Liquid-phase transmission electron microscopy (LP-TEM) enables one to directly visualize the formation of plasmonic nanoparticles and their postsynthetic modification, but the relative contributions of plasmonic hot electrons and radiolysis to metal precursor reduction remain unclear. Here we show silver deposition onto plasmonic gold nanorods (AuNRs) during LP-TEM is dominated by water radiolysis-induced chemical reduction. Silver was observed with LP-TEM to form bipyramidal shells at higher surfactant coverage and tip-preferential lobes at lower surfactant coverage. Ex situ silver photodeposition formed nanometer-thick shells on AuNRs with preferential deposition in inter-rod gaps, while chemical reduction deposited silver at AuNR tips at low surfactant coverage and formed pyramidal shells at higher surfactant coverage, consistent with LP-TEM. Silver deposition locations during LP-TEM were inconsistent with simulated near-field enhancement and hot electron generation hot spots. Collectively, the results indicate chemical reduction dominated during LP-TEM, indicating observation of plasmonic hot electron-induced photoreduction will necessitate suppression of radiolysis.