowering period, much to everyone's delight. As with hydrangeas in general, the nature of the soil determines the colour of the flowers. In acidic soil with a good supply of aluminium, 'Blue Deckle', as its name suggests, turns blue: an original and remarkable light blue with metallic tones. If the soil is neutral (pH between 6.5 and 7), the inflorescences will be pink, ranging from pale pink to mauve. At the end of the season, shortly after the last flowers have faded, the foliage develops its autumn colours, generally an especially attractive purplish red.

Mountain hydrangea 'Blue Deckle' is a heritage variety that remains highly ornamental, offering a beautiful display in summer and autumn. Plant it in a bed alongside other ornamental plants that share its need for moisture and filtered light. Plant Andromeda polifolia 'Compacta' at its base, a low-growing variety of bog rosemary whose small white-pink bell-shaped flowers, appearing from April onwards, will precede those of your hydrangea. Mountain laurels will enliven the second half of spring with their highly original and extremely decorative flowers. To enjoy an immense choice of colours, also explore the range of dwarf rhododendrons, which will dazzle you in spring!