An acid medium in gardening is considered anything below a neutral pH level of 7.0, but some plants such as blueberries will grow well in soil with a pH as low as 4.0-5.5. Azaleas, mountain laurel, and rhododendrons are other common plants that are known to tolerate acidic soils well. By acid medium, however, we are really referring to the environment where the roots of a plant grow, whether in soil, water, such as in hydroponics, or inert growing mix used in containers.
The natural acidic level of the soil can vary considerably in gardening as the roots penetrate deeper into the ground. One of the best methods for maintaining a consistent acid medium level is to root plants in compost. Mulch made of bark and ground up tree leaves, as well as traditional compost, generally has low pH levels, and therefore serves as a excellent acid medium for plants that grow well in low pH conditions.
Most plants thrive in neutral to slightly acidic soils, but certain regions and climates are predominated by acid-loving plants. An example of this is the Pacific Northwest area of the United States and Canada that has a large number of flowering plants that thrive in an acid medium. These include hydrangeas, preferring a pH of 4.5-5.5, many varieties of heaths and heathers which are also common to England and Europe and grow in pH soils of 5.0-6.2, and popular flowering woodland plants such as the bleeding heart, growing in pH 5.0-6.5.
Temperate forest environments in general often support acid-medium-based plant life. One of the reasons for this is that such forests are often dominated by evergreen trees of many species, such as pines, firs, and spruces. All of these types of trees are acid-medium-based and support a forest floor environment that sustains plants with similar needs. Berry bushes found in these climates, such as blueberries, raspberries, strawberries and blackberries, as well as potatoes, also favor an acid-medium-based soil.
Altering a soil's pH level with soil amendments or synthetic fertilizers to lower the pH level is common, though not considered as effective long-term as using natural materials such as compost. If a soil is too naturally acidic for the types of plants being grown, the pH level can easily be raised near a neutral of 7.0, which most plants tolerate well. Mixing powdered lime into the soil, available at most garden centers, will raise pH levels at minimal cost.
