Red spruce seedlings growing in open top chambers in a nutrient-poor medium were exposed to mists containing one of five different combinations of H+, SO42-, NO3-, and NH4+ ions, three at pH 5.6 and two at pH 2.5. The mists were applied twice weekly from May until November, and the plants overwintered outdoors with no additional mist treatment. Seedlings that received mists containing sulphate (1.6 mol m-3) the previous growing season were more frost-hardy (i.e., their dehardening was delayed) the following April than seedlings that received lower concentrations of sulphate or none. Neither ammonium nor nitrate in the applied mist had any effect on dehardening, but they did advance budburst when applied together. In the presence of sulphate there was no effect of ammonium-N on the time of budburst. Exposure to mists containing nitrogen significantly increased the dry weight and length of the leading shoots that emerged from the buds and extended the following summer. There was no evidence that the stimulatory effects of nitrogen on growth made the seedlings less frost-hardy in spring.