Good harvests, along with plants that resist disease and pests, are the byproducts of building healthy soil. Soil-building methods have been used for centuries. Compost, garbage, hay, straw, manure, and crops high in nitrogen that are grown just to be turned under are high on the list of natural fertilizers. Rotating the location of crops is also a practice used in organic gardening to prevent disease and pests from lingering on in the soil to attack the next season's crops. The individual gardener, working on a small scale, has little trouble adopting organic gardening techniques.
Chemical pesticides have no place in organic gardening.
Organic gardeners have many insecticides at their disposal. Some are derived from plants, such as pyrethrum and neem. Some of the best insect killers are simply a refined kinds of soap or oil. And others more subtly pit one kind of organism against the pest. Often these pesticides are chosen for exactly the opposite reason that people choose other kinds of insecticides.