Trees in temperate climates exhibit a dramatic change in appearance as winter approaches, leading to the assumption that all biological processes cease entirely. While the visible parts of the tree appear static after shedding their leaves, the underground system operates on a different timetable. Roots do not always follow the same strict growth cycle as the above-ground canopy. The conditional activities beneath the soil surface determine a tree’s health and ability to thrive once spring returns.
The Conditions for Winter Root Activity
The answer to whether tree roots grow in the winter is yes, but this activity is highly dependent on environmental factors. Above-ground growth, the shoot system, enters deep dormancy triggered by the shortening of daylight hours in the fall. In contrast, the root system’s activity is governed more by the physical conditions of the soil than by day length.
Root growth does not halt simply because the air temperature drops or the above-ground portion is dormant. Roots maintain a state of readiness, sometimes called quiescence, allowing them to take advantage of favorable soil conditions throughout the winter. This is particularly true for deeper roots, which benefit from the insulating properties of the earth. Soil at lower depths remains warmer and more stable than the surface layer, shielding them from rapid temperature fluctuations.
As long as the soil remains unfrozen and contains adequate moisture, the roots of many tree species can continue a slow rate of growth. This conditional growth provides a strategic advantage, enabling the tree to expand its resource-gathering network before the demands of spring leaf-out begin. Fine, feeder roots near the surface are more susceptible to freezing and generally cease activity sooner than their deeper counterparts.
How Soil Temperature Governs Growth
The rate of root growth is controlled by the specific thermal environment of the soil, not air temperature. Most tree species require the soil to be above a certain temperature threshold to sustain cell division and elongation. For many species, this minimum soil temperature for root growth is in the range of 32°F to 41°F (0°C to 5°C).
This threshold is sometimes referred to as the “biological zero” for plant activity, marking the point below which metabolic processes are drastically reduced. When the soil temperature drops below approximately 40°F (4.4°C), root elongation slows significantly, and below 32°F (0°C), growth essentially stops. Minimum temperatures for root growth vary between 2.3°C and 4.2°C across different broad-leaved tree species.
If the soil freezes solid, all metabolic growth ceases because the root cells cannot function without liquid water and are susceptible to damage from ice formation. However, in regions where the soil remains unfrozen or is insulated by a persistent layer of snow, roots can maintain a slow but steady pace. This ability to grow at low temperatures allows trees to repair damaged root tips and prepare for the intense resource needs of the upcoming growing season.
Essential Root Functions During Dormancy
Even when temperatures fall below the threshold for active growth, roots perform functions necessary for the tree’s survival and spring reawakening. The root system serves as a storage depot for energy reserves produced during the previous summer. These reserves are primarily starches and carbohydrates, which are converted to sugars to fuel the rapid growth of buds in spring.
Roots also continue the process of water and nutrient absorption, provided the soil is not completely frozen. This function is important for evergreen trees, which lose water through their leaves in winter and must replace it to prevent desiccation. Nutrient uptake is facilitated by minimal cellular respiration occurring in the roots, maintaining the tree’s overall health.
The root system dedicates energy to maintenance and repair of existing structures during the colder months. This involves processes like replacing fine feeder roots damaged by soil freezing or pests. By keeping these non-growth activities running, the root system ensures that the tree is physically and energetically ready for bud break, which requires a surge of resources before the soil fully warms up.