There are times when even the most dedicated organic gardener is tempted to blast prize ornamentals with chemicals to slow the infuriating spread of fungal disease. But take heart -- fungal diseases like powdery mildew and black spot can be prevented, and sometimes destroyed, with environmentally friendly household products such as baking soda and liquid dish soap. Use the nontoxic spray on disease-prone ornamentals and edibles.
Preparing the Spray
Fill a bucket with 2 quarts of water. Warm water will help the baking soda dissolve more quickly, but cold water from a hose is fine.
Measure out 1 to 2 teaspoons of baking soda, and add it to the water. Follow with a few drops (about 1/2 teaspoon) of liquid soap. Liquid soap helps the spray adhere to plants and also has pest-fighting properties.
Stir the water well until the baking soda dissolves and the soap is evenly dispersed.
Pour the mixture into a spray bottle or a larger backpack sprayer. If you're using a spray bottle, a funnel helps channel the water though the bottle's narrow neck. A ladle or measuring cup with a spout also makes the decanting job a bit less awkward.
Spraying the Plants
Put on gardening gloves before spraying plants if your skin is sensitive. In general, baking soda and mild liquid soap are not considered caustic.
Spray plants thoroughly in late morning. This timing will give leaves a chance to dry before temperatures fall at night, which further decreases the risk of plant disease problems. Focus on the foliage when applying the spray. Coat both the upper and lower surfaces of leaves until the plants are dripping.
Refill the spray bottle or backpack sprayer with the remaining mixture in the bucket.
Apply the spray to plants every one to two weeks or after it rains. If the fungal disease is one that strikes during a certain season -- cold, wet springs are often risky when it comes to the spread of fungal spores -- use the spray primarily during that period.
Things You Will Need
- Measuring spoons
- Liquid dish soap
- Long-handled spoon
- Spray bottle or backpack sprayer
- Funnel (optional)
- Ladle or measuring cup with spout (optional)
- Gardening gloves (optional)
- Consider adding other ingredients to the basic baking soda formula to make it a more broad-spectrum spray. Instead of plain water, for example, you might infuse the water with a handful of chopped garlic (Allium sativum, U.S, Department of Agriculture plant hardiness zones 4 through 9), which has antifungal properties. Strain the garlic out of the water before adding the other ingredients. In addition, mixing in about 1/3 cup of vegetable oil per 2 quarts of water allows the baking soda spray to act as a barrier to fungal spores.
- Backpack-type sprayers are often designed so you can mix the formula directly in the sprayer. You may prefer doing this to premixing the ingredients in a bucket.
- If you find yourself with more baking soda spray than plants to spray, use the remaining liquid as a soil drench. The baking soda infusion may help eliminate or prevent soil-borne spores in the dirt around the plants.
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