Environmental concerns surround the use of plant growth retardants (PGRs) for plant height control. Studies suggest that plant height control may be achievable through modifications in plant nutrition. The primary objective of this study was to evaluate an alternative means of plant height control through adjustments the ratios of the three macroelements: N, P and K. Ratios of NO3-/NH4+, NO3-/H2PO4-, NO3-/K+, K+/H2PO4-, NH4+/H2PO4- and NH4+/K+ were tested at different levels, and approximately 50 hydroponic nutrient solutions were compared to quantify their effects on plant height of 3 species, namely marigolds, sunflowers and tomatoes. Solutions were tested at an electrical conductivity (EC) of ~1.2mS·cm-1 in the first objective, and retested at four ECs (0.6, 1.2, 2.2 and 4.0mS·cm-1) in a second objective. Marigold height decreased while tomato height increased with increasing EC. Responses to ratio modifications were largely season and species dependent, suggesting that modifications in plant nutrition may not effectively control plant height in certain hydroponic systems. The Canadian Ornamental Horticulture Alliance(COHA), Flowers Canada (Ontario), Ontario Ministry of Agriculture Food and Rural Affairs (OMAFRA), Agriculture Canada (Growing Forward), Vineland Research and Innovation Center (VRIC)