Answer: Generally speaking, most cultivated plants are happy in soils with a pH of 6.0 to 7.5. Since 7 is neutral on the pH scale, anything slightly more acidic or slightly more alkaline shouldn't make much difference to most plants.
There are some real acid-lovers, such as blueberries, azaleas and rhododendrons, and there are some plants that prefer alkaline soils, such as lilac and cacti. Most areas with high rainfall will have acidic soils and areas with little rainfall will have alkaline soils. That's just a general observation, and soils may vary.
Some of the flowering plants that thrive in my acidic soil include Iris kaempferi, Erica, Lewisia, Tropaeolum (flame flower), Dierama (wandflower), Lupine, Calceolaria, Primula, Narcissus, Lilium speciosum, Muscari, Gentian, Andromeda (Bog Rosemary), Begonia and Shortia.
I've also had good results with vinca minor and ajuga as groundcovers.
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