Acidic soil has a value of less than 7.0 on the pH scale, a scale that measures the degree of acidity or alkalinity from zero to 14. Most garden plants grow well in a slightly acid soil, pH 6.5, while others, such as desert plants and many annual flowers and greens, need more alkaline conditions. A score of 5 on the pH scale is considered very acidic.
Acid-Loving Shrubs and Trees
Shrubs that prefer soil of pH 5 include azaleas and rhododendrons, hydrangeas, mountain laurel, skimmia, loropetalum, Japanese pieris, bottlebrush, fothergilla, camellia and juniper. Trees that thrive in acid soil include crabapple, birch, dogwood, oak, spruce, yew, hemlock, pine, black gum, golden larch, Cryptomeria japonica, Carolina silverbell, sourwood, Douglas fir and American beech.
Acid-Loving Fruits and Vegetables
All the members of the Vaccinium genus prefer acidic soil, including blueberries and huckleberries. Other fruits that enjoy these conditions are watermelon, rhubarb, strawberries and raspberries. Acid-loving vegetables include potatoes, sweet potatoes, shallots and eggplant.
Acid-Loving Annuals and Perennials
The common perennial groundcover ajuga prefers highly acidic soil, as do heathers, bog rosemary, lilies, lupin, ferns, dicentra, astilbe, bergenia, daffodils, calla lilies, foxglove, gentian, primroses, trillium, epimedium, bluebells and goatsbeard. Annuals prefer soil at pH 6.5, but a few will tolerate soils slightly more acid. They include Million Bells (Calibrachoa), Nicotiana, marigolds and verbena.
Changing the Soil
If your soil is too alkaline to grow acid-loving plants, you can mix sulphur with the soil when you plant, according to package directions. Using acidic materials such as pine needles or oak leaves to mulch your plants also helps add acidity. For soils that are too acid, the solution is to add lime in the form of calcium.