To make a big batch of concentrate for future use, drop a whole bar of neem soap into a wide mouth gallon container. Fill that jug with 1 gallon very hot tap water and let sit a week, stirring daily. If you don’t have a wide-mouthed jar, you can soak the soap in a quart of hot water four times, pouring the mixture that fits into a regular gallon container.
You’ll end up with 1 gallon of a thick soap concentrate that keeps just about forever in a lidded container. To make a batch of spray, dissolve 1 cup of this concentrate in 1 gallon warm water, shake, then pour it into your sprayer. Thus a cheap bar of soap will make you SIXTEEN GALLONS of a very safe and effective fungicide and insecticide that won’t harm the environment nor make your vegetables and flowers and herbs toxic.
How does it work? The soap alkalinizes the leaf surface, but powdery mildew and black spot and sooty mold ( on citrus and gardenias) fungi need an ACIDIC leaf cuticle to grow onâ€¦plus as a soap it helps to rinse them off. Spray UP at the undersides of the leaves if you are after blackspot fungus on roses.