Have you ever planted a blue hydrangea and had it change color on you, blooming pink the next year, or even within a few months of being planted? That means the soil it’s planted in is alkaline, or “sweet.”
Not all hydrangeas can change the color of their flowers. Bigleaf hydrangea (Hydrangea macrophylla) flowers can be changed from pink to blue. Keep in mind you can’t change the color of white hydrangeas.
The color of the blooms on bigleaf hydrangeas is influenced by the pH of the soil they’re planted in. Acidic soil will make the flowers blue; alkaline soil will turn them pink. The level of acidity or alkalinity will also affect the intensity of the color. Very acidic soil will deliver deep blue flowers, highly alkaline soil will deliver very vibrant pink flowers.
You can change your pink hydrangea back to blue with soil amendment. Iowa’s soil is naturally quite alkaline, so over time, they will revert back to pink if you don’t continue to amend the soil. But, it may never go back to bright pink. Changing the color of hydrangea flowers planted in the ground takes time. It’s not an overnight process. It can take several months to change the color and even longer get very dark shades.
The Fastest Way to Turn Your Hydrangea Flowers Blue
If your hydrangea is in an area with other acid-loving plants, you can get straight to work with a soil acidifier amendment. An organic soil acidifier will adjust the pH of your soil over time. Soil acidifiers are usually a powder or granule applied on top of the soil and then watered in. Follow the application instructions on the package.
Watering your hydrangea with a fertilizer for acid-loving plants will also help, in addition to using a soil acidifier. We carry Color Me Blue Hydrangea Feed and Color Me Pink Hydrangea Feed at the garden center.
You can naturally shift your soil more to the acidic side of pH, but it’s very slow. Try adding coffee grounds, crushed eggshells, peat moss, evergreen needles, and citrus peels to the soil in the area you want to acidify. It does work, but it is a prolonged method and will take quite a while to see significant results.
Alternatively, if your hydrangea is near plants that need alkaline soil, your best bet is likely to move it, or the other plants, somewhere else. When planting your hydrangea, add a soil acidifier, and use a fertilizer for acid-loving plants for the fastest results. You’ll need to continue applying soil acidifiers once a month during the growing season to maintain the blue flowers and achieve deeper hues.
Concrete Can Affect the Color of Your Hydrangea
If your hydrangea is growing near a concrete driveway or sidewalk, you may have a more challenging time making the flowers change to, and stay, blue. This is because lime is commonly used as a binding ingredient in concrete. Lime raises the pH of nearby soil, making it more alkaline.
If your hydrangea is not near concrete, or if you haven’t planted it yet, you can test the soil where you want to plant it. Soils in Iowa are pretty alkaline across the board, but if you want to see for yourself, try a simple home test with vinegar. Scoop some soil into a pail and add 1/2 cup of vinegar; if it fizzes, your soil is definitely alkaline and will need acidifiers to turn your hydrangea flowers blue.
Excited to try this backyard experiment, but haven’t picked out your hydrangeas yet? Visit our nursery and browse the varieties available today!