We report a rapid (within 15 minutes), simple, green, inexpensive, versatile, and reproducible method for the synthesis of Ag triangular and hexagonal nanoplates in aqueous phase under ambient atmosphere. The method involves reducing silver oxide (Ag₂O) with hydrazine (N₂H₄) in the presence of trisodium citrate (TSC) and ethylenediaminetetraacetic acid disodium salt dihydrate (EDTA) in aqueous phase. In our system, TSC molecules serve as colloidal stabilizers to prevent as-prepared colloids from aggregating, while EDTA molecules serve as a ligand to monomers. The complexation of EDTA to Ag⁺ not only significantly slows the reduction kinetics of Ag⁺ by N₂H₄, but also kinetically controls the formation and growth of nanoplates. By varying the amount of EDTA, the shape (triangular and hexagonal) and edge length of nanoplates have been readily controlled, providing a surface plasmon resonance (SPR) response tunable from visible to near infrared. Most importantly, the SPR response is almost a linear function of the quantity of EDTA. Silver nanocrystals with a required SPR response can be provided, even without considering the actual nature of the Ag colloids. Recent results suggest that this chelation-mediated kinetic control over the sizes and morphologies of nanostructures can also be applied for other metal nanostructures.