A fish waste/hemlock-fi r sawdust compost (FWC) was evaluated as a container growth medium and N source for the greenhouse production of marigold (Tagetes patula `Queen Sophia') and geranium (Pelargonium xhortorum `Sprinter Scarlet') in 10-cm containers. Treatments were a factorial set of three Douglasfir bark (B)/three FWC mixtures (100% FWC; 50% FWC/50% B; 100% B) and three rates of N fertilizer (0, 300 and 600 ppm N) applied every 2 weeks. After the initial irrigation, plants were drip-irrigated to negate leaching from the containers.
Weekly measurements of leachate conductivity, pH, and inorganic N were made on additional replications of the 0-ppm N plants in all growing media. Plant height and width were measured at 2-week intervals and, at the end of the production cycle, flower number, shoot fresh and dry weight, visual quality, and root dry weight were measured. The growing medium by N interaction was significant for all variables. Results indicated that plants receiving 0 ppm N in 100% FWC were larger and of higher quality than plants in 100% B receiving 600 ppm N. In 100% FWC, marigold shoot growth, dry weight, and quality were not influenced by N rate. The observed geranium and marigold growth response indicated that FWC was an effective N source and growing medium when leaching was minimized with drip irrigation.