Bigleaf hydrangea: pruning, feeding, flower colour and overwintering

Why bigleaf hydrangea does not flower after pruning, how flower colour changes through soil pH, a feeding calendar and what to do with the shrub in autumn and winter.

In brief: Bigleaf hydrangea wants partial shade, moist acid soil and plenty of water. Feed it from April to the end of July with a fertiliser for acid-loving plants. Do not prune it in autumn: the buds for next year are already sitting on the ends of last year's shoots. It is poisonous to dogs, cats and horses.

Latin name	Hydrangea macrophylla, Hydrangeaceae
Height	usually 1–2 m, in a container 0.5–1 m
Position	partial shade, morning sun, no midday scorching
Soil	acid and moist; blue colour holds at roughly pH 4.5–5.5
Feeding	April to the end of July, then stop
Pruning	early spring, spent flower heads back to the first pair of strong buds

Bigleaf hydrangea is a shrub with large round or flat flower heads in blue, pink, violet or white. In the garden it flowers from June to September, and many people bring it home from a florist as a potted plant that they then want to keep for further years.

Most problems with it have three causes: drought, poor soil and pruning at the wrong time. Below you will find how to deal with them, how to influence flower colour and what to do now in autumn so that the shrub flowers next summer.

Mophead or lacecap: which hydrangea you have

Under the name bigleaf hydrangea two flower shapes are sold. Round heads made up only of large sterile flowers belong to hydrangeas called "mophead" in garden centres. Flat plates, where tiny fertile flowers sit in the middle and a ring of large ones around the edge, are the so-called "lacecap". The care is the same for both; lacecaps are usually somewhat hardier against frost.

A different distinction is more important. Classic varieties set their buds on last year's shoots, that is already in August and September. Newer remontant varieties (sold, for example, under the name Endless Summer) also flower on this year's shoots, so they flower even if the buds freeze in winter. If you do not have the label, assume that your hydrangea flowers on old wood.

Do not confuse bigleaf hydrangea with panicled and smooth hydrangea. Those flower on this year's shoots, tolerate full sun and hard spring pruning and are not troubled by frost in winter. The pruning advice in this article does not apply to them.

Position and soil

It does best in partial shade with morning sun, for example by an east-facing wall of the house or under the light crown of a tree. In full midday sun the leaves wilt in summer even with watering, and in deep shade it flowers little. Avoid places where cold wind blows and frost pockets where sprouting buds freeze in spring.

The soil should be humus-rich, constantly slightly moist and acid. In ordinary garden loam with a neutral or alkaline reaction hydrangea grows, but the flowers turn pink and the leaves may yellow. How to measure soil reaction and what influences it is explained in the article soil pH.

Planting step by step

Plant in spring after the last frosts or early in autumn, by the end of September, so that the shrub manages to root.
Dig a hole twice as wide as the root ball and as deep.
Mix the excavated soil half and half with compost or substrate for acid-loving plants.
Before planting, soak the ball in water until bubbles stop rising from it.
Plant the shrub to the same depth as it grew in the pot and water thoroughly.
Mulch the surface with a 5–7 cm layer of bark or leaves, which holds moisture and acidifies slightly.

Why mulch helps especially with moisture-loving shrubs is discussed in the article why mulch a bed.

Blue or pink? Colour by pH

In blue and pink varieties, the soil decides the colour. The blue pigment forms only when the plant takes up aluminium, which is available in acid soil. As long ago as 1846 J. S. Presl wrote that ochre is mixed into the soil for blue flowers. White varieties do not change colour.

Soil reaction	Colour of coloured varieties	What to do
pH about 4.5–5.5	blue	keep the soil acid, water with rainwater
pH about 5.5–6.5	violet, mixed shades	for blue add aluminium sulphate, for pink lime
pH above 6.5	pink to red	you cannot keep blue in the long term, plant pink varieties

Turning flowers blue is a long-distance race. Aluminium sulphate is given from spring in several doses according to the instructions on the packaging, and the change shows only in later flowers, often only next year. Hard tap water with calcium gradually raises the pH, so water blue hydrangeas with rainwater. Fertilisers with a high phosphorus content bind aluminium in the soil; for blue shrubs choose a fertiliser for rhododendrons and hydrangeas.

In a container the colour change is easier because you control the substrate. All you need is to plant in a substrate for acid-loving plants and water with soft water.

Feeding through the year

Period	What to do
April	first dose of fertiliser for acid-loving plants, top up the mulch
May–July	feed according to the instructions, with granules usually once every 4–6 weeks, with liquids more often
from August	do not feed, the shoots must ripen and set buds
autumn and winter	just mulch and protection from frost

Late feeding with nitrogen is a common mistake. The shrub then pushes soft shoots in autumn which freeze in winter together with the buds. General principles for choosing fertilisers can be found in the article how to choose a fertiliser.

Watering: hydrangea does not tolerate drying out

The Latin name Hydrangea refers to water, and it is no coincidence. The large leaves lose a lot of water and on a hot day wilt even in slightly moist soil. If they perk up again in the evening, it is a normal reaction to heat. If they are wilted in the morning, the shrub is thirsty.

In summer water generously in the morning, rather properly twice a week than a little every day. A shrub in a container may need water every day in July. Water in the saucer must not stand for long, however, or the roots rot. How to prepare a container so that excess water drains away is described in the article drainage in a flower pot.

Pruning: why hydrangea does not flower after cutting

Bigleaf hydrangea has ready-made buds on the ends of last year's shoots. Anyone who shortens it "to shape" in autumn or in spring cuts off this year's flowers. The right method is gentle:

Leave the spent flower heads on the shrub over winter. They protect the buds beneath from frost and look good in hoar frost.
Wait until the end of March or April, until the buds swell and you can see which have survived.
Cut each dry head just above the first pair of strong, healthy buds beneath it.
Remove dry and frost-damaged shoot ends back to healthy wood.
On older shrubs cut out one or two of the oldest shoots at ground level. This gradually rejuvenates the shrub.

Radical rejuvenation of all shoots to the ground is possible, but the shrub will not flower that year.

Other reasons why it does not flower

Frozen buds. A late spring frost scorches the sprouting shoot ends. The shrub sprouts again, but without flowers.
Too much shade. In deep shade it forms leaves and few flowers.
Nitrogen at the end of summer. Soft shoots do not manage to ripen and set buds.
Drought in August and September. That is when the buds for next year form.

What to do now in autumn and in winter

The end of September is the last sensible date for planting. After that just water while it is dry and leave the shrub in peace. After the first frosts, pile a layer of leaves or bark around the base of the shrub. In colder areas and in hard frosts without snow, throw white non-woven fleece over the shrub; in spring keep it handy for nights with light frost, when sprouting buds suffer most. General advice on autumn preparation can be found in the article important advice for winterising the garden.

A hydrangea in a container freezes through the whole root ball, so move it for winter to a cool frost-free room, for example a garage or cellar at a temperature up to 8 °C. After leaf fall darkness does not harm it either. Do not let the substrate dry out completely; water roughly once every two to three weeks.

Hydrangea from a florist

A potted hydrangea bought in spring was forced in the nursery. After flowering repot it into a larger pot, put it outdoors after the last frosts and in later years grow it like a garden shrub. In the first year after purchase the flowering is usually weaker.

Is hydrangea poisonous?

Yes. Hydrangea contains cyanogenic glycosides. The American ASPCA lists it as poisonous to dogs, cats and horses. After chewing, vomiting, diarrhoea and lethargy mainly appear. According to the ASPCA cyanide poisoning is rare; it is usually digestive upset.

The same applies to small children: leaves and flowers do not belong in the mouth or in children's "cooking". If you suspect poisoning of a child, call the Toxicological Information Centre on 224 919 293 or 224 915 402, and for an animal a vet.

Frequently asked questions

When should I prune bigleaf hydrangea?

Early in spring, from the end of March to April, when the swollen buds are visible. Shorten spent heads to the first pair of strong buds. Do not prune it in autumn, as you would cut off the buds for next year.

How do I make a hydrangea blue?

You need acid soil, roughly pH 4.5–5.5, and available aluminium. Aluminium sulphate, a substrate for acid-loving plants and watering with rainwater help. White varieties do not change colour, and in alkaline soil you cannot keep blue in the long term.

Why does my hydrangea not flower?

Most often because of pruning at the wrong time, frozen buds or deep shade. Drought and feeding with nitrogen in August, when the shrub is setting buds for next year, also play a part.

What should I feed hydrangea with?

With a fertiliser for rhododendrons, azaleas and hydrangeas, which maintains an acid reaction. Feed from April to the end of July and stop from August.

Can a hydrangea in a pot stay outdoors over winter?

Only in a mild winter and in a sheltered corner with the pot wrapped. It is safer to overwinter it in a cool frost-free room up to 8 °C and water it occasionally.

Is hydrangea poisonous to cats and dogs?

Yes, it contains cyanogenic glycosides. Most often it causes vomiting and diarrhoea. If you suspect an animal has chewed the plant, contact a vet.

Sources

Updated: 27 September 2026

Author: Jana Vránová, the editorial name of the Pěstík.cz team. She writes about the garden, herbs and essential oils. We take safety and dosage information from specialist literature and official sources, which we cite in every article.