EXHIBIT 10.4

Exhibit 10.4

_________, 2026

Hydrofarm Holdings Group, Inc.

1510 Main Street

Shoemakersville, PA 19555

Re: Hydrofarm Holdings Group, Inc. - Lock-Up Agreement

Ladies and Gentlemen:

This Lock-Up Agreement is being delivered to you in connection with the Securities Purchase Agreement (the “Purchase Agreement”), dated as of October 27, 2026 by and among Hydrofarm Holdings Group, Inc. (the “Company”) and the investors who are parties thereto (the “Purchasers”), with respect to the issuance of (i) shares of common stock (the “Common Stock”) of the Company, par value $0.0001 per share, and/or pre-funded warrants in lieu thereof (the “Pre-funded Warrants”), which Pre-funded Warrants will be exercisable to purchase Common Stock and (ii) warrants (the “Common Warrants”) which Common Warrants will be exercisable to purchase Common Stock. Capitalized terms used herein and not otherwise defined herein shall have the respective meanings set forth in the Purchase Agreement.

In order to induce the the Company to enter into the Purchase Agreement, the undersigned agrees that, commencing on the date hereof and ending on the date that is one hundred twenty (120) days from the Effective Date (the “Lock-Up Period”), the undersigned will not, and will cause all affiliates (as defined in Rule 144 promulgated under the Securities Act) of the undersigned or any affiliate of the undersigned controlled by the undersigned not to, directly or indirectly (i) sell, offer to sell, contract or agree to sell, hypothecate, pledge, grant any option to purchase, make any short sale or otherwise dispose of or agree to dispose of, directly or indirectly, any Common Stock or Common Stock Equivalents, or establish or increase a put equivalent position or liquidate or decrease a call equivalent position within the meaning of Section 16 of the Exchange Act with respect to any Common Stock or Common Stock Equivalents owned directly by the undersigned (including holding as a custodian) or with respect to which the undersigned has beneficial ownership within the rules and regulations of the Commission (collectively, the “Undersigned's Shares”), or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of any of the Undersigned's Shares, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or other securities, in cash or otherwise, (iii) make any demand for or exercise any right or cause to be filed a registration statement, including any amendments thereto, with respect to the registration of any Common Stock or Common Stock Equivalents or (iv) publicly disclose the intention to do any of the foregoing.

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The foregoing restriction is expressly agreed to preclude the undersigned, and any affiliate of the undersigned and any person in privity with the undersigned or any affiliate of the undersigned, from engaging in any hedging or other transaction which is designed to or which reasonably could be expected to lead to or result in a sale or disposition of the Undersigned's Shares even if the Undersigned's Shares would be disposed of by someone other than the undersigned. Such prohibited hedging or other transactions would include, without limitation, any short sale or any purchase, sale or grant of any right (including, without limitation, any put or call option) with respect to any of the Undersigned's Shares or with respect to any security that includes, relates to, or derives any significant part of its value from the Undersigned's Shares.

Notwithstanding the foregoing, the undersigned may transfer the Undersigned's Shares (i) as a bona fide gift or gifts, provided that the donee or donees thereof agree to be bound in writing by the restrictions set forth herein; (ii) to any trust for the direct or indirect benefit of the undersigned or the immediate family of the undersigned, provided that the trustee of the trust agrees to be bound in writing by the restrictions set forth herein, and provided further that any such transfer shall not involve a disposition for value; (iii) to the Company (a) as forfeitures to satisfy tax withholding and remittance obligations of the undersigned in connection with the vesting or exercise of equity awards granted pursuant to the Company’s equity incentive plans, or (b) pursuant to a net exercise or cashless exercise by the undersigned of outstanding equity awards pursuant to the Company’s equity incentive plans; (iv) to any corporation, partnership, limited liability company or other business entity, all of the beneficial ownership interests of which are held exclusively by the undersigned, domestic partner and/or one or more family members of the undersigned or the undersigned’s domestic partner in a transaction not involving a disposition for value; (v) to one or more affiliates of the undersigned and distributions of securities to partners, members or shareholders of the undersigned; (vi) in transactions relating to Undersigned’s Shares acquired in open market transactions after the completion of the offering; provided that no filing under Section 16(a) of the Exchange Act shall be required or shall be voluntarily made in connection with subsequent sales of Undersigned’s Shares acquired in such open market transactions; (vii) for the establishment of a trading plan that complies with Rule 10b5-1 under the Exchange Act; provided,* however*, that the restrictions shall apply in full force to sales or other dispositions pursuant to such Rule 10b5-1 plan during the Lock-Up Period and no public announcement or disclosure of entry into such Rule 10b5-1 plan is made or required to be made, including any filing with the Commission under Section 13 or Section 16 of the Exchange Act; (viii) pursuant to a bona fide third party tender offer, merger, consolidation or other similar transaction made to all holders of Common Stock and involving a change of control; or (ix) by will, laws of intestacy or domestic relations orders; provided that in case of any transfer pursuant to clauses (i), (ii), (iii), (iv), and/or (v) above, each transferee, donee or distributee shall sign and deliver a lock-up letter substantially in the form of this Lock-Up Agreement, and provided further that such transfer shall not involve a disposition for value and such transfer is not required to be reported in any public report or filing with the Commission during the Lock-Up Period.

For purposes of this Lock-Up Agreement, “immediate family” shall mean any relationship by blood, marriage, domestic partnership or adoption, not more remote than first cousin. The undersigned now has, and, except as contemplated by the immediately preceding sentence, for the duration of this Lock-Up Agreement will have, good and marketable title to the Undersigned's Shares, free and clear of all liens, encumbrances, and claims whatsoever. The undersigned also agrees and consents to the entry of stop transfer instructions with the Transfer Agent against the transfer of the Undersigned's Shares except in compliance with the foregoing restrictions.

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In order to enforce this covenant, the Company shall impose irrevocable stop-transfer instructions preventing the Transfer Agent from effecting any actions in violation of this Lock-Up Agreement.

The undersigned acknowledges that the execution, delivery and performance of this Lock-Up Agreement is a material inducement to the Company to complete the transactions contemplated by the Purchase Agreement and that the Company shall be entitled to specific performance of the undersigned's obligations hereunder. The undersigned hereby represents that the undersigned has the power and authority to execute, deliver and perform this Lock-Up Agreement, that the undersigned has received adequate consideration therefor and that the undersigned will indirectly benefit from the closing of the transactions contemplated by the Purchase Agreement.

The undersigned understands and agrees that this Lock-Up Agreement is irrevocable and shall be binding upon the undersigned's heirs, legal representatives, successors, and assigns.

This Lock-Up Agreement may be executed in two counterparts, each of which shall be deemed an original but both of which shall be considered one and the same instrument.

This Lock-Up Agreement is intended for the benefit of the parties hereto and their respective successors and permitted assigns and is not for the benefit of, nor may any provisions hereof be enforced by, any other person or entity.

This Lock-Up Agreement will be governed by and construed in accordance with the laws of the State of New York, without giving effect to any choice of law or conflicting provision or rule (whether of the State of New York, or any other jurisdiction) that would cause the laws of any jurisdiction other than the State of New York to be applied. In furtherance of the foregoing, the internal laws of the State of New York will control the interpretation and construction of this Lock-Up Agreement, even if under such jurisdiction's choice of law or conflict of law analysis, the substantive law of some other jurisdiction would ordinarily apply.

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Agreed to and Acknowledged:

HYDROFARM HOLDINGS GROUP, INC.

By: _______________________

Name:

Title: