Answer: Although soil pH can affect the color of hydrangea flowers, to my knowledge it won't affect a rose bushes bloom color.
Soil pH is a measurement of the soil's acidity or alkalinity. A pH of 7 is neutral. Soils with a pH below 7 are acidic and become more acidic the lower the number goes. Soils with a pH above 7 are alkaline and become more alkaline as the number goes up.
Roses prefer a slightly acidic soil pH, ideally between 5.8 and 6.2. A soil pH that is too high or too low interferes with or prevents the chemical reactions that make nutrients available to plants. You can purchase home soil test kits or send a sample off to a testing lab to determine your soil's pH.
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