Generally, CNG producers must use seed that is organically grown, whether CNG, Certified Organic, or uncertified whenever they are available. But, if a producer is unable to find the variety they need in organically grown form after checking with at least three suppliers, CNG allows an exception for a farmer to use conventionally grown seed, just as long as it is not chemically treated or genetically engineered. This same rule applies to seed potatoes, onion sets, and sweet potato slips.