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Blue fertiliser for hydrangeas

Updated: October 2026

You searched for blue fertiliser for hydrangeas because a pink mophead, or a blue one that drifted pink on tap water, looks like a tub you can fix this weekend. Flower colour follows the cultivar and whether aluminium is available in acid soil. White, red and green flowers stay as they are, and some pinks are bred to stay pink. This page decides whether a pack is worth buying at all. Prices for the eight amazon.co.uk listings we kept on 19 October 2026 are in the [blue fertiliser comparison](/hub/fertiliser-soil-and-bark-mulch/blue-fertiliser). We used those listings, Royal Horticultural Society guides and the Westland label. We did not run a laboratory trial.

You searched for blue fertiliser for hydrangeas because a pink mophead, or a blue one that drifted pink on tap water, looks like a tub you can fix this weekend.

Our top picks

Topline Westland hydrangea feed and colourant bundle

Best overall

Topline Westland hydrangea feed and colourant bundle
6.8/10about £16.99
View offer
Vitax Vitax Hydrangea Feed, 1 kg, pack of 2

Preis-Tipp

Vitax Vitax Hydrangea Feed, 1 kg, pack of 2
8.2/10about £11.98
View offer
Westland Westland Hydrangea Colourant, 500 g

Rank 3

Westland Westland Hydrangea Colourant, 500 g
9.1/10about £6.99
View offer
On this page
  1. 1.Which hydrangeas a blue fertiliser can change
  2. 2.Colourant, feed, or a generic acidifier
  3. 3.What to read on the listing before you buy
  4. 4.What the packs cost on amazon.co.uk

Which hydrangeas a blue fertiliser can change

The Royal Horticultural Society limits the blue-pink shift to mophead and lacecap forms of Hydrangea macrophylla, to Hydrangea involucrata, and to Hydrangea serrata. Blue cultivars hold blue in acid soil around pH 4.5 to 5, because that is when roots can take up aluminium. A white mophead, a red cultivar, a green-flowered one, a panicle hydrangea and an Annabelle stay the colour they were bred. Some pink cultivars are also fixed. The plant label, or the nursery pot it came in, is the check before any basket. A colourant on a white shrub spends the summer doing nothing you can see. If the label says white, panicle, or a named pink that the breeder holds pink, leave the shelf.

Colourant, feed, or a generic acidifier

Three different products sit under searches for blue fertiliser. A colourant is a salt meant to change responsive pink flowers. A hydrangea feed is plant food for flowering. A generic acidifier may or may not name aluminium sulphate. Westland Hydrangea Colourant, 500 g, is the named colourant, at £6.99 with 4.2 out of 5 from 1,244 reviews. According to the manufacturer, on alkaline soil use ericaceous compost or double the stated rate. Vitax Hydrangea Feed, two 1 kg packs at £11.98, is sold with magnesium and iron. Aluminium is absent from the listing. Our Vitax row is the feed. Who should take which pack is on the best hydrangea colourant page. Generic packs around 109 to 119 g often have no review text. A missing analysis is a reason to prefer a named pack.
Topline Westland hydrangea feed and colourant bundle

Testsieger

Topline Westland hydrangea feed and colourant bundle
6.8/10about £16.99
View offer

What to read on the listing before you buy

An honest colourant page tells you the salt, the dose, the season, and the hazard. According to the manufacturer, work 50 g per square metre into the soil, then dissolve 50 g in 5 litres of water every seven days under the shrub, from April to September. The safety data sheet dated 8 January 2021 classes the powder as causing serious eye damage. Wear eye protection and keep it away from children. The weekly method is on how to use hydrangea colourant. 1,244 ratings outweigh a 5.0 from three silent ratings.

What the packs cost on amazon.co.uk

Prices here are the kept amazon.co.uk shelf prices on 19 October 2026. Generics run from about £3.49 to £6.26. The mid band is the Westland 500 g colourant at £6.99, and the Vitax feed at £11.98 for 2 kg. The upper figure is £16.99 for 1 litre of liquid feed plus the 500 g colourant, rated 4.5 from 74 reviews. From the weekly rate alone, 500 g is ten full 50 g drenches if you spill nothing. If the cultivar cannot change, none of these prices is a bargain. Compost versus a tub is on hydrangea colourant or ericaceous compost.

Common questions

Will blue fertiliser turn a white hydrangea blue?
No. The Royal Horticultural Society is clear that white, red and green cultivars stay as they are, and the Westland bullets in this set talk about pale pink to blue and dark pink to mauve blue. They do not claim a white flower. A panicle hydrangea or an Annabelle is in the same group. Check the plant label before you buy a colourant, a feed, or ericaceous compost for this purpose.
What is the difference between a colourant and hydrangea feed?
A colourant is sold to shift responsive pink flowers. In this set that is the Westland 500 g tub at £6.99. Hydrangea feed is sold to support flowering. The Vitax packs at £11.98 state magnesium and iron, and they do not state aluminium. Some Vitax reviewers still reported a blue or purple shift, so a feed can surprise you if you are protecting a pink you like. The two jobs can share a border. They are different tins.
Is a £3 aluminium sulfate tub the same as Westland?
The £3.49 listing names aluminium sulfate in the title and tells you to sprinkle 30 ml. It has no reviews, no percentage, and a title weight of 100 g against an item weight of 119 g. Westland is 500 g at £6.99, with 1,244 reviews and a manufacturer rate of 50 g. A shared salt name on a short title does not copy the dose, the hazard sheet, or the review history. Prefer the named pack when those lines are missing.
Can I use a colourant on chalk?
According to the manufacturer, the alkaline-soil line is ericaceous compost, or double the stated rate. Double means twice that printed figure, and you stop if the shrub declines. The Royal Horticultural Society warns that large or repeated aluminium sulphate doses can interfere with phosphorus. On chalk, a pot of ericaceous compost is the cleaner start. The double rate stays an alternative on that one label.
Is the Westland listing a liquid or a powder?
The amazon.co.uk item-form field says liquid. In the Amazon reviews, people describe a powder in a cardboard tube with a blue lid, sprinkled on the soil or dissolved in water. Open the parcel over a bin, because crushed tubes leak. Keep the drench on the soil under the shrub. White marks show up if the solution hits the leaves. According to the manufacturer, the season is April to September.

Related pages

Blue fertiliser comparison

Best hydrangea colourant

How to use hydrangea colourant

Colourant or ericaceous compost

Blue hydrangea in a pot UK: ericaceous compost first

Sources

Public UK and maker sources from the research digest, used for this page in October 2026. Prices, stars and review counts are the amazon.co.uk listings in that digest. The Westland dose and the 93% aluminium sulphate figure are from the manufacturer pages, not from the amazon bullets. A 5.0 from three ratings has no review text.

  1. RHS shrubby hydrangea growing guide (retrieved 22 October 2026)
  2. RHS acidifying soil (retrieved 22 October 2026)
  3. Westland Hydrangea Colourant (retrieved 22 October 2026)
  4. Westland safety data sheet, 8 January 2021 (retrieved 22 October 2026)
  5. BBC Gardeners' World, how to grow hydrangeas (retrieved 22 October 2026)
  6. Grow Scotland, hydrangea flower colour (retrieved 22 October 2026)
  7. Agriculture Act 1970, section 68 (retrieved 22 October 2026)
  8. Fertilisers Regulations 1991, Schedule 2 (retrieved 22 October 2026)