Fertilizer concentration affects growth and flowering of subirrigated petunias and begonias

Nitrate pollution and water conservation are two of the most important environmental concerns for greenhouse growers. Closed irrigation systems, such as ebb and flow, can minimize these problems, The objective of this study was to determine optimal fertilizer concentrations for petunia (Petunia x hybrida Hort, Vilm-Andr,) and begonia (Begonia x semperflorens-cultorum Hort,) grown with ebb-and-flow irrigation. 'Ambassador Scarlet' begonia and 'Dreams Mix' petunia were grown as bedding plants in three soilless media. Plants were fertilized with solutions of a 20N-4.4P-16.6K water-soluble fertilizer with electrical conductivities (EC) of 0.15, 0.6, 1.2, 1.8, 2.4, or 3.0 dS.m(-1). Maximum growth occurred with a fertilizer EC of 2.2 dS.m(-1) for petunia and 1.6 dS.m(-1) for begonia, Petunia growth was best in the medium with the highest porosity (Metro-A3ix 220), but choice of medium had little effect on begonia growth. Leachate EC and pH were determined throughout the experiment, using the pour-through method, Leachate EC rose with increasing fertilizer concentration, and increased over time. The pH of the leachate decreased with increasing fertilizer concentration and dropped 0.5 to 1 unit over the course of the experiment with the higher fertilizer concentrations (greater than or equal to0.6 dS.m(-1)). Plant growth was not very sensitive to Leachate EC, Begonia and petunia grew well when the EC at the end of the production cycle was between 1.7 to 6.1 and 2.1 and 5.4 dS.m(-1), respectively.