Best Plants for Acid Soil
Many gardeners and homeowners may be surprised to learn that the health of many plants can be tied back to the health of the soil and its relative acidity. The acidity of soil is measured on the pH scale, which ranges from 1 to 14, one being the most acidic, 14 being basic (also called alkaline) and 7 being neutral. Most living things must stay close to a seven on the pH scale, but the majority of plants actually grow best in slightly acidic soil at a pH level of 6 to 6.8. For gardeners, the pH scale runs from about a 4 to an 8, with little plant growth beyond either end of the spectrum.
The pH scale is logarithmic, meaning that soil with a pH of 6 is ten times more acidic than a neutral seven, and that a pH of 5 would be a hundred times more acidic than a seven! The best plants for slightly acidic soil are many and easy to find, but finding the best plants for acid soil in the pH range of 4.5 to about 6.5 can be difficult without the right information.
Shrubs for Acid Soil
Wintergreen is among the most popular shrubs and best plants for acid soil, growing well in a pH range of about 4 to 6.5. The large aromatic bush remains green throughout winter and is also capable of withstanding hot summers. Trailing Arbutus provides groundcover with its creeping deep green growth and white flowers. Arbutus requires intensely acidic soil around a pH of 4.5 and is one of the best plants for very acid soil; however, it is difficult to grow in a pH over 6. Heather is another popular groundcover shrub with cheerful purple flowers that grows well in a pH of 4.5 to 6. Azaleas and Rhododendrons are among the most well-known flowering shrubs and grow very well in a wide range of acid soil from 4.5 to 6. However, not all plants will grow in all climate zones, regardless of the level of acidity. Refer to a zone chart here.
Trees for Acid Soil
Acidic soil is excellent for almost all evergreen trees, including Pines, Firs, Spruces and Yews. Evergreen trees grow best in an acidic soil with a pH in between 5 and 6. Sweetbay Magnolia grows in an even lower pH- about 4 to 5, while Holly trees grow best in a pH of 5 to 6. Many types of oak trees, like Pin Oak or Red Oak, do poorly in soil of a high pH (above 7) and prefer acidic soils around a pH of 5. Weeping willows, Dogwood and Crabapple trees also flourish in soil with a pH from about 5 to 6.5.
Flowers for Acid Soil
Some of the most beautiful flowers prefer their soil very acidic, including Bleeding Heart (5-6.5), Foxglove (5.5-6.5) and Columbine (5.5-7, depending on the many varieties) and most ornamentals in general grow well in slightly acidic soil. Roses grow well in soil of slight acidity, but can also be made to grow well in soil with a pH just below 6. Amaryllis, Phlox, Zinnia’s and Pansy’s all do well in soil with a pH as acidic as 5.
Vegetables and Fruits for Acid Soil
Most edible foods grow best in only slightly acidic soil from 6 to 6.8, but can also do well in soils as acidic as a 5. Cherry, Peach, Apple and Pear trees grow best in soil from a 6.5 to an 8 but will perform relatively well on average in a pH as low as 5.8. Despite the shortcomings of fruit producing trees, one of the very best plants for acid soil is the Blueberry Bush. With even more acidic tastes than most plants, the blueberry bush grows best in a pH of about 4 to 5 and will have difficulty producing fruit in soil of a higher pH. Kiwifruit, Huckleberry, Potatoes and Crabapple are all delicious foods that grow best in acidic soils between 5 and 6. Most vegetables have no problem growing in acidic soil and will perform well and produce healthy, tasty foods for your dinner table or local farmer’s market.
Areas with Acid Soil
Acid soil is most common in places that experience heavy rainfall and have moister environments. Areas in red have acidic soil, areas in yellow are neutral and areas in blue have alkaline soil.
Testing and Changing Your Soil’s pH
Most garden and hardware stores provide cheap soil testing kits that make testing the pH of your soil easy. Be sure to test your soil in various areas, so you can more properly gauge the overall acidity of your soil. Once you know the pH of your soil, you can either select the plants that will grow best in acid soil or in alkaline soil, or you can attempt to raise or lower the pH to accommodate other plants. It is highly recommended that you test your soil before making any pH changes.
To make acidic soil, mix equal parts Canadian peat and soil together and add a half to a quarter parts sand. Peat is very acidic, so be sure to test the soil mix and alter as needed. Add limestone to raise the pH level of your soil and lower the acidity. You can also lower the pH and make your soil more acid by adding nitrogen based fertilizers, like manure or urea with caution. Adding large amounts of manure over the years can make your soil so acidic that the plants will be unable to access necessary nutrients for years to come. For more information on liming your garden or otherwise altering the pH, go here.