When winter's first frost abruptly ends summer's bounty, hardy perennials, such as hostas, appear to die. Actually, they only die down to soil level -- to the tops of their thick, stringy roots. The cycle of growth, flowering, death and dormancy is one of the keys to the perennials' ability to live for long numbers of years.
Annuals and Perennials
Annuals and perennials approach life differently. Annuals grow fast, flower until they produce enough seeds to reproduce themselves successfully, then die. Since the odds are against one seed successfully producing a new plant, they flower early and, if the gardener deadheads flowers before seed can set, they will flower until frost kills them. Perennials such as hostas grow more slowly and flower only during certain periods. In addition to gathering the energy to flower, they develop tubers, crowns or other specialised roots that allow them to reproduce vegetatively. Hostas grow thick roots during the winter to support groups of buds that will form new plants.
Unlike woody shrubs and trees, branches of herbaceous perennials contain so much water that they freeze when weather turns cold. Dormancy is a strategy that perennials have evolved to survive in areas where winter temperatures fall below freezing. Perennials in temperate areas die back to their crowns or roots for a period of rest. This habit gives hosta roots a chance to develop without having to support luxuriant top growth and the plant's insignificant but numerous flowers.
Hostas are hardy over a wide area, but seem to perform better in their northern range than in the South. The key is that many perennials, including hostas, require a period of chilling to produce flowers the following year. In order to chill roots, air temperature must drop below freezing and the top of the plant must die back to the ground. Experiments at Auburn University in 1998, established that lack of chilling resulted in delayed emergence in spring, stress, and weakened plants. Two commonly planted cultivars, Hosta fortunei "Francee" and H. sieboldiana "Frances Williams", performed best when kept for a period of six to eight weeks at 3.89 degrees Celsius. Longer periods resulted in slightly earlier emergence. The Auburn study was done for nurseries in U.S. Department of Agriculture zone 8 that had experienced an unusually mild winter and slow starts in their hosta stocks.
Hostas are hardy perennials: dying back to the ground is an essential survival behaviour. Hostas have genes that control growth, flowering and dormancy. The length of daylight signals each plant when to initiate each step in its seasonal growth. Even tender perennials, evergreens and tropical plants have dormant periods but hardy perennials' sense of what day it is based on the length of the day signals their roots to switch to dormant mode before cold weather might kill the entire plant.
- Purdue University Extension; Growing Perennial Flowers; Michael N. Dana, et al.; 2003
- Auburn University Agriculture; Chilling Effects on Shoot Emergence and Subsequent Growth in Hosta; Gary J. Keever, et al.
- Global Gardens; Hosta Physiology; Robert M. Solberg; 1996
- Global Gardens; Photoperiodism in Hostas; Jim Hawes