If you want to have a truly organic garden, you will need to buy organic seeds. Plants raised from any other type of seed are not truly organic, even if you have never used pesticide or weed killer in your garden. Standard seeds may have been subject to all kinds of sprays while they were forming on the parent plant.
In addition, non organic seeds could even be genetically modified. Genetically modified or engineered plants have had their genes altered to encourage them to have certain qualities, such as disease resistance, higher productivity, sweeter taste, etc.
This is different from selective breeding and hybridization which has been going on for centuries in order to produce the vegetables and fruits that we have today. With genetic modification, there is no way of knowing what else might be altered when the genetic material is tampered with. Even an apparently beneficial alteration such as making a plant more resistant to disease can have a negative effect if this means that bacteria evolve to survive. There is a risk that human diseases could become increasingly resistant to antibiotics as a result. There is also a risk of harming biodiversity and perhaps producing new allergens or even new diseases.
If you try to shop locally for organic seeds you may find there is not much choice available in your local stores. Of course this varies according to where you live. Some people are lucky enough to live close to a good nursery with a large range of organic plants and seeds.
However, even if you do have trouble finding organic seeds in your local area, there is no problem because you have a huge choice on the internet. As more and more gardeners and agriculturalists are turning to organic gardening methods, more organic seeds become available. Not only can you now get them for most every type of vegetable that you would want to grow in your garden, but in many cases you even have the choice of several different varieties of each plant.
Ordering online is ideal because being so small and light, seeds are very cheap to ship. You can have a large order and still pay very low shipping charges.
The most popular organic seeds are for vegetables that will be grown for food. This is not surprising. People who grow items to eat do not want to have them contaminated with pesticides and weed killers even before they are planted. In a flower garden, while purists may still want to choose organic, it is more likely that people will buy regular seeds and simply avoid using environmentally unfriendly products on the growing plants. But for anything that will be going onto your table, organic seeds are best.