Did you know you can change the colour of hydrangeas? Well, at least when it comes to mophead and lacecap cultivars of Hydrangea macrophylla, Hydrangea involucrata, and Hydrangea serrata. Maybe you want to try a new look for your shrubs. Or, perhaps you've noticed your once-blue bloomer turning pink unexpectedly and want to get it back to its former hue. Either way, the process is quite straightforward once you know how.
These plants are one of our favourite flowering shrubs for adding structure and vibrancy to a plot. What's more, learning how to grow hydrangeas is easy, so they're ideal for novice and experienced gardeners alike.
And they're not just for borders – you can plant them in containers too. In fact, changing the colour of hydrangeas in containers is easier than those planted straight into the ground as you have more control over the soil. We explain everything you need to know in this simple guide.
How the soil pH impacts the colour of your hydrangeas
Hydrangeas with blue or pink flowers tend to be blue in acid soil conditions, mauve in acid to neutral soil conditions, and pink in alkaline conditions.
This means that by changing the pH of the soil, you can achieve different hydrangea colours to complement your garden colour scheme. Bear in mind that the colour change won't happen overnight, however – it is an ongoing process.
How do you make your hydrangea blue?
Whether growing hydrangeas in pots or in the ground, you can maintain blue-hued blooms by acidifying the soil.
Try mulching with organic matter – apart from mushroom compost, which is more alkaline. Using ericaceous compost, such as this John Innes compost from Amazon, also tends to be effective.
You can also buy "blueing" compounds from garden centres and online, which should be applied according to the manufacturer's instructions.
Some gardeners also say adding coffee grounds to the soil can help, or working bits of rusty metal into the feeding-root area can be another option to try.
John Negus, a gardening expert and writer for Amateur Gardening, also recommends using rainwater to water hydrangeas to help keep them blue. You can collect it in a water butt – which is also a good approach if you want a more eco-friendly garden.
This can be used for hydrangeas grown in pots or in the ground. Dissolve the solution in water and then mix with the soil to help turn your pink hydrangeas blue. Dilute as directed and water weekly during the growing season.
How do you make your hydrangea pink?
Hydrangeas in neutral or chalky (alkaline) soils generally produce pink or mauve, slightly muddy-colored blooms. "Pink blooms are caused by a relatively high pH, of around 7.5–8," says John Negus.
The best way to do this is to add garden lime, such as this Westland Garden Lime Soil Conditioner from Amazon, to the soil. Follow the instructions on the pack of your chosen product, but doing it every couple of weeks during the growing season should be effective.
Adding wood ash to the soil around your hydrangeas can also help to increase its alkalinity – a useful tip for those who have invested in a fire pit for their garden.
Can you change the colour of white hydrangeas?
Hydrangeas with green or white flowers are increasingly popular nowadays, working well in both modern and romantic, cottage-garden schemes. But, unlike the blue and pink varieties, these types can not have their colour changed as they are unaffected by soil pH.
Some will, however, turn slightly pink as they age, says John Negus.
FAQs
Why are some of my hydrangea's flowers blue and some pink?
It is quite unusual to have hydrangeas that have both pink and blue blooms, but it can happen. The reason behind this is generally because there are pockets of acidity within the plant's root area.
To have more control over the soil, you may want to try planting your hydrangea in large garden planters instead.
As previously highlighted, changing the colour of your hydrangeas will be easier if you are growing them in pots as you can have more control of the soil pH due to your choice of potting compost.
Another benefit to growing them in pots is that if you have issues with your hydrangea not blooming you can easily move it to another spot to see if different growing conditions helps it to bloom once more.
The original version of this article previously appeared on Gardeningetc, a sister website to Homebuilding & Renovating.
