Climate, native plants and a wide range of other environmental factors dictate the acidity or alkalinity of the soil in any particular area. Soil with a pH level below 7.0 is considered acidic, and can be inhospitable to certain kinds of plants and flowers. Other plants, however, require moderately or heavily acidic soil in order to grow and thrive. If you test the pH of your garden soil and find it to be considerably below 7.0, consider planting the flowers that love acidic soil the most.
The azalea is a popular flowering garden shrub with thousands of distinct, named varieties. Though some varieties have specific tolerance guidelines and care instructions, most azaleas prefer a moist, acidic soil and require plenty of water and shade. Azaleas bloom in the spring with big, bright flowers that vary by variety; common colors include white, purple, red, pink, yellow and orange, though some flowers contain two colors in varying patterns. With proper care and management of shade and soil pH, evergreen azaleas can be maintained for decades.
Rhododendron is an entire genus of flowering plants that includes more than one thousand species, including many evergreen species. Most rhododendrons grow as shrubs or small trees with broad leaves and big, brightly colored flowers that bloom in the spring. Evergreen varieties must be protected from harsh wind and direct sunlight during the winter season. Rhododendrons prefer a fairly acidic soil with ample drainage; in areas where the soil does not drain easily, rhododendrons may need to be grown in raised beds where drainage can be more easily controlled.
Mountain laurel is a flowering evergreen shrub that is native to roughly the eastern half of the United States, and is the state flower of Pennsylvania and Connecticut. It needs partial shade, wind protection and an acidic soil environment in order to thrive. Though it is harmless to dogs, cats and most other small household pets, mountain laurel is highly toxic to humans and many large, wild mammals. Between May and June, a mature shrub will produce large clusters of white, pink and red blossoms that are shaped like open umbrellas.
Heather is a common plant in garden landscaping and in flower arranging, and is characterized by thin, upright stems studded with tiny, bright flowers. The fragrant blooms of this ornamental shrub vary through a full range of whites, pinks, purples and reds. Though fairly durable, heather thrives best in moist, acidic soil and temperate conditions. Many heather shrubs are appreciated as much for the beauty of their distinctive foliage as they are for their flowers.