Growing Small Farms Act of 2013 - Amends the Internal Revenue Code, with respect to the liability of employers of agricultural labor for federal unemployment tax under the Federal Unemployment Tax Act (FUTA), to increase from $20,000 or more to $40,000 or more the amount of wages which such employers must pay in a calendar quarter for agricultural labor before being treated as employers for FUTA purposes. Provides for an inflation adjustment to such increased wage threshold after 2014.