Date of Award


Degree Type


Degree Name

Master of Science (MS)


Horticulture and Landscape Architecture

First Advisor

Roberto G. Lopez

Committee Chair

Roberto G. Lopez

Committee Member 1

Neil S. Mattson

Committee Member 2

Cary A. Mitchell


Given the high energy costs for greenhouse floriculture production, growers are constantly searching for more energy-efficient methods of production. For example, some growers will lower greenhouse air temperature set points or grow crops in unheated high tunnels (HTs) or outdoors in order to minimize or eliminate heating costs. Unfortunately, development can be delayed and morphology can be altered if the mean daily air temperature (MDT) is reduced. We proposed that reducing MDT in combination with root-zone heating (RZH) could be an energy-efficient method for producing high-quality floriculture crops without significant delays. Unheated HT and unprotected outdoor production are very low-cost systems for bedding plant production, but little information is available on crop developmental and morphological effects. The objectives of this study were, therefore, to quantify growth and development of 1) red poinsettia cultivars finished under reduced MDT in combination with RZH (Experiment 1); 2) several petunia cultivars and recombinant inbred lines grown under reduced MDT in combination with RZH (Experiment 2); and 3) cold-tolerant and cold-intermediate annual bedding plants grown in an unheated HT or unprotected outdoor growing area with or without an acclimation period (Experiment 3). In Experiments 1 and 2, time to flower decreased with increasing root-zone temperature across species and cultivars. Overall, high-quality poinsettias can be produced without delay if MDT is reduced by 5 °C, but a RZH set point of ≥24 °C is employed during the finish stage. Similarly, MDT can be reduced to 15 °C for petunia production when a RZH set point of 27 °C is utilized. In Experiment 3, flowering of all species was delayed when plants were grown outdoors compared to in the HT. However, high-quality annual bedding plants could be produced outdoors, depending on species, given the increased daily light integral (DLI) and air movement to keep plants compact. When plants were given a one-week acclimation period in the HT prior to outdoor production, almost all species were delayed less than 1 week compared to those grown in the HT only. When producing crops outdoors, growers must be aware of the risk of delay or crop loss due to extreme weather. Generally, high-quality floriculture crops can be produced with minimized cost for heating in a greenhouse with reduced MDT in combination with RZH, as well as in an unheated HT or outdoors, depending on species and weather conditions.

Included in

Horticulture Commons