Sodium bicarbonate can benefit certain plants, but it should be used carefully
- Fungal Prevention: Baking soda can help prevent fungal diseases like powdery mildew, black spot, and leaf blight on certain plants, including roses, cucumbers, and tomatoes. According to CSU Extension, baking soda may be used as a nontoxic control for mildew when combined with a lightweight horticultural oil (Sunspray)*. Researchers at Cornell University have discovered the fungicidal properties of this combination against powdery mildew on roses. Applications of one tablespoon baking soda plus 2.5 tablespoons of Sunspray oil in 1 gallon of water weekly are still experimental. Use it at your own risk.
- Another baking soda solution: mix a solution of 1 tablespoon of baking soda, 1 gallon of water, and a few drops of liquid soap, then spray it on affected leaves weekly.
- Weed Control: Baking soda can help control small weeds in garden paths or between paving stones. Sprinkle it directly on weeds to desiccate them and prevent regrowth. Here's an article about using baking soda for weed control.
- pH Adjustment for Alkaline-Loving Plants: Although not a primary method for changing soil pH, a small amount of baking soda can slightly raise soil pH for plants that prefer alkaline conditions, such as lavender and clematis.
Potential Downsides of Baking Soda
- Soil Imbalance: Baking soda is alkaline, and if used excessively, it can increase soil alkalinity, which can harm plants that prefer acidic or neutral soils. Over time, this can interfere with nutrient availability and negatively impact plant growth. Get a soil test before using baking soda in your garden.
- Leaf Burn: If not diluted properly, baking soda solutions can burn plant leaves, especially in strong sunlight. Always apply in the early morning or late afternoon and test a small section of the plant first.
- Build-Up in Soil: Baking soda does not break down quickly, so repeated use can lead to salt build-up in the soil, which may harm plant roots over time. Use it sparingly, and rinse the soil occasionally if using baking soda regularly.
While baking soda has some benefits in the garden, it should be used cautiously and sparingly to avoid long-term negative effects on soil and plant health.
*Sunspray is a horticultural oil designed to meet the growing need for an effective pesticide for those wary of putting potentially harmful chemicals into their gardens and the environment. Horticultural oil is for sale at big box stores and on Amazon.