UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): December 21, 2012

THE MOSAIC COMPANY

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (800) 918-8270

Not applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

Item 8.01. Other Events.

On December 21, 2012, Louisiana Economic Development issued a press release announcing a potential ammonia plant at The Mosaic Company’s existing Faustina site in Louisiana, a copy of which is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

The press release attached hereto as Exhibit 99.1. contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Such statements include, but are not limited to, statements about future financial and operating results. Such statements are based upon the current beliefs and expectations of The Mosaic Company’s management and are subject to significant risks and uncertainties. These risks and uncertainties include but are not limited to the predictability and volatility of, and customer expectations about, agriculture, fertilizer, raw material, energy and transportation markets that are subject to competitive and other pressures and economic and credit market conditions; the level of inventories in the distribution channels for crop nutrients; changes in foreign currency and exchange rates; international trade risks; changes in government policy; changes in environmental and other governmental regulation, including greenhouse gas regulation, implementation of the U.S. Environmental Protection Agency’s numeric water quality standards for the discharge of nutrients into Florida waterways or possible efforts to reduce the flow of excess nutrients into the Mississippi River Basin or the Gulf of Mexico; further developments in judicial or administrative proceedings; difficulties or delays in receiving, increased costs of or challenges to necessary governmental permits or approvals or increased financial assurance requirements; resolution of global tax audit activity; the effectiveness of the Company’s processes for managing its strategic priorities; adverse weather conditions affecting operations including in Central Florida or the Gulf Coast of the United States and including potential hurricanes, excess rainfall or drought; actual costs of various items differing from management’s current estimates, including, among others, asset retirement, environmental remediation, reclamation or other environmental regulation, or Canadian resources taxes and royalties; accidents and other disruptions involving Mosaic’s operations, including brine inflows at its Esterhazy, Saskatchewan potash mine and other potential mine fires, floods, explosions, seismic events or releases of hazardous or volatile chemicals, as well as other risks and uncertainties reported from time to time in The Mosaic Company’s reports filed with the Securities and Exchange Commission. Actual results may differ from those set forth in the forward-looking statements.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits.

Reference is made to the Exhibit Index hereto with respect to the exhibit furnished herewith.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

EXHIBIT INDEX