The soil pH can change the health of plants and the colors of flowers!
pH of Soil
The pH of the soil determines the variety and quality of plants that can grow healthily in it. Flower and fruit bearing plants and trees also have a pH need, as much as the Zone in which they grow!
Hydrangeas seem to reflect the change in soil pH in their flower colors in itself. If you are growing Hydrangeas, try this at home.
For blue flowers, the hydrangeas need to be grown in acidic soil with a pH of 5.5 or lower. For pink flowers, the plants need neutral to alkaline soils (pH 6.5 and higher). For purple blooms (or a mix of blue and pink flowers on the same plant), the pH of the soil must be between pH 5.5 and 6.5
Flower colors depend on the concentration of aluminum ions in the soil. When soil has more aluminum it, it tends to be acidic, less of it makes the soil alkaline. For pink hydrangeas, reduce the aluminum content in the soil.
tricks to try at home
Dilute 3/4 cup vinegar in a gallon of water and use it next time you water the plants. While vinegar is harmful for many plants, when used in extremely diluted amounts, we can see the flower colors changing easily with hydrangeas.
Epsom salts work well to reduce the pH of the soil as well.
Fertilizers with higher sulphur or sulphates help to reduce pH as well.
When trying out different combinations, try these in smaller varieties in potted plants, before trying it on garden soil and changing the overall pH of the soil nearby.
Off the shelf products
If you are interested in buying an off-the-shelf product, look for Hydrangea color influencing kits. There are plenty available online.
Soil acidifiers and/or Garden lime (for alkalizing) work very well for both extremes!
When to get expert help
Changing the pH of the soil has some side effects. If done incorrectly, micro organisms in the soil are impacted, and the tendency to develop mushrooms, fungus infections increases. You will start seeing the changes after one or two seasons. If you see any continuing symptoms that requires higher order care, do have your lawn or garden evaluated by a landscaper. It helps in the long run!