Many gardeners wonder what exactly organic gardening means. 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.
source = http://www.organicgardening.com/learn-and-grow/what-is-organic-gardening