A 3 year study was initiated to evaluate the survival of several species of container-grown herbaceous perennials with various overwintering techniques. Although species reacted individually to overwintering covers, those with white reflective surfaces generally provided adequate protection. Straw, non-reflective Plantfoamss™, or no cover usually resulted in large losses. Container medium temperatures were 4° to 7°C (8° to 15°F) degrees warmer than surrounding air temperatures, with a “sandwich” of 30 cm (1 ft ) fluffed oat straw between layers of white polyfilm providing the least medium temperature fluctuation (3°C or 6°F with ambient fluctuation of 16°C or 34°F), and the most temperature moderation (1°C or 34°F with ambient −16°C or 3°F). Uncovering plants later than the first week in April occasionall y resulted in plant losses.

cold hardiness, cold protection, microfoam
Yarrow (Achillea filipendulina Lam. ‘Parker's Variety’), Wallflower (Cheiranthus Cheiri L. ‘Apricot Delight’), Shasta daisy (Chrysanthemum × superbum Bergmans ex J. Ingram ‘Alaska’), Larkspur (Delphinium elatum L. ‘Blue Fountains’), Pink (Dianthus L. ‘Double Sonate Mix’), Baby's-breath (Gypsophila paniculata L. ‘Double Snowflake’), Coralbells (Heuchera sanguinea Engelm. ‘Bressingham Hybrids’), Coralbells (Heuchera L. ‘Firesprite’), Lavender (Lavandula angustifolia Mill.).
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Author notes

Research supported by the Vermont Agricultural Experiment Station, University of Vermont, Burlington. Hatch Project VT-398. Appreciation is expressed to the Vermont Plantsmen Association and the New England Greenhouse Conference for partial funding of this project; and to Nancy Rowan, Karen Alpert and Ann Hazelrigg for technical assistance.

2Associate Professor.

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1990