The 2012 ASHS Annual Conference

Temperature is one of the most important climate factors in greenhouse ornamental cultivation since it not only affects plant growth rates, quality and time of production cycle but also heating costs. It has been known that proper root zone heating could reduce energy consumption without compromising plant growth & quality. However, there has been little research on the interaction between root zone heating and air temperature management in ornamental crop production. Since the highest heating energy use usually occurs during the pre-morning or early morning periods, temperature regimes with temperature drop during pre-morning and/or early morning periods could reduce energy use. In this study, three growth chamber trials were conducted to investigate the response of poinsettia, one of the most important ornamental crops in North America, to various temperature regimes with temperature drops at the same daily integrated temperature and their interactions with root zone heating for conserving energy while ensuring crop quality. Four air temperature treatments (one in each growth chamber): 1) Control; 2) PM2 (with 2-h pre-morning low temperature of 13 °C); 3) PM4 (with 4-h pre-morning low temperature of 13 °C); and 4) PMM2 (with 2-h pre-morning and 2-h early morning low temperature of 13 °C) were applied to poinsettia plants from the appearance of first color until anthesis. The air temperatures in other periods during a 24-h period were adjusted accordingly so that the four treatments had the same daily integrated temperature. Four root zone temperatures (20, 23.3, 26.7, and 30 °C) were applied inside each of the air temperature treatments for 16 hours (18:00 to 10:00). It was found that the air temperature treatment with pre-morning temperature of 13 °C (PM4) seemed only marginally affected plant growth and higher root zone temperature could be used with the treatment, which indicates a good potential for energy savings without compromising plant growth and quality.