You may have many questions about the blue hydrangea. You may be wondering about why blue hydrangea are so expensive, sometimes costing hundreds of dollars per plant. It is because blue hydrangeas do not automatically grow blue when they are planted. The blue color comes from aluminum in the soil you grow the plants in. If your soil has no aluminum, your hydrangea will grow pink. If the soil has some aluminum, you could end up with a plant that is either purple or has both blue and pink blossoms!
If you have a white hydrangea plant, you can't change its color. If you have a blue or pink plant, however, it is possible to change the color of the flowers over time with the proper care. You cannot change the vibrancy of the flowers, though. If you start with a pale pink hydrangea, you could end up with a pale blue hydrangea. If you start with a red hydrangea, you might get a brilliant blue if your experiment is a success. The saturation of the color depends upon your plant's genes, which is why some are so much more expensive than others.
Changing the color of your hydrangea is obviously much easier to do if you are raising the flower in a pot. The best way to get a blue hydrangea is to start with acidic soil. If you do not naturally have acidic soil, you can make some by adding lots of compost and decayed organic matter such as grass clippings, discarded produce and fruit and vegetable peels and old coffee grounds. Compost will lower your soil's pH and add valuable nutrients to make your plant healthy.
In order to obtain a blue color, your soil must have access to aluminum. You can add aluminum sulfate to your soil around your hydrangeas to achieve this. Do not attempt to add aluminum to the soil around young plants that are fewer than two or three years old, though, as this could poison them. If you have mature hydrangeas, mix up a solution of half an ounce of aluminum sulfate to one gallon of water. Pour this solution on your plants throughout the growing season, after you have watered them. Do not add too much solution or you could burn your plants.
In order to consume the aluminum, the hydrangeas must have acidic soil. If you did not amend your alkaline soil, the hydrangeas will not turn blue no matter how much aluminum you pour on them. If your soil is naturally acidic and has aluminum, though, your hydrangeas should naturally turn blue.
Give your hydrangeas a fertilizer that is high in potassium and low in phosphorus to produce the color you want. Do not give them bone meal or superphosphates. If your soil is chalky and has no aluminum naturally, you will need to perform a lot of maintenance on your plants to retain the blue color. Make sure that you are not adding high pH water to the soil. You should also avoid planting your hydrangeas near sidewalks or concrete foundations, since the lime will leach into the soil. Planting blue hydrangeas might be hard work, but it’ll all be worth it when your first bloom comes in.