Place 2 tbsp. of rubbing alcohol in a spray bottle filled with 1/2 cup of water. Spray your basil plants with a light mist of this solution. The rubbing alcohol can ward off some pests without harming plants.
Rinse aphids off of basil plants with a garden hose. The National Gardening Association recommends doing this if you notice aphids lingering on your plants. Using the force of water from a hose washes away some pests without harming the plant.
Add 5 or more inches of additional compost, manure, fertilizer or another type of organic matter to the soil. Johnny's Selected Seeds website recommends increasing organic matter in the soil because it favors pathogen reduction.
Move potted basil plants in door before summer begins because garden pests such as Japanese beetles like to feed on basil during this time.
Spray basil plants with Azadiractin pest control spray if your natural pest control efforts don't work. Natural pest control can eliminate all or most pests, but persistent insects may come back.