Make your own garden pest soap by mixing 1 tablespoon of regular dish soap with 1 quart of water. Multiple quarts of water require an equal number of tablespoons of dish soap, so a gallon of garden pest soap requires about 4 quarts of water and 4 tablespoons of soap. Only use regular dish soap made for hand-washing dishes when making garden pest soap, as dishwasher detergent is too harsh for use on plants.
After mixing your dish soap and water, transfer the liquid to a clean spray bottle. If reusing an old spray bottle, make sure it is totally clean before adding the soap, as many cleaners and other household products are harmful to plants.
While many dish soaps are safe for use in the garden, some plants may have a negative reaction to certain brands. Test your garden pest soap by spraying it on a few leaves, waiting an entire day and then checking those leaves. If the leaves wilt, become discolored or are otherwise unhealthy, consider using a different brand of dish soap.
Garden pest soaps work by breaking down fatty acids in insect exoskeletons. This is the same property that gives dish soaps their degreasing properties. When fatty acids in an insect's exoskeleton break down, it loses moisture and eventually dehydrates. Garden pest soaps are especially effective at controlling aphids, leaf miners, spittle bugs and other small insects, but they are less harmful toward bees, butterflies and other beneficial insects.