02/04/2026
Good information on how plants are acting with the weather we've had this winter.
Dormancy and why plants were behaving strangely
by Abiya Saeed, MSU Extension Horticulture Specialist, [email protected]
We have heard countless reports of strange plant occurrences this fall/winter, from garlic sprouting in vegetable gardens, pansies flowering in landscape beds, dandelions blooming and forming seedheads, to honeysuckles and other woody plants starting to leaf out and bloom in December. With the uncharacteristically warm temperatures that we have experienced throughout Montana this past month, many of these seemingly strange plant behaviors do have a possible explanation.
What is dormancy?
Many plants undergo a process called "dormancy", where they are not actively growing, though still alive. Dormancy is a survival tactic for certain plants, where they slow or stop active growth to conserve energy and protect themselves. This process can look different depending on the type of plant, and is usually most noticeable in deciduous trees and shrubs (the woody plants that drop their leaves in the fall/winter). Though we may think of dormancy as a response to cold/dry conditions, there are two different types of dormancy that plants undergo: endodormancy and ecodormancy (and these are triggered by different things, serving slightly different functions).
Endodormancy is caused by the plant's internal clock (and is a result of physiological processes that prevent active growth in plants until a specific duration or chilling period has occurred). This process is critical for plants to store energy that will support spring growth, in addition to protecting these plants in adverse conditions. This is also the process that prevents certain plants from resuming active growth in the winter months, regardless of temperature fluctuations, even if environmental conditions could be ideal for growth and development (like some of the conditions that we have seen in many parts of the state over the past few weeks). The temperature threshold for these chilling hours is usually between 32 - 45 F, and the duration of the chilling period required to break endodormancy varies depending on the type of plant: from a couple of hundred hours (which could be less than two weeks) to over 1000 hours. Plants that cannot meet the required chilling hours may have poor growth the following spring (which is why we can't successfully grow certain plant varieties with longer chilling requirements in warmer geographic regions). Alternatively, plants that have a very short endodormancy period may be more susceptible to winter-related injuries and damage when environmental conditions fluctuate (for example, a really warm early spring period, followed by an often inevitable cold snap).
The second type of dormancy is called ecodormancy, and this is in response to environmental conditions (such as temperature and moisture availability). Once the chilling period of endodormancy has been completed, ecodormancy is the reason that plants may still be dormant late in spring or may start to undergo dormancy [including premature leaf drop] earlier in the fall (in response to stressors such as lack of moisture availability and drought stress).
Why we may be seeing unusual plant growth in the winter:
What we may be seeing in terms of unusual plant growth (especially in perennial plants) over the past few weeks could be the result of a combination of these two processes. With enough time spanning the chilling temperatures required for endodormancy (32 - 45 F) in certain plant cultivars, followed by unseasonably warm December temperatures that can trick plants into thinking that spring has arrived, we may be seeing new plant growth that usually doesn't occur until spring (when we typically have warming post-winter temperatures). With December temps warm enough (with some locations showing extended periods of temperatures ranging from 50 - 65F) ecodormancy may not prevent the plants from resuming growth and development, especially in plant cultivars that may have shorter endodormancy periods.
What can we expect in the spring?
Although regionally adapted and hardy perennial plants can handle Montana's cold winters when they are dormant, new growth such as leaf, bud, and especially flower tissues are not as hardy (and are susceptible to winter-related injuries such as frost and cold-temperature damage and dieback). As a result, we may see some winter-related damage including dieback and poor spring regrowth in plants that resumed growth and development in the winter months.
That being said, most adapted perennials will likely recover from this damage over time (though they may require a little extra pruning to remove any dead/damaged sections). Though it is possible to see some branch and tip dieback and less flowering and/or fruit production as a result of potential winter damage; overall hardy and healthy trees, shrubs, and the root systems of herbaceous perennials are unlikely to be seriously damaged. Monitor these plants over the course of the growing season, and make sure they remain otherwise healthy.
Fall planted bulbs (like garlic) that may have started leafing out this past month can be covered in a 3-4 inch layer of mulch (such as leaflitter or w**d and herbicide-free straw). There is often enough energy stored in the bulb, that some early growth and potential damage may not have too much of an impact on your garlic harvest next summer.
Understanding how dormancy processes work and what causes them can help us make better decisions when choosing tree and shrub varieties to grow in our region and selecting plants that will be less likely to exhibit cold-weather related injuries and dieback when inevitable temperature fluctuations occur.
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