Prospectus Filed Pursuant to Rule 424(b)(3) (424b3)

Filed pursuant to Rule 424(b)(3)

Registration No. 333-256938

PROSPECTUS SUPPLEMENT NO. 15

(to Prospectus dated June 16, 2021)

Hydrofarm Holdings Group, Inc.

3,369,138 Shares of Common stock

This prospectus supplement supplements the prospectus dated June 16, 2021 (the “Prospectus”), which forms a part of our registration statement on Form S-1 (No. 333-256938). This prospectus supplement is being filed to update and supplement the information in the Prospectus with the information contained in our Current Report on Form 8-K, filed with the Securities and Exchange Commission on June 23, 2022 (the “Current Report”). Accordingly, we have attached the Current Report to this prospectus supplement.

The Prospectus and this prospectus supplement relates to the offer and sale from time to time of up to 3,369,138 shares of our common stock by the selling stockholders listed on page 26 of the Prospectus. The number of shares offered for sale by the selling stockholders consists of up to 3,369,138 shares of our common stock currently issuable upon the exercise of warrants held by the selling stockholders, which were issued in connection with a private placement of units, each consisting of a share of common stock and a warrant to purchase an additional one-half (1/2) share of common stock, which concluded on October 30, 2018. The shares of our common stock offered hereby are issuable upon the exercise of warrants issued by us in a series of private placement transactions completed prior to the filing of the registration statement containing the Prospectus.

Our common stock is traded on The Nasdaq Global Select Market under the symbol “HYFM.” On June 22, 2022, the closing price of our common stock was $4.09 per share.

Investing in our common stock is highly speculative and involves a high degree of risk. See “Risk Factors” beginning on page 21 of the Prospectus to read about factors you should consider before buying shares of our common stock.

Neither the Securities and Exchange Commission nor any other regulatory body has approved or disapproved of these securities or passed upon the accuracy or adequacy of the disclosures in the Prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus supplement is June 23, 2022.

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): June 22, 2022

Hydrofarm Holdings Group, Inc.

(Exact name of registrant as specified in its charter)

Delaware

001-39773

81-4895761

(State or other jurisdiction of
incorporation or organization)

(Commission
File Number)

(I.R.S. Employer
Identification No.)

1510 Main Street

Shoemakersville, PA 19526

(Address of Principal Executive

Offices) (Zip Code)

Registrant’s telephone number, including area code: (707) 765-9990

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligations of the registrant under any of the following provisions:

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:


Title of each class	Trading symbol(s)	Name of each exchange on which registered
Common Stock, $0.0001 par value per share	HYFM	NASDAQ Global Select Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ¨

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ¨

Item 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

(b) Departure of President

On June 22, 2022, Hydrofarm Holdings Group, Inc. (the “Company”) and Mr. Terence Fitch, the Company’s President, mutually agreed to Mr. Fitch’s departure as President, effective June 24, 2022.

Item 7.01 Regulation FD Disclosure

On June 23, 2022, the Company issued a press release announcing Mr. Fitch’s resignation. A copy of the press release is attached as Exhibit 99.1 and incorporated herein by reference.

The information in this Item 7.01 of this Current Report on Form 8-K and Exhibit 99.1 attached hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended. The information contained in this Item 7.01 and in the press release attached as Exhibit 99.1 to this Current Report on Form 8-K shall not be incorporated by reference into any filing with the Securities and Exchange Commission made by the Company, whether made before or after the date hereof, regardless of any general incorporation language in such filing.

Item 9.01 Financial Statements and Exhibits.


Exhibit No.						Description

99.1						Press Release, dated June 2 3 , 2022.
104						Cover Page Interactive Data File (embedded within the Inline XBRL document).

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.