Root-zone heating for the winter production of greenhouse cut flower roses

© 2002 Dr. J. Kathleen MayotteThis thesis reports on root-zone heating for the production of cut flower roses in winter in a greenhouse. The production system is for short-stem roses, 300 to 400mm in length. Kardinal and Medeo cultivars were used. Each single-node rooted cutting is grown in bark-based medium in a tube and produces a single stem rose. An insulated, re-circulating ebb and flow bench heated with warm water was developed and evaluated as part of this research. The water that heated the root-zone also irrigated the crop. Root-zone temperature (RZT) could be maintained at a different temperature than the greenhouse air. The heated bench was tested in a cool room and in an unheated greenhouse to grow basil before being utilised with roses. The first rose experiment was in a growth chamber with an aerial temperature simulating winter conditions in an unheated greenhouse. Flower fresh weight was greater for both cultivars with root-zone temperature at 25° and 30°e. In the second rose experiment, an II-week trial, two aerial temperature environments were used in a greenhouse divided into 2 rooms. The air in one half of the greenhouse was heated to 200e both day and night and the other half was unheated. Supplementary lighting with high-pressure sodium (BPS) lights was used for the first 4 weeks. Kardinal roses in the heated greenhouse produce the heaviest flowers with 25°C RZT - as they did in the growth chamber trial. Medeo flower weight was not significantly affected by RZT nor was stem length for either rose. The Kardinal rose with RZT 25°C produced the thickest stems in both the heated and unheated environments. In the unheated greenhouse the Medeo rose with RZT 25°C also produced the thickest stems but they were only thicker than the stems produced at the ambient RZT. Stem diameter of Medeo in the heated environment was not significantly affected by RZT. Root-zone heating was assessed both as a substitution for, and as an enhancement to, conventionally heated (constant 200e air temperature) rose production. For the two cultivars studied, RZT at 25°C in an otherwise unheated greenhouse in winter produced a rose crop that was comparable in yield (both the number of flowering stems produced and their quality) to a rose crop grown in a conventionally heated environment. In the warm air greenhouse, RZT 25°C increased rose yield (number of flowers, diameter of stems and weight of flowers - but not stem length) for only the Kardinal rose. For the Medeo rose only the number of flowers produced was increased in the warm air greenhouse with RZT 30°C