Hydrangea macrophylla Gertrud Glahn

Hydrangea macrophylla 'Gertrud Glahn' is of German-origin with light pink to light blue flowering, depending on soil pH. It forms a rather compact bush, easy to integrate into a plant bed. Its numerous ball-shaped inflorescences are decorative throughout the summer. Resistant to cold, it should be planted in a semi-shaded position, in neutral to acidic soil. It is easy to cultivate, requiring only an annual pruning in spring and watering in summer to keep the soil moist.

Hydrangea macrophylla is a deciduous bush, native to Japan, where its beauty has been appreciated for centuries and mentioned in poems dating back to the 8th century! Festivals are even dedicated to this bush. It can be found in the wild on the island of Honshu (which is home to the capital Tokyo), and it was introduced to Europe around 1789.

'Gertrud Glahn' is a German variety selected by breeder Friedrich Matthes. Originally from Saxony (born in 1870 in Chemnitz), Matthes introduced new varieties of hydrangeas to the market from 1923 to 1934. His personal specifications were to offer floriferous varieties, with a compact habit, long-lasting flowering, and intense colours.

This is how 'Gertrud Glahn' appeared in 1934, a variety with light pink flowers in neutral soil, and light blue flowers in acidic soil (with lilac-blue nuances in intermediate soils). Compact as desired by its breeder, this small hydrangea measures from 1.2 to 1.5m (4 to 5ft) in all directions. Its growth rate is normal (15 to 50cm (6 to 20in) per year) and its medium to dark green foliage serves as a backdrop to its beautiful flowering. The large flower heads follow one another from June to September, making it one of the best summer-flowering shrubs.

It is not strictly an ericaceous plant, but prefers neutral to acidic soils. A semi-shaded to shaded exposure in warm climates will suit it well, as well as watering in summer, as it does not like drought (of the soil and atmosphere), which can cause its leaves to wilt. Care consists of an annual pruning in spring, before the new leaves emerge. This shrub is very hardy (-20°C (-4°F) or more, although severe frost can damage the tips of the branches. However, they easily regenerate after pruning in spring). Easy to cultivate, it can live for a very long time and adapts well to container gardening.

'Gertrud Glahn' is a good variety for growing in pots or containers, on a balcony or a sun-sheltered terrace in the afternoon. A thick terracotta pot would be well suited. If using a plastic container, choose one with a "double skin", meaning 2 walls separated by an air gap, forming an insulating layer, which prevents the potting soil from overheating and thus the roots in summer, and also slightly limits the effect of frost in winter. Use ericaceous compost adding a bit of compost. Regularly water in hot periods with non-calcareous water (rain water).

In the garden, plant it alongside spring-flowering shrubs so your garden will have flowers throughout the growing season. Choose compact plants to avoid suffocating it. For spring, Camellia japonica will be ideal. The lesser-known Magnolia 'Gold Star', with its yellow star-shaped flowers in April-May, will also be a very good companion for our small hydrangea.

Note: The colour of the flowers of macrophylla hydrangeas varies depending on the soil pH. Traditionally blue varieties turn pink in neutral or alkaline soil. To maintain a beautiful blue colour, mix ericaceous soil with your garden soil and apply aluminium sulphate (slate contains it) or alum stone every spring.