The 2012 ASHS Annual Conference

Urban sprawl has caused increased water usage and expanded water quality issues. Salt water intrusion and dropping aquifers are major concerns in the ornamental industry. Bedding plant production is dependent on good water quality and suitable nursery medium. High alkalinity irrigation gradually increases medium pH and Na, and often requires a decrease in lime rate to maintain a slightly acidic medium. The objective of this study was to determine the optimum medium Ca and Mg rate and source in greenhouse production using a moderately alkaline water source. Petunia plugs were planted into medium filled jumbo six trays. Plants were fertigated daily with a balanced soluble fertilizer six days a week using a moderately alkaline water source. Media treatments consisted of a 60% pinebark:40% perlite mixture amended with either no amendments (control), dolomitic lime (2lbs/cubic yard), gypsum+slow release epsom salt (2+2lbs/cubic yard), dolomitic lime (4 lbs/cubic yard), dolomitic lime (2lbs/cubic yard)+gypsum+slow release epsom salt (2+2lbs/cubic yard), gypsum+slow release epsom salt (4+4lbs/cubic yard), dolomitic lime (4lbs/cubic yard)+gypsum+slow release epsom salt (4+4lbs/cubic yard), dolomitic lime (4lbs/cubic yard)+gypsum+slow release epsom salt (2+1lbs/cubic yard), dolomitic lime (4lbs/cubic yard)+gypsum+slow release epsom salt (2+2lbs/cubic yard). Plant growth, dry weight and color resulted in significant differences among treatments and sources. Interveinal chlorosis was evident in the control and low rates of Ca and Mg especially after 6 weeks. Plant growth measurements and dry weights indicated a decrease in growth with low Ca rates. Overall growth differences did occur for both source and rate of Ca and Mg. If rate of lime is decreased due to increasing medium pH, supplemental Ca and Mg applications may be beneficial.