By James Feucht, PhD, Colorado State University Cooperative Extension
Dormancy in Northern Hemisphere plants is caused by chemical changes within plant cells. It is stimulated by cooling temperatures and shorter days in late summer and fall. This "binds" water so it cannot freeze and injure plant cells. To break dormancy, plants must first go through a period of cold (about 40 degrees F or colder) for an average of 63 days. This cold period triggers changes which, when warm weather appears, allows plants to "deharden" and resume growth.
Photo: Judy Sedbrook
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010