When should you buy conventionally grown lemons instead of organic? It's simple: If you plan on using the zest of a lemon -- the outside skin or peel -- always go with organically grown citrus. But if you're just using the juice of the lemon, it's OK to go with conventionally grown. Even with a good washing, pesticide buildup and waxes on the outside can make it tough to remove all of the chemicals before you zest a lemon. Organic lemons are grown without pesticides, so the zest is safe to use for cooking. But even with organic, be sure you wash it well: Lemons -- conventional and organic -- are touched by many hands before reaching your supermarket.