Improving the water and energy efficiency of food production is an important part of a sustainable future. Indoor plant environments have the potential to greatly improve crop yields and to nearly close the water cycle of crops as long as excess humidity can be efficiently managed and recycled for irrigation. In this study, we introduce the novel concept of using fertilizer as a liquid desiccant to dehumidify indoor plant environments and recover valuable water vapor for irrigation. The proposed process circulates liquid fertilizer through membrane contactors, across which water vapor is drawn from the humid plant environment, driven by the low vapor pressure of the highly concentrated fertilizer. As water is collected by the fertilizer, and the solution is sufficiently diluted, it can then be supplied directly to the crops as a clean water and nutrient source. This study provides a theoretical analysis of several common single solute fertilizers, from which calcium nitrate and diammonium phosphate are identified as having particular promise. In addition, a laboratory test bench and experimental methods are described, and preliminary experimental results are presented, providing the first-ever proof-of-concept demonstration of fertilizer dehumidification. Pathways for future research and development are discussed.