Potassium bicarbonate is a natural fungicide which is often used for organic gardening. Chemically, the compound is similar to common baking soda, (sodium bicarbonate), but the sodium is replaced with potassium, which is gentler on plants.
Potassium bicarbonate can be purchased least expensively at garden and hardware stores, but is also available at pharmacies and wine-making supply shops. The compound is also sold under various brand names, such as GreenCure.
Measure the surface area of the garden to be sprayed in square feet.
Calculate the amount of potassium bicarbonate that will be needed to spray the garden. One gallon of water mixed with 4 teaspoons of potassium bicarbonate will treat an area approximately 10-by-10 feet. Potassium bicarbonate is typically sold by the pound. There are 768 teaspoons in one pound, so one pound of potassium bicarbonate is enough to prepare 192 gallons of spray (768 divided by 4 teaspoons per gallon = 192 gallons.
Buy potassium bicarbonate at garden centers, hardware stores, from a pharmacy or at a wine-making supply shop. If you buy it from a pharmacy or wine shop, the potassium bicarbonate will be sold in ounces, typically 2-ounce bottles. There are 6 teaspoons in 2 ounces of sodium bicarbonate, so a single 2-ounce bottle can be used to make 3 gallons of spray.