Image by Dwight Sipler
By Heather Rhoades
For gardeners growing an acid loving plant, like blue hydrangea or azalea, learning how to make soil acidic is important to its overall health. If you do not already live in an area where the soil is acidic, making soil acidic will involve adding products that lower the soil pH. Soil pH measures the alkalinity or acidity levels, which range from 0-14 on the pH scale. The middle (7) is considered neutral while levels falling below 7 are acidic and those above that number are alkaline. Let’s take a look at how to raise acid level in soil.
What Types of Plants Grow in Acidic Soil?
While most plants grow best in soils that are between 6 and 7.5, others are favorable to more acidic conditions. Some of the most common and sought-after plants actually prefer acidic soil, even though many of them may be grown in a wide range of growing conditions.
The acid-loving plants that you can grow in acidic soil include:
- azaleas and rhododendrons
- wood anemone
- bleeding heart
- various carnivorous plants
- holly shrubs
- crepe myrtle
- calla lilies
- pine trees
Even blueberries thrive in this type of soil pH.
How Do I Make My Soil More Acidic?
If your plants aren’t growing in your soil conditions because of too much alkalinity, then it may be necessary for you to learn more about how to raise acid level in soil pH. Before making soil acidic, you should first perform a soil test, which your local County Extension Office can assist you with, if needed.
One of the easiest ways to make soil more acidic is to add sphagnum peat. This works especially well in small garden areas. Simply add an inch or two of peat to the topsoil in and around plants, or during planting.
For another quick fix, water plants several times with a solution of 2 tablespoons vinegar to a gallon of water. This is a great way to adjust pH in container plants.
Acidifying fertilizers can also be used to help raise acidity levels. Look for fertilizer containing ammonium nitrate, ammonium sulfate, or sulfur-coated urea. Both ammonium sulfate and sulfur-coated urea are good choices for making soil acidic, especially with azaleas. However, ammonium sulfate is strong and can easily burn plants if not used carefully. For this reason, you should always read and follow label instructions carefully.
In some instances, applying elemental sulfur (flowers of sulfur) is effective. However, sulfur is slow acting, taking several months. This is also most often used by large-scale growers, rather than the home gardener. Granular sulfur is deemed safe and cost effective for smaller garden areas, with applications of no more than 2 pounds per 100 square feet.
Sometimes recommended as a method of lowering the pH enough to turn hydrangea blooms from pink to blue is iron sulfate. Iron sulfate acts more quickly (2-3 weeks) but should not be used on a regular basis, as heavy metals accumulate in the soil, becoming harmful to the plants.