Love your hydrangea blooms but want to change up their colour? Many hydrangeas will go through a slight colour change when transplanted due to adjusting to their new soil when you first bring them home. But if you really want to shake things up, try changing the colour of hydrangea flowers with this simple little soil hack!
Hydrangea varieties such as Hydrangea macrophylla and H. serrata can range in colour from pink to blue, with every shade of fuchsia, plum, and periwinkle in between. The blooms can change colour based on the amount of aluminum the plants absorb from the soil, which depends on the soil pH.
But I’ll admit that the process isn’t easy. It can take well over a year to change the pH of your soil and it requires quite a bit of work.
Instead, I suggest becoming content with the hydrangea colours you already have. If you really want a pink or blue hydrangea, I suggest buying a variety that’s already in that colour. This is the best way to ensure you get the colour you want.
But, if you have a hydrangea already in your garden and are just dreaming of a sea of pink or blue, you can try changing the colour of your hydrangea with these tips.
This post will cover…
How to Change the Colour of a Hydrangea
High levels of aluminum in the soil plus an acidic soil pH will generate the coveted bright blue to purple flowers. Less aluminum in the soil and/or alkaline soil will create a variation of pink blooms. Not all hydrangea species change colour, however. White ones do not change, and some varieties are bred for a specific colour palette.
And before you get too excited, you cannot change the intensity of the hydrangea colour; that is more dependent on the environment or weather. Although I must say that changing the hydrangea bloom colour so drastically is pretty darn exciting!
The first thing you need to do is test the pH of your soil. Acidic soil (lower pH) will yield blue flowers and alkaline (higher pH) will give you pink flowers. You can buy a soil test kit at your local garden center to determine the pH of the soil, but here is a quick and simple way to figure out your soil’s pH with ingredients from the kitchen.
Once you know the general pH of your soil, you can adjust it to get pink or blue hydrangea blooms.
Changing the Colour of Hydrangea Flowers to Blue
If you have pink hydrangeas (because your soil is alkaline) and you want them to be blue, you need to make the soil acidic by increasing the presence of aluminum.
You can achieve this by adding amendments to you your soil like pine needles, compost, coffee grounds, elemental sulphur and gypsum, or use an organic fertilizer containing cottonseed meal when feeding the plants.
Recommendations to add aluminum sulphate to the soil are often not necessary and could be harmful. Aluminum is plentiful and not an essential plant nutrient, and too much of it can be toxic.
Keep in mind that changing the pH of your soil is a gradual process and will not result in deep blue blooms overnight. It can take up to a year for the colour change to happen.
If your soil is naturally alkaline, you’ll have to add an aluminum source throughout the growing season to keep them blue. One of the most common amendments is sulphur. To use it, add ½ cup of sulphur per 10 square feet. Repeat the process every 3 months.
Changing the Colour of Hydrangea Flowers to Pink
To change hydrangea flowers from blue to pink, you need to remove the aluminum from the soil. The only way to do this is to add garden lime to the soil to help raise the pH.
Garden lime is ground limestone rock, which is a slow-release amendment for treating acidic soil. It contains calcium carbonate, so it not only raises the soil pH, but it also adds calcium.
Sprinkle 1/2 cup of garden lime per 10 square feet. Again, you will have to add the lime every 2 months throughout the growing season to keep the blooms pink.
Frequently Asked Questions About Changing Colour of Hydrangeas
Epsom salts are neutral and will not change the pH of your soil. Therefore, they will not affect the colour of your hydrangeas. Read more about the myths behind using Epsom salts in the garden here.
Unlike blue and pink hydrangeas, white hydrangeas won’t change colour based on the soil’s pH. To keep white blooms, simply keep your plant healthy and happy with the right amount of water, sunlight, and nutrients.
Baking soda is alkaline, adding it to the soil will reduce acidity. To change hydrangeas blue, you want them to be more acidic, not less acidic.
However, baking soda is a poor soil amendment. Even if you want to change flowers from blue to pink, baking soda wouldn’t be the way to go. You would need a lot of it to get the job done. There are easier and more inexpensive methods.
Hydrangeas change colours as they age throughout the season. They have the brightest pigment at the beginning of the blooming season before turning green and then brown. Some varieties also turn green quicker than others do.
If it’s the beginning of the season and they’re already turning green, then the hydrangea may not be getting enough light or undergoing heat or drought stress. Any energy will go into the survival of the plant rather than the flowers.
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