Hydrangeas: the flower of the Irish summer coast

Drive through Kerry or West Cork in August and hydrangeas are everywhere: great blue domes outside cottages, along hedges and in hotel gardens. Our mild, wet climate and acid soils suit them better than almost anywhere in Europe.

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Why the colour changes

The mophead and lacecap hydrangeas, Hydrangea macrophylla, act like a soil test. In acid ground, typical of much of the west and south-west, the roots can take up aluminium and the flowers turn blue. In limestone country, such as much of the midlands and the Burren, the same plant flowers pink. Neutral soils give in-between mauves and purples. White varieties do not change colour at all.

What hydrangeas mean

In flower language hydrangeas are given mixed messages, from heartfelt gratitude to coolness. Most people today see them simply as generous and abundant, a flower for a summer wedding, a thank-you to a host or a fourth wedding anniversary.

The main types

Mopheads and lacecaps (H. macrophylla): the seaside classics; mopheads have round heads, lacecaps a flat ring of open flowers around tiny fertile ones.
‘Annabelle’ (H. arborescens): huge white heads that fade to green; flowers on new growth, so it is easy to prune.
Panicle hydrangeas (H. paniculata): cone-shaped heads that open white and blush pink in autumn; very hardy.
Climbing hydrangea: self-clinging and happy on a shady north wall.

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Garden care in our climate

Prune mopheads in spring. Leave faded heads on all winter to shelter the buds, then cut back to a strong pair of buds once frosts ease.
Prune ‘Annabelle’ and panicle types hard in early spring. They flower on the new season’s shoots.
Water in dry spells. Even in Ireland, hydrangeas in pots or against walls dry out in summer.
Morning sun, afternoon shade keeps the colours rich, though in the mild west they take full sun too.

Cut hydrangeas at home

Recut the woody stem at a steep angle and put it straight into deep, cool water.
Strip most of the leaves; they draw water away from the flower head.
If a head flops, lay the whole thing under cool water in the sink for about half an hour.
Keep them out of warm rooms and draughts. A healthy head lasts around a week.
Late in the season, leave a few stems to dry in an empty vase; they keep their colour for months.

Hydrangea at a glance

Question	Answer
Botanical name	Hydrangea
In flower in Ireland	July to September
Blue flowers need	Acid soil
Pets	Toxic to cats and dogs

For other summer favourites see peonies and roses, or read about meanings in flower language.

⚠️ Toxic to pets: Hydrangeas contain cyanogenic glycosides. Cats and dogs that chew the flowers or leaves can suffer vomiting and diarrhoea. Keep cut stems and pot plants out of reach.

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Hydrangea questions

How do I make my hydrangea blue?

Blue needs acid soil, where the plant can take up aluminium. In lime-rich soil the same plant flowers pink. Growing in a pot of ericaceous compost and watering with rainwater helps, but white varieties stay white whatever you do.

When should I prune a mophead hydrangea in Ireland?

In spring, once the worst frosts are over. Leave the old flower heads on through winter, because they protect the new buds below, then cut each stem back to the first pair of fat, healthy buds.

Why does a cut hydrangea wilt so quickly?

The big heads lose water through the petals faster than the woody stems can draw it up. Recut the stem, remove most leaves and submerge the whole head in cool water for half an hour to revive it.

Are hydrangeas poisonous to pets?

Yes. Hydrangeas are listed as toxic to cats and dogs. Eating leaves or flowers can cause vomiting and diarrhoea, so keep cut stems and potted plants out of reach.