High pH-induced Iron Deficiency of Fall Garden Mums
Fall garden mums should be grown with a substrate pH range of 5.8 to 6.2. Substrate pH influences nutrient availability and uptake, therefore use recommended 1:2 Extraction, SME, or PourThru methods to determine and monitor substrate pH and soluble salt [referred to as electrical conductivity (EC)] values. High substrate pH above 6.5 can inhibit iron (Fe) uptake causing newly developed leaves to become deficient in Fe and display interveinal chlorosis (yellowing). If plants become severely Fe-deficient, interveinal chlorosis intensifies and leaves become completely chlorotic or bleached (white). Corrective procedures for high substrate pH should begin within the range of 6.3 to 6.5 but be careful not to lower the substrate pH too low. Corrective actions for lowering high substrate pH include: (1) switching to an acidic-base fertilizer; (2) acid water drenches; or (3) iron chelate applications.
W. Garrett OwenAssistant Professor and Greenhouse Extension Specialist , University of Kentucky
W. Garrett Owen is an Assistant Professor and Extension Specialist of floriculture, greenhouse and controlled-environment crop production in the Department of Horticulture at the University of Kentucky. He has an appointment in research, teaching and Extension. His area of expertise is controlled environment specialty crop production; plant nutrition; plant growth regulation; and production problem diagnostics.