Fungal problems are some of the most persistent issues facing gardeners. Even indoors, a variety of fungal organisms can affect your plants, ranging from common problems like anthracnose to opportunistic infections that attack weakened plants. If your plants start to suffer from unusual spotting or funny colored growths, the problem is likely a fungus.
Issues Caused by Fungi
Fungi thrive on the energy from the plants on which they live. As the fungus grows, the plant withers. Plant fungus can quickly damage and even kill plants. Different types of fungi have a variety of appearances that include wilting, scabs, moldy coatings, blotches, or rotted plant tissue. Some come through the air via spores and attach onto the plant's leaves. Other types live in the soil and can enter a plant through the roots. Root-based fungi can kill the roots or block the water-conducting cells, causing the plant to wilt and eventually die.
Effectiveness of Baking Soda
Outdoors, gardeners can use a variety of antifungal agents to control fungal problems on plants. Popular antifungal agents contain copper and sulfur, which are both toxic materials. These chemicals can be used indoors, however safety instructions must be followed very carefully. These chemicals are toxic to mammals, so avoid ingesting them and wear protective clothing when applying them to your plants. If any pets or children will be interacting with the treated plants, it may be best to avoid using these chemicals or move the plants to a location where they cannot be disturbed.
If you prefer a gentler solution, try using baking soda. Baking soda (sodium bicarbonate) is an antifungal agent and can even kill some established forms of fungus. Research has shown it's effective against some kinds of black spot and powdery mildew. Best of all, baking soda is completely non-toxic for mammals, readily available in any grocery store, and inexpensive.
Making the Spray
Make a typical baking soda spray by dissolving 1 teaspoon of baking soda into one quart of water. You can add a few drops of insecticidal soap or liquid soap to help the solution spread and stick to the leaves. Only use liquid soap, like Ivory, and not laundry detergent. Stir this mixture around and then pour it into a clean, empty spray bottle.
Spray the plant completely, reaching both the upper and lower leaves, and let the plant dry. Repeat the application as necessary to control the fungal problem. If the fungus continues despite the repeated application of baking soda, consider using a stronger antifungal agent. Baking soda sprays should be labeled and stored out of reach of children. If you have leftover spray, it can be left sealed and used next time. Give the spray bottle a gentle shake prior to use.
Constant use of a baking soda spray on plants will eventually seep through to the soil below. Bicarbonate can accumulate in the soil, impact the nutrients in the soil and may lead to slower plant growth. There are so many factors impacting a plant's ecosystem that it is hard to predict what outcome a baking soda spray will have on a particular plant. If you notice plant damage or lower quality blooms, stop applying the baking soda spray to your plant.
Copper Sulfate General Fact Sheet. National Pesticide Information Center.
12 Non-Toxic Ways to Use Baking Soda. Eco Watch.
Martínez-Cuenca, MR., Iglesias, D.J., Forner-Giner, M.A. et al. The effect of sodium bicarbonate on plant performance and iron acquisition system of FA-5 (Forner-Alcaide 5) citrus seedlings. Acta Physiol Plant 35, 2833–2845 (2013). https://doi.org/10.1007/s11738-013-1317-7