Neem oil spray can repel and kill garden insect pests while also treating fungal plant diseases. Available in small bottles for home use, pure neem oil must be mixed with water so that the oil makes up no more than 2 percent of the garden spray. A few drops of mild liquid soap, such as nondetergent dish soap, helps the spray stick to plants.
Fill a 1-quart bucket with warm water. Add about 1/8 teaspoon of liquid soap and mix the water vigorously to disperse the soap.
Drizzle in 1 teaspoon of neem oil slowly while continuing to stir the soapy water. This will result in a 0.5 percent neem solution, which is useful for preventative spraying.
Unscrew the top of a spray bottle. Put a funnel over the neck of the bottle and pour the neem solution into it, until the liquid is almost to the neck of the bottle. Screw the spray head back onto the bottle.
Shake the bottle after filling it.
Spray plant leaves thoroughly on both their tops and bottoms -- especially the latter, where pests and eggs often lurk.
Refill the bottle as needed from the remaining neem oil pesticide in the bucket. If you don't use the entire amount in one day, discard the remainder of the spray. Drenching the ground around infested or diseased plants is a useful way of using up the extra neem solution.