Science + Plants: How to Magically (& Naturally) Turn Hydrangeas from Pink to Blue 

Science + Plants: How to Magically (& Naturally) Turn Hydrangeas from Pink to Blue 

It sounds magical and mythical and just too darn good to be true! But no, it's just using scientific knowledge and a simple change in your soil that can completely transform the color of your hydrangea!  All you need to do is help your soil move from a more basic alkaline environment to an acidic environment. What is alkaline? What is acidic? Well, there is a pH scale with levels ranging from pH 0-14. Anything BELOW a pH 7 is considered acidic and anything ABOVE a pH 7 is alkaline, or basic. 7 itself is neutral.   

Natural items from our household that can help make our soil more acidic are things like coffee beans and vinegar while egg shells would help neutralize acidic environment to be more basic. The coffee grinds provide nitrogen & tannic acids to the soil.  Acid loving plants such as azaleas, blueberries, butterfly weeds, camellias, ferns, gardenias, lupines & rhododendrons especially love coffee grinds. But hydrangeas have a particularly special relationship with acidic soil! 

Generally speaking, hydrangeas in acidic soil, meaning with a pH lower than 6.0, yields blue or lavender colored hydrangea blooms. Alkaline soil, with a pH above 7.0, promotes pink and red blooms. With a pH between 6 and 7, the blooms turn purple or bluish-pink It sounds very scientific and hard but actually it is very easy; all that is needed are some common kitchen scraps. 

Most species of hydrangea will change color depending on the pH level of their soil, though it appears as though white hydrangeas are the exception to this rule. Basically, if the soil is more acidic, then the hydrangeas can absorb more aluminum from the soil. Continuing to absorb more aluminum will turn pink hydrangeas blue and keep it that way! 

Adding coffee or pine needles to your compost is simple yet very effective in adding acidity to your soil. However, if you’re using coffee in the ground soil directly, it’s best to mix coffee grounds in combination with mulch like wood chips to avoid compaction if you are not going to make compost. Using coffee directly in your soil can provide additional benefits to your soil like maintaining more moisture and it also attracts earth worms that are helpful in aerating your soil.  

Since coffee grounds don’t permanently acidify garden soil, as do peat moss or sulfur-based additives; they’ll only affect the acidity in the immediate area they’re added to; making it an amazing way to acidify plants in containers. For ground soil, you will need to work the coffee grounds into your garden soil on a regular basis to bring up the acidity over time. Remember, either way you choose to acidify your soil, it may take several months for a change in color to occur. No matter what, have fun experimenting with your soil and plants!