Hydrangea Colour Guide for South Africa: Blue, Pink & Purple Flowers

Few shrubs cause as much colour confusion as hydrangeas. One plant in your garden is bright pink, another is rich blue, and a third turns purple with age. What’s going on – and can you choose the colour you want?

This guide explains how soil pH, aluminium availability and variety affect hydrangea colour in South Africa, and how you can gently nudge your plants bluer or pinker over time.

Which hydrangeas change colour (and which don’t)?

Not all hydrangeas are colour-changers. The ones that shift between blue, pink and purple are usually:

• Hydrangea macrophylla – mophead and lacecap types (classic round or flat heads).

These are the hydrangeas most affected by soil conditions. In contrast:

• Hydrangea paniculata (panicle hydrangeas) usually open creamy white and age to lime, blush or soft pink. Their colour is mostly genetic and seasonal, not strongly pH-dependent.
• Many white-flowering hydrangeas stay white or only blush slightly and are less influenced by soil pH.

So if you want dramatic blue vs pink changes, focus on Hydrangea macrophylla types.

Blue vs pink: the simple rule

For Hydrangea macrophylla in suitable soils:

• Acidic soil (low pH) + available aluminium = blue tones.
• Neutral to alkaline soil (higher pH) = pink/red tones.
• In-between conditions often give mauve or purple.

It’s not just the pH – the presence of available aluminium in the soil is also important for strong blue shades.

South African soils and hydrangea colour

Many South African gardens have naturally slightly acidic to neutral soils, but it varies by region:

• Some Western Cape and forest-type soils tend towards acidic, especially under pines and oaks.
• Many suburban and older gardens have been limed or heavily composted over the years, which can push the pH more neutral.
• Areas with alkaline borehole water or lots of concrete/brick rubble can lean more alkaline near foundations and paths.

Because of this, the same variety planted in two different gardens – or even two different beds – can flower different colours.

How to encourage blue hydrangeas

If you’d like your macrophylla hydrangea to move towards blue or purple:

• Choose a variety that is known to blue well (many “blue” and “purple” named forms are selected for this).
• Plant in a large container or bed where you can control soil mix more easily.
• Use a potting or garden mix that is mildly acidic and low in lime.
• Feed with a fertiliser formulated for acid-loving plants (often sold for azaleas and camellias), following label rates.
• Ask your garden centre about a safe, garden-approved aluminium sulphate product for hydrangeas and follow instructions carefully.

Colour changes are gradual – you won’t see overnight blue from a pink plant, but over one or two seasons you can often see a clear shift in tone.

How to keep hydrangeas pink or red

If you prefer warm pink, rose or red tones:

• Choose naturally pink/red varieties, as they are more likely to hold their warm tones.
• Avoid frequent use of aluminium sulphate or acidifying fertilisers.
• In some cases, a light application of garden lime can help keep soil from becoming too acidic – always test and follow label rates.
• Use a balanced fertiliser rather than one specifically formulated for acid lovers.

Again, colour shifts slowly. A plant that has been very blue may soften through purple to pink over more than one season.

What about purple hydrangeas?

Purple or mauve hydrangea flowers often occur when:

• The soil pH is in-between – not strongly acidic, not strongly alkaline.
• You have a naturally pink variety in slightly acidic soil or a blue type in less acidic conditions.
• Blooms are ageing – many mopheads shift colour as they mature on the plant.

Some varieties are bred to show complex, two-tone or purple shades regardless of exact pH and will naturally sit in that colour range.

Important safety notes when adjusting soil

• Always use products labelled as suitable for garden use and follow the manufacturer’s instructions.
• Don’t overdo any one amendment – very rapid pH changes can stress plants and roots.
• If you’re unsure, work with containers where you can control the mix more easily and see how a single plant responds before treating the whole garden bed.

Beyond colour: choosing the right hydrangea

Colour is important, but so are plant size, sun tolerance and flowering habit. For a full overview of hydrangea types and where they thrive in South Africa, read:

• Hydrangeas in South Africa: Sun, Water & Pruning Guide
• Hydrangea macrophylla – Mophead & Lacecap Growing Guide
• Hydrangea paniculata – Panicle Hydrangea Guide

Then browse our Hydrangea collection to choose the right combination of colour, shape and size for your garden or patio.