When to prune hydrangeas?
- Botanical name
- Hydrangea macrophylla
- Family
- Hydrangeaceae
Hydrangeas are pruned in April. They are planted from September to May.
Hydrangeas are woody perennials.
The faded flower heads stay on the shrub through the whole winter. Under them sit the fat buds that the next flowering grows from, and a cut in autumn would remove them. The shrub is left uncovered over winter, and cold takes exactly those buds. The heads are cut later, down to the first strong pair of buds, and the oldest shoots are removed at ground level. Gloves go on for the work, because the plant is a skin allergen.
A hydrangea goes in partial shade, and it takes full sun only where the soil does not dry out in summer. Through the growing season it is watered whenever there has been no substantial rain for a while, and in the heat even a mature shrub needs water.
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Hydrangeas through the year
- pruning
- planting
In short
Growing conditions
Are hydrangeas toxic to cats and dogs?
Yes. Toxic to people and animals, toxic parts: bark, leaves and flowers.
Pests and diseases
Listed here is every problem for which the sources name this plant as a host. The problems are not listed in order of how common they are.
- Signs
- Colonies of small aphids sit on the shoot tips and the underside of the leaves. The leaf curls and puckers, and sticky honeydew is left on everything below. The viruses they carry are more dangerous than the feeding itself.
- Prevention
- Go easy on nitrogen, because soft sappy growth is what aphids are looking for. Encourage the predators (ladybirds, lacewings, parasitic wasps). Use a reflective mulch, which puts them off settling, and a strong jet of water to knock the colony off the tips.
- What to do
- Potassium soap works on contact and only while it is wet, so it has to reach the underside of the leaf. On drought-loving plants and in heat it can scorch, so apply it in the evening.
- Signs
- The plant dies suddenly, often in mid season and without any decline beforehand. Peel the bark at ground level and under it there is a white or cream sheet of fungal tissue, thin as the skin of a mushroom. In the soil there are black or brown strands like bootlaces. In late summer and autumn tufts of honey brown mushrooms with a whitish ring on the stalk appear by the stumps or over dead roots.
- Prevention
- The fungus spreads through the soil with its strands, from a few centimetres to a good hand's width below the surface, and infects the roots of a living plant when it touches them. So do not leave stumps and dead roots in the ground. No plant is completely resistant, but privet, lilac, viburnum, weigela, forsythia, butterfly bush, rhododendron, thuja and walnut are particularly susceptible.
- What to do
- There are no products. The only thing that works is digging out and removing every infected root and stump, which takes away the food without which the strands in the soil do not grow. A vertical barrier of rubber or thick plastic sheet, buried about half a metre deep and standing a few centimetres above ground, stops the spread into an unaffected part of the garden.
- Signs
- A white, floury coating spreads over the leaves, first on the lower and older ones. The leaf under it yellows and dries up. The fruit stays small, because the plant loses leaf surface.
- Prevention
- Plant resistant varieties, leave an airy spacing and sun, and clear the debris at the end of the season. Unlike most fungi it is not helped by wet foliage, since it spreads in heat and high air humidity, in a dry summer too.
- What to do
- Oil products meant for powdery mildew on the squash family work on contact. They do not cure a leaf that is already affected, but they stop the spread to healthy ones. On herbs cut the affected shoots back instead, since the new growth comes clean. On ornamental perennials what is left is spacing and moisture.
- Signs
- The half round notches along the leaf edges in summer are the work of the adult beetles and do the plant little harm. The larvae are the danger: white grubs with a brown head eat the roots, the plant suddenly drops its leaves and dies, most often between autumn and spring.
- Prevention
- Most at risk are plants in pots and troughs. In a bed the damage is rarer. At repotting check the roots and the compost and pick the larvae out. You find the adult beetles in the evening with a light, when they crawl over the plants.
- What to do
- Pick the adults off in the evening, set sticky traps indoors and change the compost, removing the larvae as you go. There is no insecticide. As biological protection, water beneficial nematodes into the compost at the end of summer, while the larvae are still small.
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Sources about the plant: GBIF Backbone Taxonomy, NC State Extension Plant Toolbox, Oregon State University, Royal Horticultural Society, Wikidata. Checked between 14 and 28 August 2026. The problem descriptions also draw on: Clemson Cooperative Extension, KGZS, UF/IFAS Extension, University of Illinois Extension, University of Maryland Extension, University of Wisconsin-Madison Division of Extension, Utah State University Extension.