Effect of Overwintering Environment on the Survival of 30 Species of Herbaceous Perennials

Abstract

Abstract There is increased interest in overwintering containerized perennials. However, there is little information available on overwintering success. The objective of this research was to determine overwinter survival and regrowth quality of 30 perennial species hardy in USDA zones 3, 4, or 5. Three overwintering treatments were used for each species: unprotected containers outside, containers in an unheated building, or in the ground. On April 16, 2004, and May 17, 2004, following overwintering, plant quality, plant height and flowering time were evaluated. Twenty-one species were successfully overwintered in an unheated building and 13 of those had quality ratings equal to or higher than those overwintered in-ground. Ceratostigma plumbaginoides, Kniphofia Pfitzer's Hybrid, Leucanthemum ×superbum ‘Snowcap’, and Stokesia laevis ‘Honeysong Purple’ rated significantly higher when overwintered in containers stored inside than in the ground. Flowering time and height measurement differences were not significant. Coreopsis ‘Limerock Ruby’, Diascia integerrima CoralCanyon™ and Gaura lindheimeri ‘Siskiyou Pink’ did not survive in any treatment. None of the species tested, with the exception of Sedum ‘Matrona’, survived when overwintered unprotected outside. Overwintering certain species of containerized perennials inside an unheated building such as a garage is a viable option for homeowners to improve survival.