SEGMENT INFORMATION - Net Sales by Product Category (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Revenue from External Customer [Line Items]
Net sales	$ 3,551.3	$ 3,924.1	$ 4,925.0
U.S. Consumer | Growing media and mulch
Revenue from External Customer [Line Items]
Net sales	1,223.7	1,192.6	1,286.7
U.S. Consumer | Lawn care
Revenue from External Customer [Line Items]
Net sales	897.4	973.6	1,060.6
U.S. Consumer | Controls
Revenue from External Customer [Line Items]
Net sales	362.9	382.2	402.4
U.S. Consumer | Roundup marketing agreement
Revenue from External Customer [Line Items]
Net sales	138.7	132.3	145.2
U.S. Consumer | Other, primarily gardening
Revenue from External Customer [Line Items]
Net sales	221.0	248.1	302.8
Hawthorne
Revenue from External Customer [Line Items]
Net sales	467.3	716.2	1,424.2
Hawthorne | Lighting
Revenue from External Customer [Line Items]
Net sales	165.9	200.0	452.4
Hawthorne | Nutrients
Revenue from External Customer [Line Items]
Net sales	105.3	148.0	324.7
Hawthorne | Growing environment
Revenue from External Customer [Line Items]
Net sales	72.5	143.7	264.0
Hawthorne | Growing media
Revenue from External Customer [Line Items]
Net sales	67.5	119.0	192.6
Hawthorne | Other, primarily hardware
Revenue from External Customer [Line Items]
Net sales	56.1	105.5	190.5
Other
Revenue from External Customer [Line Items]
Net sales	240.3	279.1	303.1
Other | Lawn care
Revenue from External Customer [Line Items]
Net sales	75.8	92.9	99.2
Other | Growing media
Revenue from External Customer [Line Items]
Net sales	93.0	96.6	116.7
Other | Other, primarily gardening and controls
Revenue from External Customer [Line Items]
Net sales	$ 71.5	$ 89.6	$ 87.2