The popular and easy-care hydrangeas are true long-flowering plants and are still attractive to look at in the garden even when they have wilted. With the right care and choice, they will enchant your balcony, garden or terrace all summer long. We outline how to prune hydrangeas and – importantly – when to prune hydrangeas in each of the 2 main categories.
- How to prune hydrangeas: overview
- How to prune hydrangeas: category 1
- How to prune hydrangeas: category 2
- No rule without exception
- What to watch out for
- Warning about drug experiments
- How to change hydrangea color
How to prune hydrangeas: overview
Many gardeners are unsure when prune hydrangeas at first, as different cutting rules apply to the different types of hydrangea. In principle, every hydrangea can be pruned heavily. However, incorrect pruning and timing can result in no or few flowers being produced when how to prune hydrangeas is not properly understood. Follow our guide to understand what to do and when.
There are some species that can easily tolerate a strong pruning and even reward them with magnificent flowers in the following year. But most hydrangeas only prefer very light pruning measures, as they set their flower buds on the shoots in the previous year. If the shoots were to fall victim to the scissors, the flowers would not appear. Also read how to prune apple trees correctly.
Hydrangeas can be divided into two categories with regard to the correct pruning technique.
How to prune hydrangeas: category 1
This category covers the many hydrangea species, including the well-known farmer’s hydrangea, that set their flowers in the previous year — these shoots can already be seen well in winter.
The plants of category 1 include all varieties of the farmer’s hydrangea (Hydrangea macrophylla) and the plate hydrangea (Hydrangea serrata) as well as the giant leaf hydrangea (Hydrangea aspera ‘Macrophylla’), the velvet hydrangea (Hydrangea sargentiana), the oak leaf – Hydrangea (Hydrangea quercifolia) and the climbing hydrangea (Hydrangea petiolaris).
All of these hydrangea species have one thing in common: they create the new shoot for the next year, including the terminal flower buds, in the previous year. If you carefully open a bud of the farmer’s hydrangea in autumn, you can already see the new inflorescence and the new leaves.
This means that the hydrangeas of cutting group 1 are only slightly cut back in order to protect the new shoot. As a rule, the old inflorescence is removed just above the first intact pair of buds and the entire plant is thinned out a little if necessary by cutting off the oldest shoots at ground level. You can of course prune the hydrangeas mentioned above more in the spring, but then you will have to do without the beautiful flowers for a year.
When to prune hydrangeas: category 1
The best time to cut the hydrangeas of cutting group 1 – depending on the weather – is early spring, i.e. the end of February or March. If the plant is older and has lost its flowering power, some older shoots can also be cut off near the ground. If an older hydrangea is to be rejuvenated, it is worth radical pruning to a hand’s breadth above the ground. Also read when and how to prune roses correctly.
The reason to prune hydrangeas in spring in this category is that most of the hydrangea species in this group are somewhat sensitive to frost. Therefore, with the old inflorescences, remove all shoot tips that have frozen in winter, but you should not fully prune hydrangeas in winter.
Here, too, you should cut off all shoots at the level of the first healthy buds. Tip: If you are not sure whether a shoot of your hydrangea is frozen to death or is still alive, you should simply scrape a little off the bark with your thumbnail. If bright green tissue appears underneath, then the shoot is still intact. The bark tissue of dead shoots is usually already somewhat dried out and has a yellow-green hue.
Special case hydrangea ‘Endless Summer’
From a purely botanical point of view, the hydrangea ‘Endless Summer’ is very close to the classic farmer’s hydrangeas, but has a special property: Heavily cut back flowering branches from the previous year sprout again and, in contrast to normal farmer’s hydrangeas, bear flowers in the same year. Therefore, you can prune back the blue ‘Endless Summer’ and the white ‘ The Bride’, which comes from the same breeding line, as much as you want in the spring. Basically, you should only remove the faded inflorescences from these varieties, otherwise the new flowering will start relatively late.
Tip: If you see the first flowers in summer immediately after the hydrangea has fadedremove, the plants will form new flowers on the shoots. Therefore, as with the more frequently blooming roses , it is worthwhile to use secateurs every now and then in summer.
Quick guide: how to prune hydrangeas in category 1
- The rule: Prune hydrangeas spring, cut dead blossoms autumn. Ideally, dried out blossoms should be cut back in autumn, but pruning in spring is also possible. It is important to make the cut just below the inflorescence so as not to endanger the flowering in the following year.
- Cut out weak and dead branches: Together with cutting off the inflorescences, sick and weak shoots can also be cut out. This lowers the risk of infection with fungal pathogens and creates some light inside the woody bush.
- Remove old shoots: Older shoots that are already very branched and have very strong branches at the base should be removed at times. Depending on the size and age of the hydrangea, more or fewer shoots can be cut a few centimeters above the ground. This gives the plant more energy for the new shoot and larger flowers on the younger, more vital branches.
- Avoid radical pruning! Hydrangeas that only tolerate light pruning are:
- Farm hydrangeas
- Giant Leaf Hydrangeas
- Plate hydrangeas
- Velvet hydrangeas
- Oak leaf hydrangeas
- Climbing hydrangeas
How to prune hydrangeas: category 2
In group 2, all hydrangeas are included that only form their flower buds on the new shoot in the year of flowering. This includes only two types: the snowball hydrangea (Hydrangea arborescens) and the panicle hydrangea (Hydrangea paniculata), each including all varieties, so the instructions below will work for them — for how to prune hydrangea limelight, for example, which is a paniculata.
Hydrangeas of cutting group 2 are cut like classic summer bloomers: In late autumn or spring, simply prune all the shoots that have emerged in the previous season to short stubs, each with one pair of eyes. In the coming season, the remaining eyes will sprout vigorously and long new shoots with large flowers will appear.
In the case of the snowball hydrangea and panicle hydrangea, all shoots except for short stubs are cut back in early spring or in late autumn
With this pruning technique, the number of shoots doubles year after year, as two new shoots are created from each old shoot. If the crowns become too dense over time, you should therefore completely remove weaker or poorly placed shoots or individual “twig brooms”. Also read how to prune fruit trees correctly.
Important: Do not cut back these plants too late, otherwise flowering will also start relatively late. You should have cut the trees by the end of February . In protected locations, it is also possible to cut much earlier – for example in late autumn – because the plants are more frost-resistant than hydrangeas in cutting group 1.
Hydrangeas that can tolerate more pruning:
- Paniculata hydrangeas
- Snowball hydrangeas
No rule without exception
The modern cultivars of the farmer’s hydrangea (Endless-Summer, Forever & Ever, Everblooms) bloom as well as the hydrangea species of cut group 2 on the new wood. However, these varieties are only cut approx. 20-30 cm above the ground after the main flowering. A pruning is even essential here, as these special species do not have a permanently compact growth and would fall apart without the right pruning measures.
How to prune hydrangeas: climbing hydrangeas
Actually, a climbing hydrangea ( Hydrangea petiolaris ) doesn’t really need pruning. However, the previous year’s flowers should also be removed here. On the one hand, it looks nicer and also protects against fungal attack. However, should the climbing hydrangea grow over your head, it can be cut back without any problems. However, it should be noted that flowering will probably not occur, as Hydrangea petilolaris, just like farm hydrangeas, blooms on perennial wood. More information on cutting climbing hydrangeas can be found here.
Most climbing hydrangeas turn their leaves yellow in autumn and then lose them. However, some new varieties keep their green leaves even in the cold months, for example Semiola . This hydrangea also has copper-red shoots in spring. An evergreen alternative is the climbing hydrangea of the Silver Lining variety with white borders around the leaves. According to the Association of German Tree Nurseries, it is ideal for containers on balconies and patios.
What to watch out for
Hydrangeas are officially considered to be slightly poisonousand particularly sensitive people may experience contact allergies in the form of skin irritation during care work. If you know that your skin is sensitive to contact with plants, it is better to wear gloves when caring for hydrangeas.
Warning about drug experiments
In recent years it has been reported that the cannabis scene is targeting the hydrangea as a homemade drug substitute. Police authorities reported increasing thefts of hydrangeas. If the ornamental plants are burned or smoked, hydrogen cyanide is released. However, experts warn against inhaling the smoke, as this leads to poisoning. The possible consequences range from loss of consciousness and disorders of the nervous system to death. When consumed raw, the plant, like most, only causes stomach problems and nausea.
How to change hydrangea color
If you have hydrangeas in your garden, you may have noticed that the color of the hydrangea suddenly changes in the year after purchase. So it is quite possible to buy a blue-flowered hydrangea and the following year it will flower pink. But where does it come from and how can you change the color of hydrangeas?
The soil or the pH value of the soil is how to change hydrangeas colors: the more acidic the soil, i.e. the lower the pH value, the more blue the plant will bloom. Garden soil usually has a pH value of six to seven. However, a pH value of around five would be ideal.
Lower the pH value with fertilizer
In order to lower this, one can either fall back on special soil or use fertilizer. The soil is bog soil, which lowers the pH value and thus returns the blue color to the plant. If you do not want to replace the entire soil, you can help with fertilizer. This either has to contain a lot of aluminum sulfate or you choose one with a lot of potassium, but with little phosphorus. And the flowers will turn blue again!