The Kitchen Waste That’ll Turn Your Hydrangeas Blue

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The Kitchen Waste That'll Turn Your Hydrangeas Blue

The Kitchen Waste That’ll Turn Your Hydrangeas Blue

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Blue hydrangeas are a beautiful addition to any front lawn. Not only will they boost your curb appeal, but they will add a classic pop of color to your landscaping. The color blue is timeless and makes you think of an idyllic homestead, bringing that same vibe to your humble suburban or city home. However, the blue hydrangea isn’t always easy to keep, since the bloom can change in color. The good news is that if you’re losing your blue flowers, you only need a few coffee grounds.

That’s because the flower color shifts depending on the acidity of the soil it’s planted in. When the dirt is alkaline — clocking in at pH 7.0 or above — the flowers turn pink. When the soil is neutral — consisting of a pH between 6.0 and 6.2 — it will be white. But for blooms to turn blue, you need acidic soil, with a pH of less than 6.0. Since coffee is naturally acidic, it can help you keep — or acquire — that vibrant blue color. Here’s how.

How to use coffee grounds to turn hydrangeas blue

coffee grounds

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When trying to change their hydrangea colors, some gardeners prefer to try the coffee ground hack before investing in fertilizers that will change the pH of their soil. That’s because it’s cheaper and already on hand. If you make coffee each morning, accumulating enough grounds for this gardening hack should be relatively easy. The first thing to do is to test your pH levels with a soil kit. You can pick one up at any garden center, and it will tell you how far you have to move the pH level to get your desired color. It will also protect you from making your dirt overly acidic, which can be detrimental to the plant. Once you have that info, it’s time to grab the grounds. 

It’s best to do this during late fall, well before your flowers begin to bloom in the next season. This will ensure the new buds come in blue rather than the current color. When amending the soil with grounds, you don’t want to simply dump them into the dirt and call it a day. Instead, get your gardening gloves on and spread it across the soil and work it in. You can repeat this twice during the season, adding grounds whenever you add fertilizer.

Caveats to keep in mind

white hydrangea

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Before attempting this hack, one thing to keep in mind is that there are a couple of varieties that cannot produce blue flowers, even when the soil is amended. Specifically, white hydrangeas won’t color shift, and this includes Oakleaf hydrangeas, Annabelle hydrangeas, and Peegee hydrangeas. They always stay stubbornly white, and if they turn slightly pink with age, that doesn’t have to do with soil acidity. Only blue and pink versions can change colors. 

The second thing to keep in mind is that this hack can sometimes be a hit or miss. A good amount of gardeners have reported success color-changing with coffee grounds, but it doesn’t have a 100% success rate. In the end, you might need to switch to fertilizers that can make the soil more acidic, but it’s still worth a try before taking more drastic measures. Just know it will likely take a whole season before you begin to see a change, since this process is often slow and long. 

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Dr Heidi Parkes

By Dr Heidi Parkes

Senior Information Extension Officer QLD Dept of Agriculture & Fisheries.