Four Phases of Dormancy for Douglas-Fir

(cold hardiness or acclimation)

1. Dormancy induction: Period from mid-July to late September when winter- resting bud are initiated and develop in response to moderate moisture stress. Excessive watering or nitrogen at this time may interfere with this process.
    
2. Dormancy deepening: Period from September to mid-November when buds are well formed and metabolic changes slowly induce frost hardiness. Seedlings are still susceptible to damage from desiccation or hard freezing. Short photo-periods and mild temperatures are required to complete this phase. The seedlings will not resume growth in response to favorable conditions. The metabolic changes or freezing mechanisms include:
   a. Decrease starch and increase sugar.
   b. Lower overall plant water.
   c. Low "in cell water" and high "outside cell water"
   d. Outside cell water freezes first giving off heat that protects in cell. (When water freezes it releases heat--80 calories per gram of water)
    
3. Dormant: Period from November to March when seedlings have maximum resistance to environmental stress. Seedlings require a minimum time span of below 40 degrees Fahrenheit temperature to complete this phase and cannot resume growth. (Time required varies for different species; for example, Douglas-fir takes at least six weeks.) If a chinook starts plant out, it can still regain dormancy if refrozen slowly, but a quick freeze is what does damage.
    
4. Post-dormancy: Period from thawing out to bud burst. Seedlings gradually lose their resistance to frost damage and other environmental stress. The length of this transition phase depends upon temperature and photo-period; the more favorable the conditions for growth, the sooner buds will burst.

< Back to Transportation, Care, and Storage of Seedlings; and Planting

Last Modified: 07/05/2007