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Do Hydrangeas Need Ericaceous Soil? Only for Blue

Hydrangeas grow fine in ordinary soil. Ericaceous compost is about flower colour, not health — and only mophead and lacecap types change colour at all.

By Zakaria 2 min read Save to Pinterest — opens Pinterest in a new tab
Pink, mauve and blue mophead hydrangea flowers on the same planting
Photo: Bozhena, Pexels License, via Pexels
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No. Hydrangeas are not ericaceous plants — they grow perfectly well in ordinary soil. Ericaceous compost is about one thing only: getting blue flowers.

How the colour actually works

It is not the acid that makes the flower blue. It is aluminium, and pH only decides whether the plant can get at it.

Soil pH and what the flower does
Soil pHAluminiumFlower
Below 5.5AvailableBlue
5.5–6.5Partly availablePurple, or a muddled mix
Above 6.5Locked upPink

Which means two things people miss:

  • Acidifying a soil with no aluminium in it will not produce blue
  • A pot of ericaceous compost still needs aluminium sulphate to go properly blue

Which hydrangeas respond at all

Does pH change the colour?
TypeChanges colour
H. macrophylla — mophead, lacecapYes
H. serrata — some varietiesYes
White varieties of any typeNo, ever
H. paniculata — Limelight, Vanille FraiseNo
H. arborescens — AnnabelleNo
H. quercifolia — oakleafNo

A white hydrangea will never turn blue

No amount of sulphur, aluminium or ericaceous compost changes it. If that is what you want, the fix is a different plant, not a different soil.

If you do want blue

  • In a pot: ericaceous compost, plus aluminium sulphate to the label through the growing season. Much the easier option
  • In the ground: elemental sulphur worked in, over seasons rather than weeks, plus aluminium sulphate. On chalk, close to a losing battle
  • Rainwater, not tap water. Hard tap water is alkaline and will slowly undo the work in a pot
  • Keep it up. This is maintenance, not a one-off

Why a nursery plant turns pink: it was grown in treated compost, and your garden soil is not. Nothing has gone wrong.

What they actually need

The genus name comes from the Greek for water vessel, and that is the real requirement:

  • Moisture-retentive soil and a proper mulch
  • Morning sun, shade in the hottest part of the day
  • Shelter from wind
  • Water in dry spells — the commonest hydrangea problem by a wide margin is a wilting plant in dry soil, not a plant in the wrong pH

Common questions

Do hydrangeas need ericaceous soil?

No. Hydrangeas grow perfectly well in ordinary garden soil across a wide pH range, and ericaceous conditions are about flower colour rather than plant health. An acidic soil below about pH 5.5 frees up aluminium, which the plant takes up and which turns mophead and lacecap flowers blue. Above roughly pH 6.5 the aluminium is locked away and the same plant flowers pink. Neither is healthier.

Which hydrangeas change colour with soil pH?

Only Hydrangea macrophylla — the mopheads and lacecaps — and some Hydrangea serrata. White varieties do not change at all, whatever you do to the soil, and neither do paniculata types like Limelight or the oakleaf hydrangeas. If a white hydrangea is not turning blue, that is the variety, not your soil.

How do I make my hydrangea blue?

Lower the pH below about 5.5 and make sure aluminium is present. In practice that means ericaceous compost if it is in a pot, elemental sulphur worked in over time if it is in the ground, and aluminium sulphate applied according to the label through the growing season. It is slow, it has to be maintained, and it is far easier in a container than in an open bed, especially over chalk.

Why did my blue hydrangea turn pink?

The soil pH rose, or the aluminium ran out. Common causes are planting a nursery-grown blue plant, which was raised in treated compost, into ordinary garden soil; hard tap water, which is alkaline and gradually raises pH in pots; lime leaching out of nearby concrete or mortar; and simply not maintaining the sulphur or aluminium treatment. Pink is what the plant does by default in most garden soil.

Is ericaceous compost bad for hydrangeas?

Not at all — they grow happily in it, which is why nurseries use it. It is just unnecessary unless you want blue. One caveat: ericaceous mixes are lower in some nutrients and are designed for plants adapted to poor acidic ground, so a hydrangea grown in it long-term in a pot benefits from feeding through the season.

What do hydrangeas actually need?

Moisture and shelter, far more than pH. The name comes from the Greek for water vessel, and the commonest problem by a wide margin is a plant wilting in dry soil or in too much afternoon sun. Give them soil that holds moisture, a good mulch, morning sun with shade through the hottest part of the day, and shelter from wind — and the pH question stops mattering.

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