Controversy surrounds the impact of atmospheric nitrogen (N) deposition on frost hardiness. There are no specific field studies and the relevance of data from N fertilizer studies is questionable. Field N manipulation experiments with Norway spruce [Picea abies. (L) Karst.] at Skogaby, Sweden, and Sitka spruce [P. sitchensis. (Bong.) Carr.] at Aber in Wales and Deepsyke in Scotland were sampled in November/December to assess hardiness. The N was supplied with different accompanying ions, from 35 to 100 kg N ha−1 yr−1, as solid fertilizer, in irrigation water or to the canopy. Detached shoots were experimentally frozen and damage was assessed from electrolyte leakage. Frost hardiness was not significantly affected by the N treatments irrespective of site, dose, species or length of treatment. Shoots that had received N were generally the most hardy. The results are consistent with the nutritional status of the foliage at the time of sampling.