How to Turn a Hydrangea Blue Using Coffee Grounds

Turning a Hydrangea Blue NaturallyNow that summer has come and gone, it is time to reevaluate the garden. Did your hydrangeas look their best? I adore the vivid hues of a Nikko Blue hydrangea, but my soil is so alkaline, that the best they have ever done is an insipid pink-lavender. Until now! I’ve learned that turning a hydrangea blue naturally, with no harsh chemicals, can actually be easy. Just add… coffee!

First, a word of warning. Not all hydrangeas are actually able to produce show stopping blue flowers. Best suited are mopheads and lacecaps (Nikko Blue, Pretty in Pink, Forever Pink and Blue Deckle, for example), which have blooms that vary from pink, to purple, to stunning blue. Based on the chemistry of the soil, these plants can vary dramatically from one shrub to another and even from flower to flower! The more acidic the soil, the bluer the bloom.

The first step is to test the pH of your soil. A pH of less than 7 is considered acidic and 7 is neutral, while anything higher than 7 is alkaline (referred to by some gardeners as “sweet soil”). If your soil is very alkaline, it will contain a great deal of sodium, calcium and magnesium. And, because alkaline soil is less soluble than acidic or neutral soil, the availability of nutrients can be limited, resulting in stunted growth and nutrient deficiency of your plants.

Turning a Hydrangea Blue Naturally using coffee grounds

Turning a Hydrangea Blue Naturally using coffee grounds

Testing your soil’s pH should be on your late summer/early fall gardening checklist. This will give you the information you need to amend the soil before winter, as well as first thing in the spring. This gives you enough time to provide hydrangeas with the acidity they need in order to produce big, beautiful blue blooms next summer. Soil pH testing kits are widely available at specialty home and garden stores, big box retailers, and even on Amazon.

Once you are armed with your pH level, it is time to start adjusting your soil. To adjust the acidity of soil, coffee grounds are the simple, easy and free solution. The increased acidity from coffee grounds makes it easier for the plant to absorb naturally occurring aluminum in the dirt, resulting in beautiful blue flowers.

To use coffee grounds as fertilizer, simply work the grounds into the soil around your plants (a great use for stale coffee). Leftover, diluted coffee works well too!

This is not a quick process. In order to maintain growing conditions that result in blue blooms, you will need to apply many times. The trick is to be consistent from fall through spring, well before the hydrangeas bloom. The earlier you add coffee grounds to the soil, the earlier you affect the bloom color of the flower, since buds begin to develop during the winter.

In addition to gorgeous blue blooms, adding coffee grounds to the soil has some other benefits, too. Coffee grounds will improve drainage, water retention and aeration of the soil. They also help microorganisms that are beneficial to plant growth thrive, and attract earthworms.

Turning a Hydrangea Blue Naturally

Turning a Hydrangea Blue Naturally using coffee grounds

Many gardeners swear that coffee grounds are also helpful in keeping slugs and snails away from plants. Similarly, the coffee is helpful as a cat repellent and will keep neighborhood cats from using your flower beds as a litter box.

So, brew an extra pot and sit down to a delicious cup of Joe… with your plant!

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Turning a Hydrangea Blue Naturally using coffee grounds


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  1. 7

    This is good to know, I didn’t realize all this! My neighbor’s hydrangea’s are always very blue, and I’ve marveled at them, so full and perfect, too, not sure about the soil.

    • 8

      The coffee actually works wonders. I keep a jar next to the coffee maker to save the grounds. Once a week, I add them to the soil. Come spring, the flowers are SO blue!

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