Maintaining the proper pH level is essential for a plant’s ability to absorb the nutrients it needs from the soil—iron absorption is especially affected by soil pH levels. Learn which plants prefer acidity and what soil amendments help adjust soil pH levels.
Plants That Need Acidic Soil
The ideal soil pH for most landscape plants and turf grasses is around 6.5, which is considered slightly acidic. But there are some plants that require a more acidic soil in order to thrive. Here are some of the plants that need acidic soil: Shrubs:
Azalea Fothergilla Gardenia Holly Rhododendron Most evergreen shrubs
Trees:
Beech Dogwood Magnolia Pin oak Willow oak Most evergreen trees
Flowers:
Begonia Bleeding heart Caladium Camellia Foxglove Hydrangea Japanese iris Trillium Zinnia
Vegetables:
Peppers Potatoes Rhubarb Sweet potatoes
Fruits:
Blueberries Cranberries Currants Elderberries Gooseberries
Plants that require a more acidic soil than they are growing in will often signal this by developing iron chlorosis, a deficiency that causes the leaf veins or entire leaves to turn yellow. If this happens, your plants may require that you add a soil amendment to the soil they are growing in, or that you supplement their need for acid with a fertilizer designed to provide it. A variety of soil amendments and fertilizers are available to provide this assistance to acid-loving plants. Most are readily available at garden centers and home improvement stores. Before applying any soil amendment, have your soil tested to determine the types and amounts of soil amendments required.
Ways to Make Soil More Acidic
It’s best to apply sulfur in the summer or fall before the following spring planting season, digging it deep into the soil. It does not work very well to try and dig in sulfur around existing plants. As with any amendment, you need to have a soil test conducted in order to determine how much sulfur to apply in order to reach the desired pH. Iron sulfate will provide faster results than sulfur (in three or four weeks) but can damage plants if over-used. It can be dug into the soil as a powder or applied in solution and watered over leaves for absorption. However, there are recent concerns about the possibility of aluminum toxicity, which can be especially damaging to children. Aluminum can be absorbed from drinking water, and excessive use of aluminum sulfate as a soil amendment can contribute to the contamination of groundwater supplies. Many experts now recommend that aluminum sulfate is used only on hydrangeas, where the aluminum helps create the vivid blue flowers that are prized. For other plants, safer options are available, such as ammonium sulfate.
