Truths or myths, fact or fiction, setting the record straight concerning nitrogen effects on levels of frost hardiness

•Findings of positive effects of N for plant frost hardiness exceeded the negative findings.•The effect depends markedly on the season.•In general, the positive effects occurred in autumn and the negative effects in spring. Approx. 50 papers (found from Scopus) published since 1990 were reviewed to determine whether or not nitrogen additions benefit frost hardiness in some plant species. The results varied according to species, timing of the effect, nitrogen source and plant tissue concentration. The key finding is that in 40% of reported cases nitrogen supply increased frost hardiness, while in 29% of cases nitrogen had no effect on frost hardiness. Together these findings comprise 69%, implying that in the majority of cases nitrogen additions are not deleterious but actually improve frost hardiness, especially in autumn.