How Plant Dormancy Works: The Science

By Michael Chen · October 8, 2026

Dormancy Is Not Death

Dormancy is an active survival strategy, not passive shutdown. Plants produce hormones (abscisic acid) that suppress growth and trigger cold-hardening processes. Cells accumulate sugars that act as antifreeze, lowering the freezing point of cell sap to -20°F or lower in some species.

Endodormancy vs Ecodormancy

Endodormancy is internal — the plant will not grow even if conditions are perfect. It requires a specific number of chilling hours (temperatures between 32-45°F) to break. Ecodormancy is external — the plant is ready to grow but waits for warm temperatures. This two-phase system prevents plants from breaking bud during a warm January spell.

Chilling Hours and Why They Matter

Apple trees need 500-1,000 chilling hours. Peaches need 200-1,000 depending on variety. If a plant does not accumulate enough chill hours, it blooms erratically, produces fewer leaves, and yields poorly. This is why southern gardeners must choose low-chill varieties.

Cold Acclimation Process

In fall, decreasing daylight triggers cold acclimation. First, plants stop growing and move sugars to roots and stems. Then cell membranes change composition — more unsaturated fatty acids keep membranes flexible in cold. Finally, cells produce dehydrins — proteins that protect cell structures from ice crystal damage.

De-Acclimation Risk in Late Winter

Warm spells in February-March cause plants to de-acclimate — they lose cold hardiness. A plant hardy to -20°F in January may be damaged at 10°F after a warm week. This is why late winter warm spells followed by freezes cause the most damage to landscape plants.

Breaking Dormancy in Spring

Once chilling requirements are met, plants need heat accumulation (growing degree days) to break ecodormancy. Different species use different base temperatures — apples use 40°F, grapes use 50°F. When enough heat units accumulate, buds swell and growth resumes.