It takes one season. Any non genetically modified crops grown on a USDA certified organic farm the seed would be certified organic. The rules are a certified organization must use organic certified seed if available. Not all varieties of seed are availble organnically, so non-organic seed can be used as long as the seed is not treated with any prohibited substance or process and not Genetically altered. The grower must provide records of the variety ,seed source,and places where attempts have been made to find organic seed for that variety. I know this because I am in the process of having my farm certified organic. I grow seed of varieties (Heirlooms)that are not certified organic. I grow them to get the seed certified organic.My greenhouses are also certified so all my vegetable starts are certified organic which is another requirement for a grower. All annual plants must come from a certified organic source and there is no exception for this rule. So if the grower wants to grow cherokee purple tomatoes he has to grow his own plants from organic seed or buy plants from a certified organic grower such as myself. If he wants to grow a variety that there is no organic source of plants for he can not buy uncertified plants but he can grow his own plants from seed but the seed must be certified and if there is no source for certified seed of that variety then he can use seed that is not chemically treated or processed and the grower must have this approved by the certifying agent. This only applies to annual crops for perrenial crops such as apples asparagus etc the plants must be from a certified organization if the variety is not availble organically then just as with the seed the grower can buy unorganic plants that are not chemically treated or genetically modified and these plants have to be grown organically on a certified organic farm for one complete season before they are considered organic. Have I completly confused you now? Rodger

Thanks, Rodger, and no, you haven't confused me!

I was curious about the steps required for organic certification, and it looks like a lot of recordkeeping, paperwork, and inspections, but the requirement about using "organic" seed led me to the question about what a grower would do if there weren't any available. Could you essentially grow your own from non-organic seeds?

You're saying you can use the very next batch of seeds from plants grown organically for growing certified organic crops, selling the seeds under an organic label, and offering starts from the seeds under an organic label.

Again, thanks for satisfying my curiosity.

Your understanding is 100% correct. Rodger

Last I checked (and sometimes it is different for different certifying agencies), if you've checked three sources that normally sell organic seed and can't find the variety you want in the quantity you need, then you can buy seed that is not organic and sell the produce that results as organic.
For instance if you are looking for XYZ variety of beans, and need 5 pounds of it, and have not found this quantity in organic seed, then you can buy a 5 pound bag of untreated seed (and obviously non-GMO) to grow and sell at market as organic as long as you grow it in organic soil using organic methods. If the companies have 3 ounce packages of the specific variety and it is organic, you are not required to buy 5 pounds worth of 3 ounce packages.
Check with the certifying agency which you will be working with down the line, to clarify things.

anniew

Good heavens! Thirty-six states have 55 agencies for organic certifications, California with the most. See the link below.

The standards for certification are apparently outlined in the National Organic Program. Wonder if the state standards vary any?

Here is a link that might be useful: Accredited Certifying Agents by State