Hydrangea serrata Intermedia - Mountain Hydrangea

The Hydrangea serrata Intermedia (or Hydrangea serrata 'Acuminata') is a Japanese Hydrangea with changing colours throughout the season. Its flat inflorescences start off as a beautiful white in June-July, then turn pink before becoming red in the summer. Its deciduous dark green leaves turn bronze red in autumn. This small bush prefers cool, semi-shaded locations, in acidic to neutral soil, tolerating some limestone. Not exceeding 1.20 m (3 ft 11 in) in height, it can be grown in a container; in the ground, it will be perfect in a romantic or Japanese garden.

The Hydrangea serrata is a deciduous bush, native to the mountainous regions of Japan and Korea. It is sometimes considered a subspecies of H. macrophylla, with which it shares a number of characteristics, but it is more cold-resistant due to its mountainous origins, and also more compact in habit. Its flat-type flowers are also smaller, and like H. macrophylla, their colour varies depending on the soil pH. It grows in rich, moist soils, preferably in partial shade (tolerates sun if the soil is sufficiently moist). In winter dormancy, it can withstand -20°C (-4 °F), but the young shoots can be damaged by late frost.

The 'Intermedia' variety was obtained in 1950 in the United Kingdom by Michael Haworth-Booth. It is distinguished by the changing colour of its flowers and leaves throughout the season, making it a decorative plant for three-quarters of the year. The inflorescences, about 10 cm (3.9 in) in diameter, are of the "flat head" type, with small fertile flowers grouped in the center, and sterile florets on the periphery. The fertile flowers are blue in acidic soil, and pink in neutral to slightly alkaline soil. The florets, white when they emerge, become tinged with pink during the season and eventually turn red in summer. From June-July to August-September, it is a permanent festival of colours. The leaves are also beautiful, changing from dark green in spring and summer to more or less vivid bronze red in autumn, before they fall.

A plant for acidic soil (optimal pH 5 to 6.5), it also thrives in neutral to slightly alkaline ("limestone") conditions. It appreciates a few hours of morning sun and shade in the afternoon, and above all, a sufficiently moist soil, not liking drought. However, this Hydrangea does not tolerate excess water either, so the soil should be well-drained for it to thrive. In neutral or slightly alkaline soil, it will be important to add heath soil mixed with the existing soil. Then, it will only require an annual pruning in autumn to remove faded flowers. As the new flowers appear on the previous year's wood, pruning should be avoided, unless you want to encourage the emergence of new shoots by removing some old branches every other year.

A compact bush, about 1.20 m (3 ft 11 in) tall and 0.90 m (3 ft) wide, this Hydrangea can be grown in a container to enhance a shaded terrace. It will then need regular watering to prevent the substrate from drying out. Very hardy, it also tolerates sea wind and atmospheric pollution. Its natural appearance makes it suitable for use in a themed, wild, Japanese or romantic garden, alongside plants with simple charm. The arborescent peonies will be good companions, as well as a botanical Camellia like the Camellia transnokoensis with its moving spring flowering.