How Plants Prepare for Dormancy: The Science of Fall

By Michael Chen · October 4, 2026

Dormancy: A Survival Strategy Millions of Years Old

Plant dormancy is not simply "sleeping"—it's an active, hormonally controlled process that allows plants to survive freezing temperatures, drought, and reduced light. Understanding the biochemistry behind dormancy helps gardeners work with natural rhythms rather than against them.

The Hormonal Trigger: Abscisic Acid

As daylight shortens in autumn, plants increase production of abscisic acid (ABA), often called the "stress hormone." ABA signals growth points to stop dividing, initiates the formation of protective bud scales, and triggers the breakdown of chlorophyll in leaves. It's the chemical messenger that says "winter is coming—shut down non-essential operations."

How Plants Sense Day Length

Plants use a pigment called phytochrome to measure the ratio of red to far-red light, which changes as days shorten. This photoperiodic response is remarkably precise—many species initiate dormancy preparation when day length drops below a species-specific threshold, often within a window of just a few days year after year.

Chlorophyll Breakdown and Color Change

Green chlorophyll masks other pigments that are present in leaves year-round. When chlorophyll production stops in fall, these hidden pigments become visible:

Carotenoids (yellows and oranges): Always present, revealed when green fades
Anthocyanins (reds and purples): Actively produced in fall as a photoprotective "sunscreen" during nutrient recovery
Tannins (browns): Waste products that remain after all useful compounds are withdrawn

Carbohydrate Storage: Banking Energy for Spring

Before dropping leaves, trees actively withdraw sugars, amino acids, and minerals from leaf tissue and transport them to roots and woody tissue for storage. This is why premature leaf removal (raking too early) can deprive trees of nutrients they haven't finished recovering.

Root Growth Continues Underground

While above-ground growth stops, root systems continue growing through fall and even into mild winters. This is why fall is the ideal time to plant trees and shrubs—they focus energy on root establishment rather than top growth.