Cover - shares	9 Months Ended
	Sep. 30, 2021	Nov. 02, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-39773
Entity Registrant Name	Hydrofarm Holdings Group, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	81-4895761
Entity Address, Address Line One	270 Canal Road
Entity Address, City or Town	Fairless Hills
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	19030
City Area Code	707
Local Phone Number	765-9990
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	HYFM
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		44,519,302
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001695295
Current Fiscal Year End Date	--12-31