Should hydrangeas be pruned, and if so, how? Can we grow them in pots over several years? Why do their flowers turn pink when we wanted them to be blue? These three questions come up every year among gardeners. The answers actually depend on a few simple rules, often unknown, whether you are a beginner or an experienced gardener.
With their absolutely spectacular flowers, hydrangeas are fascinating plants that appeal to gardeners and nature lovers. But if their culture is not complex, certain questions come up regularly. It’s time to take stock.
Should you prune hydrangeas?
Yes, but… the size depends on the type of flowering of each species. Some, like the common hydrangea (Hydrangea macrophylla), flower on the previous year’s wood: pruning them therefore means removing the flower buds. For these varieties, it is better to avoid pruning and simply remove one branch out of four each year, cutting the oldest or least vigorous ones at the base.
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Other hydrangeas, on the other hand, flower on the year’s wood, such as the cultivar ‘Annabelle’ or the panicle hydrangeas. These can be pruned short at the end of winter without risk. Flowering will be later and the inflorescences less numerous, but they will in compensation be significantly larger, to the point of sometimes requiring staking.
Can you grow a hydrangea in a pot?
Growing hydrangeas in pots is entirely possible over several years, provided you choose compact varieties and ensure regular maintenance: watering, repotting or topping.
Among the varieties most suited to a 40 cm pot, we can cite ‘Tovelit’, very compact with its carmine pink flowers (60 x 60 cm), ‘King George’ in bright pink (80 x 80 cm), ‘Masja’ in bright red, or even ‘Merveille sanguine’ with blood-red flowers which blooms up to jellies. ‘Sunday Fraise’, little brother of the famous ‘Vanille Fraise’, and ‘Annabelle’, particularly resistant to drought, complete this selection.
Why don’t my hydrangeas stay blue?
The blue or purple color of hydrangeas does not depend on the gardener, but above all on the geology of the land. To turn blue, these plants need two simultaneous conditions: acidic soil (pH less than 6) and the presence of aluminum sulfate.
This is why hydrangeas naturally turn blue in Brittany, Normandy or the Basque Country, but remain pink in limestone regions like the Paris Basin. In calcareous soil, calcium blocks the absorption of alumina by the roots, and also deprives the plant of iron, causing yellowing of the leaves.
