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Blue hydrangeas are a stunning addition to any garden, offering some deep, calming shades to any display. While you can buy ablue hydrangea plant as is, it's worth noting that you can manipulate the growth of certain species to bring blue into your outdoor space.
The colour of some hydrangea species, such as Hydrangea macrophylla and Hydrangea serrata, can be defined by soil pH and aluminium levels. This guide offers advice on how to keep the blue colour in hydrangeas, or bring it out of plants of different colours.
There are only twospecies of hydrangea that can change colour. Hydrangea macrophylla and Hydrangea serrata are the two kinds that you can manipulate the colour of. They’re known for taking on shades anywhere between deep purples and light pinks. Hydrangea paniculata and Hydrangea aborescens varieties will generally maintain a white, cream, light pink or very mild green colour, whatever the soil PH.
It might seem obvious, but choose a variety that has the word “blue” in its nickname if you’re looking for these flower shades.
Understandingsoil pH is vital to keeping a hydrangea plant blue. The key to this colour? Acidic soil. Blue hydrangeas can only grow in soil with a pH of 5.5 or lower, as this will allow the flowers to absorb enough aluminium (which is what actually turns them blue).
If you test your soil and the current pH isn’t suitable, such as being too high and alkaline, there are a few techniques you can use to manipulate it, such as:
Addingaluminium sulfate is a great, fast way to lower soil pH. It might need to be applied monthly during season to maximise the blue results.
Elemental sulfur can be added around the base of the plant for a more gradual shift in pH levels.
Acidic organic matter, like pine needles, old bark, dead leaves or coffee grounds can enrich the oil for a long-term shift in pH level.
Watering hydrangeas with rain water can also help to maintain acidity, with some tap water being too alkaline.
While it might sound acidic, Lime (calcium carbonate) will raise soil pH, rather than lowering it. Remember, none of these methods are overnighters – expect the change to take some time. Growing in containers might be the best way to control soil, so consider this against growing in borders or beds.
Once you’ve successfully shifted the colour in your hydrangeas, maintaining it takes consistent effort. Regularly check the soil pH and reapply your chosen acidifier, along with checking phosphorus levels. The latter can impact aluminium absorption levels, so use fertiliser with lower phosphorus levels.
Now that you’re confident about how to grow blue hydrangeas, you should seek them out from the best supplier possible – One Click Plants. We have plenty of blue and blue-readyhydrangeas available, along with aKnowledge Hub packed with information about all manner of plants and flowers so you can feel confident in the garden.
