How to Choose a Fertilizer for Acid-Loving Plants

Common Types of Acid-Loving Plants

Most plants prefer a soil pH between 6 and 7.5, which is neutral. Other popular plants, trees, and shrubs prefer acidic soil, which typically has a pH level between 4 and 5.5. These include:

• Azaleas.
• Blueberries.
• Calla lilies.
• Camellias.
• Conifers.
• Crepe myrtles.
• Dogwoods.
• Gardenias.
• Heather.
• Holly.
• Hydrangeas.
• Magnolias.
• Potatoes.
• Rhododendrons.
• Strawberries.
• Wood anemones.

If you’re trying to grow any of these species in neutral or alkaline soil, be prepared to add a fertilizer for acid-loving plants.

How to Measure Your Soil’s Acidity

Before planting an acid-loving species, measure your soil’s pH level to determine if it needs amendments. You can easily find pH test kits and meters to buy online, or you can send a soil sample to your local county extension or soil testing laboratory. These latter resources will provide you with a more detailed and in-depth analysis than a DIY kit.

Regardless of which type you choose, follow the lab or label’s recommendations for altering the pH level. Some might recommend adding elemental sulfur, while others might suggest ammonium sulfate or aluminum sulfate — all of which lower pH when mixed with soil. Your test results might also indicate that your soil needs other nutrients, such as calcium or gypsum. The goal is to modify your soil so it can provide your acid-loving plants with the best environment in which to grow.

Realize that even after making adjustments, your soil will gradually return to its original pH level. You might need to perform regular soil tests to monitor it and apply repeat treatments.

Signs Your Soil Isn’t Acidic Enough

Another telltale sign, aside from a soil test result, that your soil isn’t acidic enough for your plants is a condition called chlorosis. Alkaline soil can block acid-loving plants’ access to nutrients such as iron, magnesium, and nitrogen. This causes their leaves to turn yellow or light green. The discoloration can vary, however, depending on the deficiency. 

An iron deficiency causes the leaves to yellow only between their veins and tends to affect younger leaves. A magnesium deficiency causes yellowing from the outer edges in, especially in older leaves, and is more common in sandy soils. A nitrogen deficiency causes an even yellowing of all types of leaves.

If you don’t correct the pH level, the plant’s health can deteriorate and branches and leaves can fall. The plant will be weaker and less capable of combating insects and disease.

How to Make Soil More Acidic

If your soil is alkaline or you garden with a neutral soil medium such as coco coir (made from the husks of coconut hulls), you’ll need to supplement with an appropriate fertilizer. A number of products and DIY concoctions can serve as fertilizer for acid-loving plants. Here are some ways to make your soil more acidic:

• Coffee grounds: Acid-loving rose plants benefit from a sprinkling of coffee grounds, which are naturally acidic. Place used coffee grounds on a newspaper or baking sheet in the sun and allow them to dry for two to three days before applying them to the plant’s base.
• Compost: This organic material not only increases soil acidity but also provides other nutrients, such as magnesium and nitrogen, that plants need to thrive.
• Eggshells: Eggshells, which are made of calcium carbonate, serve as an effective fertilizer for acid-loving plants of all kinds. Place dried eggshells in a blender to grind them into a powder, then dust them over your soil.
• Epsom salt: Mix 1 tablespoon of Epsom salt with 1 gallon of water, and water your vegetable, rose, and houseplants with this solution once a month. The magnesium and sulfate in the salts provide these plants with nutrients lacking in neutral soils.
• Fish tank water: Water any acid-loving plant with dirty fish tank water, which is rich in nitrogen. 
• Peat moss: Peat is highly acidic; adding 1 to 2 inches of this organic compound to the topsoil of container plants and small gardens can effectively lower pH levels.
• Pine needles: Mulch with pine needles, which help soils stay moist and serve as a fertilizer for acid-loving plants.
• Vinegar: Mix 0.5 to 1 tablespoon of white vinegar with a gallon of water and use this solution to water your vegetables and houseplants (particularly those in containers) every three months. Its acetic acid will help lower the soil’s pH.

Solutions such as vinegar are fast-acting, while organic materials such as compost, pine needles, and peat moss lower pH levels over time. It could take months for these fertilizers to be effective, depending on the soil’s temperature, moisture, and bacteria presence. 

If you buy a commercial fertilizer for acid-loving plants, look for products containing:

• Ammonium sulfate.
• Ammonium nitrate.
• Elemental sulfur.
• Granular sulfur.
• Iron chelates.
• Iron sulfate.
• Sulfur-coated urea.

Follow label directions for application very closely if you opt to go this route. Some ingredients, such as ammonium sulfate, are very strong and can burn leaves and plants if used improperly or in excess. If your soil does become too acidic, blend it with a neutral growth medium such as coco coir to right the ship.

Monitor your soil’s pH regularly and watch for signs of chlorosis. Then choose the appropriate type of fertilizer for acid-loving plants depending on what you’re growing and where. Follow your soil test and fertilizer label’s recommendations closely to avoid burning plants or making the soil too acidic.