Hydrangea serrata Summer Glow

Hydrangea serrata 'Summer Glow' is a variety of Hydrangea with flat heads that is particularly attractive, both for its flowering and its autumn colours. Depending on the acidity of the soil, its long-lasting summer flowering will display in blue or pink. The large inflorescences bloom above the dark green foliage, which highlights them particularly well. In autumn, the leaves turn a deep red, thus ending the season beautifully. With moderate growth, this bush is perfectly suited for small gardens, as well as container cultivation.

Hydrangeas are the most important genus in the Hydrangeaceae family, from which they get their name. This family includes only 17 genera, the most well-known besides Hydrangea being Deutzia and Philadelphus (Mock Orange). Hydrangeas include mostly deciduous species of shrubs and climbers, although there are a few evergreens, such as Hydrangea seemanii. The genus name comes from the Greek words hydro (water) and aggeion (vase), referring to the shape of the fruits.
Hydrangea serrata is a species closely related to H. macrophylla, the parent of our garden Hydrangeas with large spherical heads. However, it is known to be slightly hardier due to its geographical origin. It grows up to 1500 m in the mountains of Japan and Korea, which explains its hardiness down to approximately -20°C. This Hydrangea forms a small bush about 1.50 m in all directions, with deciduous leaves carried by thin, often blackish stems.
'Summer Glow' is a horticultural variety with a more compact growth, reaching a height of approximately 1.25 m at maturity with a spread of only 1 m. The bush forms a dense clump, which is well-suited for low hedges. The leaves are opposite, lanceolate to elliptical, measuring from 5 to 15 cm in length. The edge of the leaf blade is slightly toothed, and its colour is a fairly dark green, with a well-marked central vein, slightly lighter green. The flowers appear on one-year-old wood, from June to August. The inflorescences are composed of small fertile flowers in the centre, surrounded by sterile ray florets on the periphery. As with most species, the colour of the flowers depends on the pH of the soil, which affects the assimilation of aluminium. In acidic soil, aluminium is available and causes the desired blue colouration. In neutral soil, on the other hand, this element is much less assimilable, and the flowers turn pink. The choice is irrelevant in limestone soil, as then the entire plant suffers from chlorosis and yellows. The inflorescences, with a diameter of more or less 14 cm, rise slightly above the mass of foliage, making them very visible, especially as the darker background of the vegetation serves as a true showcase. This long-lasting flowering is extremely decorative during the summer. When the first cold nights of autumn arrive, the foliage evolves and gradually turns a deep red, creating a beautiful effect.

With good hardiness and compactness that allows for container cultivation, 'Summer Glow' Hydrangea appreciates moist soils and bright positions, protected from direct sunlight, especially in hot climates. It will be more comfortable under the protective shade of large shrubs in the south, which will also maintain a certain atmospheric humidity. Combine it in a border bed with other shrubs that flower at different times to create an ornamental scene throughout the seasons. Corylopsis pauciflora, or Buttercup Winter Hazel, will reward you with its fragrant yellow flowers in March and April. It will be followed by the magnificent Magnolia denudata 'Iolanthe', which blooms with its huge pink flowers, reaching 25 to 35 cm, in April and May. One or two Rhododendron (or Azaleas) will take over and ensure a smooth transition with your Hydrangea. And to complete the circle, nothing beats an Autumn Camellia (Camellia sasanqua) to provide you with a sculptural, colourful flowering during the end of the year.