Microscopic dust particles may be formed by accretion of neutral or positively charged precursors in laboratory plasmas. When the concentration of neutral precursors is large, as when a mixture of He and CO is discharged, the radius of grains increases linearly with time andexsituelectron microscopy shows polydisperse particle sizes. By contrast, when the particle acquires multiple negative charges to satisfy the floating potential and the grain size is less than the plasma’s linearized Debye length, ionic growth increases the radii of the particles ast1/3. Monodisperse particle size distributions consistent with ionic growth kinetics are observed in low pressure He plasmas excited by graphite electrodes.