The growth of ZnO nanoparticles from zinc acetate in propanol proceeds by coarsening. The driving force for this process is the increase in equilibrium solubility with decreasing particle size, described by the Gibbs-Thompson equation. We show that the growth rate, and hence particle size, can be controlled by injection of capping ligands that adsorb onto the particle surface, Both thiols and phosphonic acids are shown to slow the growth rate of ZnO nanoparticles, indicating that they adsorb onto the particle surface and provide a barrier to further dissolution.