Plant Dormancy: How Plants Rest in Winter

By Marcus Williams · October 18, 2026

What Is Plant Dormancy?

Dormancy is a state of suspended or dramatically slowed growth that allows plants to survive unfavorable conditions, primarily winter cold and drought. Unlike death, dormancy is reversible — the plant remains alive but inactive, conserving energy and protecting vulnerable tissues until conditions improve. Dormancy occurs in seeds, buds, roots, and entire plants.

Endodormancy vs. Ecodormancy

Endodormancy is internally controlled — even if you bring a dormant branch into a warm greenhouse, it will not grow until it has accumulated sufficient chilling hours. Ecodormancy is externally controlled — the plant is ready to grow but waits for warm temperatures. Trees must satisfy their chilling requirement (typically 600 to 1,500 hours below 45°F) before transitioning from endodormancy to ecodormancy.

The Role of Abscisic Acid

Abscisic acid (ABA) is the primary hormone that induces and maintains dormancy. As days shorten in autumn, ABA levels rise in buds and stems, inhibiting cell division and elongation. Growth-promoting hormones like gibberellins and auxins decrease. The balance between ABA and growth hormones determines whether a bud remains dormant or breaks into growth.

Cold Hardening

Before entering full dormancy, plants undergo cold hardening — a gradual process triggered by shortening days and cooling temperatures. During hardening, cells accumulate sugars and amino acids that act as natural antifreeze, lowering the freezing point of cell contents. Cell membranes become more flexible to withstand ice crystal formation in intercellular spaces.

Supercooling in Buds

Some buds can supercool — keeping water in a liquid state well below its normal freezing point. Peach and cherry flower buds can supercool to minus 20°F without forming ice crystals. If ice does nucleate inside supercooled tissues, the rapid crystallization kills the cells. This is why sudden cold snaps are more damaging than gradual cooling — there is no time for controlled dehydration.

Dehydration Tolerance

During deep dormancy, many woody plants lose up to 50 percent of their cell water to extracellular ice. The remaining cell contents become highly concentrated with sugars and proteins, preventing further freezing. This controlled dehydration is fundamentally different from drought stress — the plant orchestrates it as a survival strategy rather than suffering it as damage.

Breaking Dormancy in Spring

As temperatures warm and days lengthen, ABA levels decline and gibberellins increase. Buds swell as cells rehydrate and begin dividing. The timing of bud break varies by species and is influenced by accumulated growing degree days. Early-breaking species like maples and forsythia are more vulnerable to late frosts than later-breaking species like oaks and ash.

Climate Change and Dormancy Disruption

Warmer winters reduce chilling hour accumulation, causing delayed or irregular bud break in fruit trees. Some species break dormancy earlier, increasing vulnerability to spring frosts. Researchers are breeding fruit varieties with lower chilling requirements to adapt to warming climates. Understanding dormancy physiology is critical for predicting how forests and orchards will respond to changing conditions.