<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-02-04</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000825542</issuerCik>
        <issuerName>SCOTTS MIRACLE-GRO CO</issuerName>
        <issuerTradingSymbol>SMG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001083206</rptOwnerCik>
            <rptOwnerName>DONALD ARNOLD W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O THE SCOTTS MIRACLE-GRO COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>14111 SCOTTSLAWN ROAD</rptOwnerStreet2>
            <rptOwnerCity>MARYSVILLE</rptOwnerCity>
            <rptOwnerState>OH</rptOwnerState>
            <rptOwnerZipCode>43041</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Deferred Stock Units</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2008-02-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>2765</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>2765</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2765</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The deferred stock units were granted, together with an equal number of related dividend equivalents, under The Scotts Miracle-Gro Company Amended and Restated 2006 Long-Term Incentive Plan (the &quot;2006 Plan&quot;).</footnote>
        <footnote id="F2">Each whole deferred stock unit represents a contingent right to receive one common share of The Scotts Miracle-Gro Company.  Each dividend equivalent represents the right to receive additional deferred stock units in respect of dividends that are declared and paid during the period beginning on the grant date and ending on the settlement date with respect to the common share represented by the related deferred stock unit.</footnote>
        <footnote id="F3">The deferred stock units will become 100% vested on February 4, 2011, subject to earlier vesting or forfeiture in accordance with the terms of the award agreement.  Subject to the terms of the 2006 Plan, vested deferred stock units will be settled in a lump sum as soon as administratively practicable, but no later than 90 days, following the earliest to occur of:  (i) the reporting person's cessation of service as a director of The Scotts Miracle-Gro Company; (ii) the reporting person's death; (iii) the date the reporting person becomes totally disabled; or (iv) the fifth anniversary of the grant date (February 4, 2013).</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Kathy L. Uttley as attorney-in-fact for Arnold W. Donald</signatureName>
        <signatureDate>2008-02-06</signatureDate>
    </ownerSignature>
</ownershipDocument>
