Evaluation of Structureless Overwintering Systems for Container-Grown Herbaceous Perennials

Abstract Five structureless overwintering systems were evaluated for temperature moderation and protection of 18 container-grown herbaceous perennials from low-temperature injury. Two light-excluding treatments; 30 cm (1 ft) of straw between two layers of 4-mil white polyethylene and 18 cm (7 in) deep, in-ground beds protected with one layer of 4-mil white polyethylene and 30 cm (1 ft) of woodchips, provided the greatest moderation of winter low and early spring high temperatures, but also resulted in severe etiolation. A bonded white polyethylene/microfoam overwintering blanket (thermoblanket) with translucent properties provided comparable plant survival percentages despite dramatic temperature extremes recorded beneath this cover and, in late winter, created an environment conducive to moderate plant growth without formation of etiolated tissue.