Industrial Hemp Farming Act of 2013 - Amends the Controlled Substances Act to exclude industrial hemp from the definition of "marihuana." Defines "industrial hemp" to mean the plant Cannabis sativa L. and any part of such plant, whether growing or not, with a delta-nine tetrahydrocannabinol concentration of not more than 0.3 percent on a dry weight basis. Deems Cannabis sativa L. to meet that concentration limit if a person grows or processes it for purposes of making industrial hemp in accordance with state law, unless the Attorney General determines that the state law is not reasonably calculated to comply with such definition.