Shuyang Zhen

Date of Award


Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)




Stephanie E. Burnett

Second Committee Member

Lois B. Stack

Third Committee Member

Michael E. Day


Greenhouse plant production relies on adequate water for irrigation as well as proper irrigation strategies to obtain high quality crops. Due to growing population and urbanization, competition and costs for available water are increasing. Growers are under pressure to operate more sustainably and reduce the amount of water used for production while maintaining plant quality. Precise irrigation based on plant water need not only allows for optimal plant growth but also conserves water and reduces pollutive fertilizer and pesticide runoff. Therefore, a thorough understanding of crop-specific water requirement is essential to use irrigation more efficiently.

Three investigations were conducted to determine water requirements of four popular perennials. All three investigations used a capacitance sensor automated irrigation system to accurately maintain substrate volumetric water content (ϴ = volume of water - volume of substrate) at constant levels. In the first study, rosemary (Rosmarinus officinalis), an aromatic perennial valued for its culinary and ornamental uses, was grown at one of eight 0 ranging from 0.05 to 0.40 L-L-1 to determine the optimal 0 for growing high quality and high-yield plants. In the second study, two popular herbaceous ornamentals, Canadian columbine (Aquilegia canadensis ‘Pink Lanterns’) and cheddar pink (Dianthus gratianopolitanus ‘Bath’s Pink’), were grown at one of nine 0 ranging from 0.05 to 0.45 L-L-1 to determine how ϴ affected their morphology and physiology. The third study assessed the influences of 0 on morphology, physiology, and cold hardiness of two English lavender cultivars (Lavandula angustifolia ‘Munstead’ and ‘Hidcote’), which are prized for their aromatic oils and attractive appearances, by growing plants at four different ϴ (0.1, 0.2, 0.3, or 0.4 L-L-1).

Growth of all four perennials was reduced at lower ϴ. Total leaf area and shoot fresh and dry weight of rosemary grown at ϴ > 0.20 L-L-1 were nearly twice or more than twice that of those grown at lower ϴ. Thus if crops will be harvested fresh, we recommend growing rosemary at ϴ > 0.20 L-L-1 to obtain high yield. Canadian columbine grown at ϴ of 0.30 L-L-1 had the highest quality (i.e. the greatest total leaf area and biomass production). Leaf area of cheddar pink grown at ϴ > 0.35 L-L1 was twice that of plants grown at the lowest ϴ; and highest shoot dry weight was observed at 0 of 0.35 L-L-1. Leaf-level net photosynthetic rate (AN) and stomatal conductance (gs) of Canadian columbine and cheddar pink were reduced at lower 0. For both English lavender ‘Munstead’ and ‘Hidcote’, plant height, width, inflorescence number, total leaf area and shoot dry weight increased with increasing ϴ. AN,gs, and transpiration (E) of ‘Munstead’ decreased with decreasing . ‘Munstead ϴ and ‘Hidcote’ grown at 0 of 0.1 L-L-1 had greater cold hardiness based on freezing-induced electrolyte leakage measurements. Water use efficiency (WUE = shoot dry weight + total amount of water applied per plant) of Canadian columbine and English lavender ‘Hidcote’ was not influenced by ϴ, while WUE of cheddar pink and English lavender ‘Munstead’ decreased at higher ϴ.