Fabric Containers Enhance Survival of Selected Over-Wintered Nursery Stock

Field observations prior to 2004 indicated that nursery stock growing in fabric above-ground containers may have higher survival rates than that growing in plastic containers, when exposed to cold events. During the winter of 2004-05, four species of shrubs were left in the container nursery without winter protection in Durham NH (zone 5b) and differences in survival and spring growth due to container type were confirmed. Since then, ten species representing a range of cold hardiness ratings have been screened in multi-year trials for survival and growth responses associated with container type. Plants over-wintered in situ were compared to controls over-wintered in traditional covered piles. Physocarpus opulifolius, Potentilla fruticosa, Potentilla parvifolia, and Stephanandra incisa survived and grew normally regardless of container type or treatment. Itea virginica and Ilex x meserveae were completely winter-killed in both exposed container types, surviving only in protected piles. Fabric containers resulted in reduced mortality rates for four species (Viburnum plicatum tomentosum, Viburnum trilobum, Weigela florida, Cornus sericea), compared with plastic containers in situ. These plants represent zone 2 - 5 hardiness ratings, indicating lack of correlation between root cold tolerance and shoot hardiness. Although there was no difference in mean root zone temperatures during the coldest months of 2007-09, minimum temperatures averaged 4^◦ C lower in exposed plastic than in fabric containers.