The simple answer is that organic gardeners don't use synthetic fertilizers or pesticides on their plants. But gardening organically is much more than what you don't do. When you garden organically, you think of your plants as part of a whole system within Nature that starts in the soil and includes the water supply, people, wildlife and even insects. An organic gardener strives to work in harmony with natural systems and to minimize and continually replenish any resources the garden consumes. Organic gardening, then, begins with attention to the soil. You regularly add organic matter to the soil, using locally available resources wherever possible. And everyone has access to the raw ingredients of organic matter, because your lawn, garden and kitchen produce them everyday. Decaying plant wastes, such as grass clippings, fall leaves and vegetable scraps from your kitchen, are the building blocks of compost, the ideal organic matter for your garden soil. If you add compost to your soil, you're already well on your way to raising a beautiful, healthy garden organically.
The other key to growing organically is to choose plants suited to the site. Plants adapted to your climate and conditions are better able to grow without a lot of attention or input; on the other hand, when you try to grow a plant that is not right for your site, you will probably have to boost its natural defenses to keep it healthy and productive.
One of the greatest arguments among gardeners comes in the area of fertilization. Some prefer totally natural materials; others are content with manufactured fertilizers; many use a combination of both. In some cases, the selection is based on economics. Often, the availability of organic materials is limited when large quantities are needed.
For plant growth, both forms of fertilizer can be equally effective. Organisms in the soil break down organic materials to form inorganic compounds identical to those in many commercial fertilizers. Plants are unable to determine a difference in the original source of the compounds they absorb. Extra growth often is a response to better root environments and action of soil organisms working on the organic matter.
While some materials, such as manure, add organic matter as well as fertility, other organic fertilizers are not suppliers of organic matter. One of the major benefits of organic fertilizers is that they break down slowly and are less likely to release nutrients rapidly enough to burn plant roots if used in large amounts.
Many inorganic fertilizers are more soluble and can burn plants if used improperly. Since many organic materials break down slowly, they supply nutrients to plants for a much longer period of time without frequent applications. Because they are not quickly soluble, they are not leached from the soil during heavy rains and, therefore, are more continuously effective. Some organic fertilizers also contain micronutrients.
The availability of nutrients from organic fertilizers depends on their breakdown by soil organisms, which in turn depends on weather and soil conditions. Release of nutrients is much slower when the soil is cool or heavily saturated with water. Also, breakdown slows during drought unless soil is irrigated or heavily mulched to keep in soil moisture and keep temperature more constant. Where you need a quick fertilizer response, inorganic fertilizers tend to provide it. Many of the organics have a fertilization lag. Their nutrients are not available to plants until the organic matter has decomposed.