Herbaceous plants grown in decorative containers in a northern United States summer season have traditionally consisted of annual and tropical species. There has been an increasing trend in residential landscaping to utilize perennials along with annuals and tropicals in mixed containers. With this increased use comes an increased interest in overwintering perennials for use the following year. The objective of this research was to evaluate the survivability and quality of 30 perennial species with a USDA hardiness rating of zone 3, 4, or 5. Perennials were selected based on length of bloom, foliage interest, and architectural form. Three overwintering treatments were used: containers left outside, containers overwintered in an un-heated building, or plants overwintered in the ground. Perennials were transplanted on June 16, 2003 in Columbus, Ohio (USDA Hardiness Zone 5b). Plant quality, plant height and flowering time were recorded on April 16, 2004 and May 17, 2004. Twenty-one species were successfully overwintered inside the un-heated building. Thirteen species in the container treatment overwintered inside were rated equal to or higher than the in ground treatment. Ceratostigma plumbaginoides, Kniphofia Pfitzer’s Hybrid, Leucanthemum xsuperbum ‘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 Coral Canyon™ and Gaura lindheimeri ‘Siskiyou Pink’ did not survive in any treatment. None of the species tested, with the exception of Sedum ‘Matrona’, survived the outside container treatment. Overwintering certain species of perennials inside an unheated building such as an unheated garage is a viable option for homeowners to improve survival.
Species used were: Alchemilla mollis ‘Thriller’, Anemone tomentosa ‘Robustissima’, Calamagrostis xacutiflora ‘Overdam’, Ceratostigma plumbaginoides, Coreopsis ‘Limerock Ruby’, Crocosmia xcrocosmiiflora ‘Lucifer’, Diascia integerrima Coral Canyon™, Epimedium xrubrum, Euphorbia amygdaloides var. robbiae, Gaura lindheimeri ‘Siskiyou Pink’, Geranium sanguineum ‘Alpenglow’, Heuchera americana ‘Palace Purple’, Heuchera sanguinea ‘Splendens’, Hosta ‘Francee’, Hosta ‘June’, Hypericum calycinum, Kniphofia Pfitzer’s Hybrid, Lamiastrum galeobdolon ‘Variegatum’, Lamium maculatum ‘Anne Greenway’, Lavendula angustifolia ‘Munstead’, Leucanthemum xsuperbum ‘Snowcap’, Nepeta xfaassenii ‘Dropmore’, Panicum virgatum ‘Shenandoah’, Phlox paniculata ‘Mt. Fuji’, Scabiosa caucasica ‘Butterfly Blue’, Sedum ‘Matrona’, Stachys byzantina ‘Big Ears’, Stokesia laevis ‘Honeysong Purple’, Thymus serphyllum ‘Annie Hall’, Veronica alpina ‘Alba’.