Hydrangeas are beautiful shade loving flowers that can grow into huge bushes. Most striking is their large mophead flowers that can be light to dark pink, blue to purple, or white in color. If you have lovely white hydrangeas, you cannot change their color. But you can change the color of hydrangeas that are pink or blue.
It is fairly easy to change the color of hydrangeas from pink to blue, but more difficult to change them back or convert a blue one to a pink hydrangea. If you want to change colors, from blue to pink, you should consider keeping the plants in pots, since you can better control the type of soil used and its components.
Getting blue hydrangeas is actually very simple. You can take the average pink hydrangea, plant it in a pot and add some metal to the soil. Putting in several nails right below the plant is an excellent idea. If you want to plant the hydrangea in the ground, simply add a few aluminum nails to the hole right before you add the hydrangea. You can always add more if the plant exhibits pink flowers at a later stage.
Another way you can change the color of hydrangeas from pink to blue is to add a small amount of aluminum sulfate to the plant. This should be done to mature plants only, and added extremely sparingly since the chemical can cause irreparable root damage. You should also try to use soil with a low pH. If you need to lower the pH, this can be achieved by using soil with lots of potassium, or by adding organic or composting material. Even dumping a bunch of coffee grounds on the soil will lower its pH.
A lower pH means the metals in the soil are more easily absorbed by the plant, and will change the color of hydrangeas from pink to blue, though this is a gradual process and can take a few months to a few blooming cycles to completely change. You also may need to occasionally retreat the plant to keep flowers blue. Once the plant stops absorbing metals, the blooms will likely turn back to pink.
Usually though, it’s a little harder to change the color of hydrangeas from blue to pink, especially if they’re planted in heavily metallic soil. Again, soil is key and instead of lowering the ph, you want to raise it by adding phosphorous rich soil to the plant. Phosphorous acts like a barrier preventing metal from being absorbed by the plant.
If you want to keep a pink hydrangea pink, take a good look around your neighborhood at the color of your neighbor’s hydrangeas, especially those planted in the ground. If most are naturally blue, chances are you have soil with a significant amount of aluminum in it. Keeping the plant blooms pink, then, is best achieved if you plant in pots. On the other hand if most of the ground planted flowers are pink, you’ll probably have good luck simply planting the flowers in the ground. Another tip is to plant the flowers near the sidewalk or a concrete driveway. This causes lime to leak into the soil, which helps prevent the plant from absorbing aluminum.