Current research•Greenhouse crops
Evaluate and determine fresh yield of approximately 15 species and cultivars of lettuces, greens and herbs for seasonal production in Kentucky tobacco greenhouses
Robert G. Anderson, Deptartment of Horticulture
Lettuces, greens and herbs are specialty crops for specialty markets. These crops may be quickly adaptable to the float beds common in tobacco greenhouses. In response to grower interest and the rapidly expanding market for organic produce, relatively soluble organic fertilizers were evaluated for the growth of Bibb and Grand Rapids lettuces in float beds in the spring and fall of 2000.
Plants were grown in plastic souffle cups (50 ml) with holes cut in the bottom. These cups were placed into holes (plant density of 35 m-2) in polystyrene sheets (2.5 x 85 x 120 cm) and the sheets were allowed to float on the water surface of the float bed. Commercial organic fertilizers derived from fish waste (Mermaid's Fish Powder, GreenAll Fish Emulsion), digested seaweed (Algamin, EcoNutrients), bat guano and a formulated organic fertilizer (Omega, from bonemeal, bloodmeal and rock phosphate) were compared to a standard inorganic fertilizer, 16-2-10 N-P-K maintained in the water 1.2 mS cm-1. Dissolved oxygen was maintained at a minimum of 4 ppm in all treatments. Lettuce (‘Ostinata', ‘Diamond Gem', ‘Red Sails', ‘Oakleaf') fresh and dry weights were determined after 4 weeks of fertilizer treatment. Weekly water analyses determined available NO3, NH4, P, K, Ca, Mg, Fe, S, B, Mn, Zn, Mo, pH, EC, and alkalinity.
Organic fertilizers did not produce plants comparable to the inorganic fertilizer control during the 4 week production period. Fish waste and digested seaweed were of little value for lettuce production. Commercial quality lettuce could be produced in bat guano and the formulated fertilizer but would require 10 to 20 days longer than inorganic fertilizer.
The high organic content of the fish waste dramatically reduced available oxygen in the water, so the lettuce roots could not grow in the water. Overall nutrient content of the fish waste products was low to moderate and very low in the digested seaweed. These fertilizers offer only limited hope for commercial production.
Nutrient levels in the bat guano and formulated fertilizer solutions were comparable or higher than the inorganic fertilizer. These fertilizers are good sources of nitrate so the lettuce grew reasonably well.
These preliminary studies demonstrated that significant additional work is necessary to develop a system to utilize organic fertilizers for greenhouse production of lettuce in float beds. A formulated fertilizer seems to be the best approach to the development of a reliable nutrient solution. The Omega fertilizer was a good start, but had too much P which caused Ca and Mg deficiencies. The nutrient solution should be monitored constantly, but it would require a great deal of work to determine what additions can stabilize the nutrient levels and pH. Plus these additives must meet organic certifications standards. There appeared to be lettuce variety responses to the fertilizers and the float bed system, so many varieties would have to be evaluated. In addition, visual differences in disease infection occurred between the fertilizer treatments used.
Utilize the bedding plants grown during the spring for plant evaluation trials
Annual and perennial garden flowers were evaluated at the Horticulture Research Farm (Lexington) and demonstrated at the University of Kentucky Arboretum (Lexington), Louisville Zoo (Louisville), UK Research and Education Center (Princeton) and Purchase Area Master Gardener Demonstration Garden (Paducah).
Six to twenty plants of each variety or species were lined out in rows to evaluate performance where maintenance is less intense. We concentrated more on all varieties or species of the same genus at the Research Farm and on a few plants of many types at the demonstration sites.
In the summer of 2000, we evaluated 28 cultivars of vegetative verbena, 15 cultivars of lantana, 5 cultivars of calibrachoa, 4 cultivars of bacopa, 6 cultivars of calla, Dragon Wing begonia, Profusion Zinnias, gazanias in the annual flower trial. In the perennial trials we concentrated on daisies, or composites, with asters, coneflowers, rudbeckia, chrysanthemum, stokesia and others, plus 5 types of salvia, 6 types of veronica, nepeta, and some native ornamental grasses.
The annual trials demonstrated that the vegetative verbenas primarily derived from V. canadensis were much superior to those derived primarily from V. tenuisecta. The ‘Temari' series and ‘Temari Patio Blue', in particular, were the best performers for Kentucky gardens. The V. tenuisecta cultivars produce few flowers from July to late August, but are spectacular in spring and fall. Lantana and Calibrachoa cultivars plus ‘Dragon Wing' begonia and ‘Profusion' zinnias were excellent for Kentucky landscapes. Calla, bacopa and gazania had only moderate performance. The perennials will be evaluated for two more seasons before recommendations are made.
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