Dormancy in plants is a period of temporarily suspended growth that allows a plant to survive unfavorable conditions like winter cold, drought, or nutrient scarcity. Rather than a shutdown, it’s a highly regulated survival strategy. Plants don’t simply stop growing because conditions are bad. They actively prepare for dormancy weeks or months in advance, producing protective compounds, relocating nutrients, and altering their hormone balance to ensure they can resume growth when conditions improve.
Three Types of Plant Dormancy
Plant scientists classify dormancy into three categories based on where the growth-suppressing signal originates. Understanding these distinctions helps explain why a seemingly healthy plant isn’t growing, whether it’s a tree bud in winter, a seed in soil, or a branch shaded by the canopy above.
Endodormancy is the most familiar type. The growth halt originates from within the dormant structure itself, triggered by environmental cues like shortening day length or prolonged cold. A deciduous tree entering winter dormancy is the classic example. Even if you brought a branch indoors to warm temperatures in mid-January, it wouldn’t leaf out immediately because the internal dormancy program hasn’t yet been satisfied. The bud itself “knows” it needs more cold exposure before it’s safe to grow.
Paradormancy occurs when a signal from another part of the plant suppresses growth in a different structure. The most common example is apical dominance, where the growing tip of a stem produces hormones that prevent lateral buds below it from sprouting. Those buds are perfectly capable of growing, but they’re being chemically held in check. If you prune the tip, the lateral buds often break free and start growing within days.
Ecodormancy is the simplest type. Growth pauses because one or more environmental factors, like temperature, water, or nutrients, are inadequate. Once conditions improve, growth resumes without any special internal requirements. Think of a lawn that goes brown during a summer drought and greens up again after rain. The grass wasn’t running an internal dormancy program; it just lacked water.
How Hormones Control the On/Off Switch
Two plant hormones act as opposing forces in dormancy regulation. One promotes dormancy, while the other promotes growth. The ratio between them largely determines whether a plant stays dormant or wakes up.
Abscisic acid (ABA) is the dormancy promoter. As fall approaches, ABA levels rise in buds and seeds, slowing cell division and triggering protective responses. Research in barley seeds found a very strong negative correlation (r = 0.85) between ABA levels in the embryo and germination rates. In plain terms, the more ABA present, the less likely the seed is to sprout.
Gibberellins work in the opposite direction. These growth-promoting hormones rise as dormancy breaks, stimulating cell elongation and seed germination. The same barley research showed a strong positive correlation (r = 0.64) between gibberellin levels and germination. What matters most isn’t the absolute amount of either hormone but the ratio between them. When ABA dominates, the plant stays dormant. When gibberellins gain the upper hand, growth resumes. That ratio shift showed a correlation of 0.84 with germination variation, making it one of the strongest predictors of when dormancy ends.
What Triggers Dormancy in the First Place
Plants don’t wait for freezing temperatures to prepare for winter. They start months earlier by reading day length. Specialized light-sensing proteins called phytochromes detect the ratio of red to far-red light in the environment. As days shorten in late summer and early fall, the balance of these proteins shifts, signaling the plant to begin preparing for dormancy. This is why trees in northern climates start changing color and dropping leaves well before the first frost. They’re responding to photoperiod, not temperature.
Temperature plays a supporting role. Cool nights reinforce the photoperiod signal, accelerating ABA production and nutrient translocation from leaves back into woody tissues. By the time hard frost arrives, a well-prepared tree has already sealed off its leaf connections, stored energy as starch in its roots and trunk, and fortified its bud cells against freezing.
For seeds, the triggers vary. Some seeds enter dormancy as part of their development on the parent plant, arriving in the soil already dormant. Others respond to the conditions they land in. A seed that falls in autumn may require a full winter of cold before it will germinate, ensuring it doesn’t sprout just before a killing freeze.
How Plants Protect Themselves During Dormancy
Dormancy isn’t just about stopping growth. It also involves active cellular defense, particularly against cold and dehydration. One of the key protective tools is a family of proteins called dehydrins. These are intrinsically disordered proteins, meaning they lack a fixed shape, which allows them to interact flexibly with cell structures under stress.
Dehydrins bind directly to cell membranes, stabilizing them during freezing and dehydration. When ice forms outside a cell, it draws water out through osmosis, threatening to collapse the membrane. Dehydrins attach to the fatty molecules that make up the membrane, limiting their movement and preventing the kind of structural damage that would kill the cell. Specific dehydrin segments have been shown to reduce the temperature at which membranes undergo damaging phase transitions, effectively lowering the cell’s freezing point. These proteins also protect enzymes and even stabilize DNA structure during stress.
This protective chemistry explains why a dormant plant can survive temperatures that would destroy the same tissue during active growth. A peach bud in full dormancy can tolerate far colder conditions than the same bud after it begins swelling in spring.
Seed Dormancy: Physical vs. Physiological
Seeds use two broad strategies to stay dormant. Physical dormancy involves a seed coat that is literally waterproof. Until water can penetrate the coat, germination is impossible regardless of temperature or light conditions. This type is common in legume families and geranium relatives. In nature, the coat breaks down through soil microbes, fire, or repeated freeze-thaw cycles. In some species, hot water followed by rapid cooling cracks the coat at a specific weak point near the seed’s hilum (the scar where it was attached to the parent plant).
Physiological dormancy is more complex. The embryo inside the seed is chemically inhibited from growing, typically through high ABA levels. Breaking this type of dormancy usually requires a period of cold, moist conditions that gradually shifts the hormone balance toward gibberellins. Some seeds combine both strategies: they have an underdeveloped embryo that needs time to grow inside the seed coat before it can even respond to germination cues. This is called morphophysiological dormancy, and it can delay germination for a year or more.
Chilling Requirements for Fruit Trees
Temperate fruit trees need a specific amount of winter cold to properly break endodormancy and bloom normally in spring. This is measured in “chill hours,” typically defined as each hour spent between 32°F and 45°F. The most efficient temperatures for satisfying chilling requirements fall in that range, though temperatures up to 50°F contribute to some degree.
Different species and varieties have dramatically different needs. Apple varieties range from 200 to 1,000 chill hours, while peach varieties need 200 to 800 hours. This range matters enormously for growers choosing varieties suited to their climate. A high-chill apple variety planted in a mild-winter area may never bloom properly, producing sparse, uneven flowering and poor fruit set. Conversely, a low-chill variety in a cold climate will satisfy its requirement early and risk blooming during a late freeze.
Breaking Dormancy in Your Garden
If you’re starting plants from seed, you may need to break dormancy artificially. The technique depends on the type of dormancy involved.
For physiological dormancy, cold stratification mimics winter. Place seeds in a moist medium like damp sand or peat moss, seal them in a bag, and refrigerate for the required period, which ranges from a few weeks to several months depending on the species. The cold, moist environment gradually lowers ABA and raises gibberellin levels, just as a natural winter would.
For physical dormancy, you need to breach the seed coat. Mechanical scarification, using sandpaper or a razor blade to nick the coat away from the hilum, is the most controlled method. Heat treatments also work: exposing seeds to water at 80°C (176°F) for 10 minutes can crack the coat at its weakest point. Alternating cycles of hot water and ice water are particularly effective for hard-coated legume seeds, sometimes requiring 10 or more cycles to achieve reliable water uptake.
How Climate Change Affects Dormancy
Rising winter temperatures are disrupting dormancy cycles in measurable ways. Field studies show that reduced cold accumulation during warmer winters has, in some cases, actually extended dormancy duration rather than shortening it. This seems counterintuitive, but it makes biological sense: trees that don’t receive enough chilling become less responsive to warm spring temperatures, requiring more heat to trigger leaf-out. The result is that the well-documented trend toward earlier spring leaf emergence may be slowing in some regions.
However, modeling from a December 2024 study suggests that decreasing chilling from climate warming may not significantly constrain shifts toward earlier leaf emergence worldwide in the near future. The picture is complex and varies by species and region. What’s clear is that the carefully calibrated relationship between winter cold and spring growth, one that plants evolved over millions of years, is being tested by a pace of temperature change that exceeds anything in the recent geological record. For fruit growers, this means variety selection based on historical chill hours is becoming less reliable, and low-chill varieties are gaining importance in regions that once had dependably cold winters.