How to prune Hydrangeas
Many amateur gardeners are unsure how to prune Hydrangeas, as there are different pruning rules for different species of Hydrangea. We explain what you need to look out for.
Hydrangeas are low maintenance and flower for a very long time – the wilted inflorescences are still very attractive. It’s no wonder that are one of the most popular garden plants and can be found in almost every garden. However, when it comes to pruning Hydrangeas, many amateur gardeners are unsure what to do and with good reason, because Hydrangeas are pruned differently depending on the species. If you prune them incorrectly, they may not flower the following year. The plants can be divided into two pruning groups.
- all Hydrangeas should be pruned by the end of February
- for your Bigleaf Hydrangea, only remove old blossoms and frozen branches
- always cut just above the first green pair of buds
- for smooth and Panicle Hydrangeas, trim the old flowering shoots back to one or two pairs of buds
- if the shrubs are very dense, completely remove individual old branches
All varieties of Bigleaf Hydrangea (Hydrangea macrophylla) and Mountain Hydrangea (Hydrangea serrata), as well as the large-leaved scabrous Hydrangea (Hydrangea aspera ‘Macrophylla’), the Sargent Hydrangea (Hydrangea sargentiana), the Oak-leaf Hydrangea (Hydrangea quercifolia) and Climbing Hydrangea (Hydrangea petiolaris) belong to Pruning Group 1. All of these Hydrangea species have one thing in common: next year’s new growth is created the year before, including the terminal buds. If you carefully open a Bigleaf Hydrangea bud in fall, you’ll already be able to see the new inflorescence and the new leaves inside.
This means that Hydrangeas in Pruning Group 1 only need to be lightly pruned to protect the new growth. In general, old inflorescences are cut back to just above the first healthy pair of buds and, if necessary, the entire plant is thinned out a little, by cutting off the oldest shoots at ground level. You can, of course, prune these Hydrangeas harder in spring, but you’ll then have to go without the beautiful flowers for a year.
The best time to trim Pruning Group 1 is in early spring. Most Hydrangea species in this Pruning Group are quite susceptible to frost. Therefore, remove any shoot tips, which have frozen in winter, along with the old inflorescences. Here too, you should cut all shoots back to the first healthy buds. Tip: if you’re not sure whether a shoot on your Hydrangea is frozen or still alive, simply use your thumbnail to scratch off a little of the bark. If bright green tissue appears, the shoot is still healthy. The bark tissue of dead shoots is usually quite dry and has a yellowish-green color.
The Hydrangea ’Endless Summer’ is very close to the classic Bigleaf Hydrangea botanically, but it has one special characteristic: heavily pruned flowering branches from the previous year sprout again, and, unlike normal Bigleaf Hydrangeas, will produce flowers the same year. You can therefore hard prune blue ‘Endless Summer’ and white ‘The Bride’, which come from the same breed, in spring if you need to. However, for these varieties, you should generally only remove dead flowers, otherwise the new blossoms will appear relatively late.
Tip: if you remove the first flowers in summer as soon as they have faded, the plants will form new flowers on the shoots. It therefore makes sense to grab your pruning shears every now and again in summer, just like with repeat-flowering Roses.
Pruning Group 2 includes all Hydrangeas which produce flower buds on new growth in the year of flowering. This is only the case for two species: the Smooth Hydrangea (Hydrangea arborescens) and the Panicle Hydrangea (Hydrangea paniculata), and includes all of their varieties. Hydrangeas in Pruning Group 2 are pruned like classic summer bloomers: in late fall or spring, simply cut back all shoots which emerged in the past season to short stumps with one pair of nodes. The remaining nodes will exhibit vigorous new growth and long, new shoots will emerge with terminal inflorescences.
With this pruning technique, the number of shoots doubles each year, as two new shoots emerge from each old one. If the crowns become too dense over time, you should completely remove weaker or awkwardly placed branches, or individual broom-like parts.
Important: do not cut these plants back too late, otherwise they will also flower relatively late. You should have pruned your plants by the end of February. They can be pruned much earlier in sheltered locations – for example, even in late fall – because the plants are more frost resistant than the hydrangeas in Pruning Group 1.
Hydrangeas are officially classified as mildly toxic and particularly sensitive people can suffer contact allergies in the form of skin irritation when maintaining the plant. If you know that your skin reacts sensitively when it comes into contact with plants, it’s better to wear gloves when maintaining Hydrangeas.