Hydrangeas are bold, bright and beautiful flowers that help to bring a burst of colour to gardens, but it’s not just their striking blooms that make them special. Some varieties of hydrangea have the unique ability to change the colour of their flowers depending on the pH level of the soil they’re planted in. Both bigleaf hydrangeas (Hydrangea macrophylla) and mountain hydrangeas (Hydrangea serrata) are capable of such colour changes, specifically shifting from pink blooms to vibrant blue and vice versa. The colour change is partly due to the plant’s ability to absorb aluminium, which is influenced by how acidic or alkaline the soil is.
While hydrangeas mainly flower in shades of blue, pink, purple and white, it is possible for gardeners to influence the colour by changing the pH of the soil and this can be done with the use of kitchen scraps, like grapefruit.
If you want to add a pop of blue to your garden then you’ll need to make your soil more acidic and natural ingredients are a good way to do this.
According to gardening experts, the peel from grapefruit can be used to make soil more acidic as it contains high levels of citric acid, so as it decomposes this is released into the soil, helping to lower the pH.
This is good news for acidic-loving plants like hydrangeas which thrive in these conditions and this low pH level can then encourage blue blooms. Plus the peel is also rich in nitrogen, phosphorus and potassium which all help to promote healthy root and leaf growth.
If you don’t have any grapefruit, the same effect can also be achieved using the peel of other citrus fruits like orange, lemons and limes, although these are smaller fruits so you might need to add more to your soil.
Real Flowers explains: “Depending on the acidity of the soil, the colour of Hydrangea flowers can change from blue to purple to pink. Adding coffee grounds, citrus peel or eggshells renders the soil more acidic and causes flowerheads to become purple, with an increase in acidity turning blooms blue.”
Bay Ave Plant Company adds: “To make your blue flowers more pink or your pink flowers more blue, you need to change the acidity of the soil. Changing the pH of the soil is as easy as adding coffee grounds or a ground up citrus peel. Make sure to work this mixture into the soil around the base of the hydrangea plants.
“If you want your flowers to remain that beautiful blue or pale pink, the upkeep is easy. For blue flowers, simply fill a bowl with coffee grounds, orange peels, or even crushed egg shells. Keep the bowl in the kitchen and once it is full, bring it outside to feed the hydrangeas.”
Gardeners should be aware that the process of turning hydrangeas a more vibrant blue won’t happen overnight and will require some time and patience to produce the colour, so if you want to give the plant an extra helping hand adding aluminium sulfate to your soil as well can really help.
Dammanns Garden company adds: “Organic materials, such as coffee grounds, egg shells or citrus fruit peels are another, more natural method of making soils more acidic. Simply grind them up and work them into the ground. These changes will happen gradually, so it might take an entire year of doing this consistently for it to reach the right acidity.”