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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2021-10-15</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001477246</issuerCik>
        <issuerName>S&amp;W Seed Co</issuerName>
        <issuerTradingSymbol>SANW</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001074749</rptOwnerCik>
            <rptOwnerName>MFP PARTNERS LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O MFP INVESTORS LLC</rptOwnerStreet1>
            <rptOwnerStreet2>909 THIRD AVENUE, 33RD FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>See remarks below</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001105685</rptOwnerCik>
            <rptOwnerName>MFP INVESTORS LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>909 THIRD AVENUE, 33RD FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>See remarks below</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000918537</rptOwnerCik>
            <rptOwnerName>PRICE MICHAEL F</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O MFP INVESTORS LLC</rptOwnerStreet1>
            <rptOwnerStreet2>909 THIRD AVENUE, 33RD FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>See remarks below</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $0.01 per share</value>
            </securityTitle>
            <transactionDate>
                <value>2021-10-15</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1391941</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>2.73</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>17442726</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">This report is filed jointly by MFP Partners, L.P. (&quot;MFP Partners&quot;), MFP Investors LLC (&quot;MFP Investors&quot;) and Michael F. Price (each, a &quot;Reporting Person&quot; and, collectively, the &quot;Reporting Persons&quot;) in connection with their respective direct and indirect relationships with S&amp;W Seed Company (the &quot;Company&quot;).  MFP Investors is the general partner of MFP Partners.  Mr. Price is the managing partner of MFP Partners and the managing member and controlling person of MFP Investors.</footnote>
        <footnote id="F2">MFP Partners is the direct beneficial owner of the shares of common stock of the Company (&quot;Common Stock&quot;) reported herein.  Each Reporting Person other than MFP Partners may be deemed to be the indirect beneficial owner of such shares of Common Stock; however, each such Reporting Person disclaims beneficial ownership of such shares of Common Stock except to the extent of such Reporting Person's pecuniary interest therein, and this report shall not be deemed an admission that any of these Reporting Persons is the beneficial owner of the shares of Common Stock described herein for purposes of Section 16 of the Securities Exchange Act of 1934 or for any other purpose.</footnote>
    </footnotes>

    <remarks>Mr. Alexander C. Matina (Vice President, Investments at MFP Investors), serves as a member of the board of directors of the Company as a nominee of MFP.  Each of MFP Partners, MFP Investors and Mr. Price may be deemed a director of the Company by deputization on the basis of the relationships among such persons and Mr. Matina.</remarks>

    <ownerSignature>
        <signatureName>MFP PARTNERS, L.P., By: MFP INVESTORS LLC, By: /s/ Michael F. Price, Name: Michael F. Price, Title: Managing Member</signatureName>
        <signatureDate>2021-10-18</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>MFP INVESTORS LLC, By: /s/ Michael F. Price, Name: Michael F. Price, Title: Managing Member</signatureName>
        <signatureDate>2021-10-18</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Michael F. Price</signatureName>
        <signatureDate>2021-10-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
