The genus Hydrangea contains dozens of species and varieties, including deciduous shrubs and climbing plants. Most come from East Asia, some from America. Hydrangeas bloom from late spring until the end of summer. The flowers are clustered into corymbs or terminal panicles, and the colour of certain species is affected by the pH value of the soil, or more precisely by the minerals that it contains. One such element is aluminium, which gives them a blue coloration. If the soil is acidic—which hydrangeas prefer—the inflorescences will tend towards blue, whereas if it is alkaline the coloration will be pinkish.
The flowers that you probably most associate with hydrangeas are the spherical ones of Hydrangea macrophylla, the most common species, also known as Hydrangea ortensis. This is the species we will focus on in today's article about pruning hydrangeas.
When to prune hydrangeas
Pruning hydrangeas is a job that shouldn’t be neglected if you want luxuriant blooms, as it serves to stimulate the plants and keep them healthy. The optimal period for pruning is generally similar from one species to the next, but the technique varies according to the species because it is linked to the floriferous branches, i.e. the ones that produce flowers. Hydrangea macrophylla flowers first on one-year-old branches and then on young shoots developing from other younger or older branches.
But when should you prune hydrangeas? At the end of winter (latter half of February/March), once the new buds are clearly visible, temperatures are rising and there is no risk of damage due to cold or frost. Can you prune hydrangeas early, say in August? What you can do at the end of the flowering period, and before the leaves fall off, is trim the plants to remove any dead flowers.
So how should you prune hydrangeas? What you shouldn't do is indiscriminately shorten the tops of all the branches, as this would eliminate some of the best flower buds and compromise flowering potential. So let's look at the correct technique. In the meantime, for pruning hydrangeas in pots or in the garden, arm yourself with some well-sharpened pruning shears and a pair of utility gloves.
Pruning shears are not the only tool you can use for pruning. There are other manual tools (standard and telescopic), as well as power tools such as chainsaws and telescopic pruners. Depending on the type of work, you can use a hedgetrimmer (also available in telescopic hedgetrimmer versions) and, once you have mounted high-performance cutting line or blades or discs, a brushcutter.
How to prune hydrangeas
To prune hydrangeas, you should first remove withered flowers by cutting the stems above a pair of swollen buds, and remove older, exhausted branches by cutting them at the base. As a result, the hydrangea will have a less tangled appearance and you will be able to recognise more easily which branches to remove and which ones to leave.
The trick for pruning hydrangeas well is carefully selecting which branches to cut:
One-year-old branches: these flower first and within the next few months, so they should not be cut. They are long, vigorous and have no ramifications; they have brown or green bark and a large bud at the tip, which will produce the best inflorescences, i.e. larger and more colourful flowers.
Two-year-old branches or older branches, which are recognisable by their grey bark and withered flowers at the peak:
If they are exhausted, that is, if they have numerous weak twigs and no buds, cut them off at the base as we mentioned above.
If they have a young and vigorous lateral branch, then after cutting the dry flower, make a reduction cut that still leaves the branch on the plant (you can recognise a promising branch by the colour of the bark and the enlarged buds). There may even be multiple lateral branches with flowering potential: you can leave them all, pruning only withered inflorescences and the old part of the branch.
From what remains of the plant, cut off any branches that are thin, crooked, badly positioned etc.
Leave the green buds at the base of the plant: they will become branches in a year’s time, and flower for the first time in the following year. The result of pruning a hydrangea should be a well-pruned shrub where air and light penetrate freely, and which can concentrate its energy on the remaining branches and on flowering.
As for pruning other flowering shrubs like hydrangeas, here you will find an article on how to prune roses, which is another genus of plants that is very common in gardens. As for evergreen plants, click the link to find out how to choose, prune and tend them. Finally, here you will find a general guide to ornamental pruning.
Hydrangeas are acid-loving plants, so they prefer fertile and slightly acidic soil. What can you do about it? You can correct the pH of your flower bed by adding peat, or by spreading mulch made from plant material: learn more about how to acidify soil.
Why not demarcate your hydrangea bed by creating a border, which you could even combine with a do-it-yourself path? In these articles you will find various ideas for both projects. If you are looking for suggestions on remodelling or designing your garden, we offer you some advice to help you start off on the right foot.