Phosphorus Deficiency

Purple or reddish pigmentation on stems and petioles, with older leaves looking dull, dark or bronze before browning and dropping. Be careful: many strains naturally show purple stems regardless of P status, especially in cool nights, so confirm with feed history and growth slowdown rather than colour alone.

What usually causes it

• Cold root zone (below ~15-18 C) - the most common cause indoors, locks out P even when present
• pH below 5.5 or above 7.5 (P most available 6.0-7.0 in soil, 5.8-6.3 in coco/hydro)
• Insufficient P in the working solution during pre-flower / stretch
• Overwatered, anaerobic root zone

Related product categories

• Base Nutrients
• PK Boosters
• Root Stimulators & Beneficials

Terms worth knowing

• pH

Walk the questions if you are not sure this is the match. The notes above are the same ones the tool ends on.