•Add organic matter.
The most organic way to lower your soil’s pH level is to add soil amendments. Use organic materials like mulch, pine needles, sphagnum peat moss, compost, and coffee grounds.
Collect 2 tablespoons of soil in a bowl.
Moisten it with distilled water.
Add 1/2 Cup of baking soda
If the mixture fizzes
You have Acidic soil
Soil pH can be lowered by increasing soil nitrogen. Adding compost, manure, or organic soil amendments like alfalfa meal to the soil can help drop pH over time by increasing bacterial populations
Generally within the first full year of growth it may begin to produce a more violet bloom, and by the second year they are leaning toward a pink blossom. This means your soil is too acidic.
Purchase this product and use it around the base of your Hydrangea every three months, beginning in the spring
Periodically soil pH testing is a very good idea, as waters can flow from other areas and this can greatly affect the soil in your garden beds.