Resting Period for Plants

Phases

• In the first stage of the dormancy process, pre-dormancy, the plant shuts down due to unfavorable conditions, such as low temperatures, but starts growing again if favorable conditions return. During the next phase, called true dormancy, the plant does not respond to intermittent favorable conditions and resumes growth only when when warm weather returns after cold temperatures have continued for a significant length of time. Typically, herbaceous plants stay in true dormancy longer than woody plants, such as trees. In the last phase, post-dormancy, the plant responds to positive environmental conditions with renewed growth.

Daylight

• The amount of daylight a plant receives triggers when it should go dormant. During a consistent period of shorter and shorter days, the plant prepares for dormancy by slowing its growth. A growth-regulating substance called abscisic acid appears to play a key role in the process, according to Virginia Tech. Scientists have found that the substance increases in plants as nights start to lengthen in autumn.

Temperatures

• Temperatures, another trigger for the dormancy period, work in combination with shortening days to signal the plant to slow down growth. The exact roles played by day length and temperatures in the dormancy process remain unclear. Some scientists believe only cold temperatures can trigger true dormancy, but this is unproven. It does appear, however, that cold temperatures, along with shorter days, quicken the pace of dormancy in many plants.

Dry Conditions

• Plants can go dormant in response to dry spells as well as winter conditions. For instance, turfgrass often turns brown during a drought, as a response to the lack of moisture. The grass conserves energy by only providing resources to certain parts of the plant. The grass does not enter a state of true dormancy but merely waits for the return of favorable conditions. When the amount of moisture the grass receives increases, growth resumes.