Date of Award

2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Plant and Soil Science

First Advisor

Perry, Leonard

Abstract

Perennial growers overwintering plant stock require information to assist in deciding which containerized plants are most likely to successfully overwinter. Three studies on container-grown herbaceous perennials were conducted to examine the influence of plant age, soil moisture, and temperature cycling date on cold hardiness. In January, plants were exposed to controlled freezing temperatures of -2, -5, -8, -11, and -14C and then returned to a 3-5C greenhouse. In June, plants were assessed using a visual rating scale of 1-5 (1 = dead, 3-5 = increasing salable quality, varying by cultivar) and dry weights of new growth were determined. Controlled freezing in November and March were also included in the third study. In the first study, two ages of plants were exposed to controlled freezing temperatures in January. For Geranium x cantabrigiense 'Karmina', age had no effect on either rating or dry weight in one study year. In two Sedum 'Matrona' study years, age had no effect on dry weight but ratings were higher for older plants than younger plants in the first year and higher for younger plants than older plants in the second year. In two Leucanthemum x superbum 'Becky' study years, age had an effect on both rating and dry weight which were both generally higher for younger plants than older plants. In the second study, plants were maintained in pots at two different soil moisture levels prior to exposure to controlled freezing temperatures in January. Coreopsis 'Tequila Sunrise' and Carex morrowii 'Ice Dance' showed no effect on either rating or dry weight from soil moisture level. Soil moisture level had no effect on dry weight but ratings were higher for Geranium x cantabrigiense 'Cambridge' “wet” plants and for Heuchera 'Plum Pudding' “dry” plants. Carex laxiculmus 'Hobb' (Bunny Blue™) soil moisture level had an effect where dry weight was higher for “dry” plants. Means at were of salable quality for Geranium and Heuchera at all temperatures and Carex laxiculmus at temperatures above -11C. The effects of soil moisture level on Carex oshimensis were inconclusive. In the third study, during November, January, and March, plants were subjected to temperature cycling treatments prior to exposure to controlled freezing temperatures. Geranium x cantabrigiense 'Cambridge' were more tolerant of both temperature cycling and freezing temperatures in January and an increased number of cycles in November had an advantageous effect. Sedum 'Matrona' were more tolerant of temperature cycling and freezing temperatures in January and an increased number of cycles in March had an advantageous effect. Leucanthemum x superbum 'Becky' were more tolerant of temperature cycling in January in the second year of the study and an increased number of cycles in November had an advantageous effect in the first year and in all months in the second year. Overwintering younger container-grown plants is likely to result in more growth and higher quality following exposure to freezing temperatures. Effects of soil moisture level on overwintering container-grown plant growth and quality are cultivar-specific and a general effect could not be established in these studies. Overwintering container-grown plants are likely to be hardier in January and slight temperature cycles prior to exposure to freezing temperatures generally increase hardiness.

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