It is a common misconception that tree planting must be reserved for the mild weather of spring or fall. Planting trees in winter is entirely possible and often advantageous, provided the ground remains workable. The season from late fall, after leaves have dropped, until early spring offers a significant window for successful tree establishment. This practice hinges on understanding the tree’s internal state and requires modifications to planting techniques and post-planting care.
The Advantage of Dormancy
The primary biological reason winter planting is successful is the tree’s state of dormancy, a survival mechanism triggered by shortening daylight hours and cooling temperatures. Dormancy is a phase where the tree remains alive but has significantly slowed its metabolic processes, effectively entering a resting state. This physiological shutdown drastically reduces the tree’s demand for water and nutrients, which is advantageous during transplanting.
For deciduous trees, the absence of foliage eliminates water loss through transpiration, a major source of stress in warmer months. With above-ground functions minimized, the tree’s stored energy reserves are redirected to the root system. Root growth often continues slowly in soil just above freezing, allowing new feeder roots to establish contact with the surrounding earth.
Planting during this dormant phase minimizes transplant shock. When a tree is planted while actively growing, it must support foliage while recovering from root disturbance. By planting in winter, the tree dedicates its initial energy entirely to root establishment without the burden of leaf production. This head start allows the tree to wake up in spring with a more established foundation, prepared for rapid new growth.
Defining Workable Conditions
While dormancy makes a tree ready for planting, environmental conditions must be suitable for the physical process of digging and settling the root ball. A “workable winter” is defined by soil that is unfrozen, non-saturated, and easily manipulated. The temperature of the soil, not the air, is the most important factor, as planting must cease when the soil is frozen solid.
The threshold for stopping work is when the ground is frozen deeper than an inch or two, or when air temperatures consistently fail to rise above freezing. Digging into frozen soil causes trauma to the root system and creates frozen clods that prevent proper soil-to-root contact. Planting in overly wet or muddy soil due to winter thaws is equally detrimental.
Saturated soil is prone to compaction and poor aeration, which can suffocate new roots. When backfilling with wet soil, it is difficult to eliminate air pockets. These pockets can lead to root desiccation or fill with water that subsequently freezes, causing damage. Operations must be limited to periods when the soil is dry enough to crumble easily and is completely frost-free.
Adjusting Planting Techniques for Cold Soil
The physical process of planting in cold, workable soil requires specific modifications to ensure success. The planting hole should be dug wide—ideally two to three times the diameter of the root ball—but only as deep as the root ball itself. The trunk flare, where the roots spread from the trunk, must sit slightly above the surrounding ground level to prevent the tree from being planted too deeply.
When handling a balled and burlapped tree, the root ball must be handled with care, as cold roots are brittle and prone to breakage. Remove or cut away the burlap and any wire basket material only after the tree is correctly positioned. The excavated soil used for backfilling should not be heavily amended with organic matter, as this discourages roots from growing into the native soil.
To achieve firm soil-to-root contact and eliminate air pockets, backfill the hole incrementally. Add the soil in small layers and settle each layer thoroughly with water, which is more effective than tamping with a shovel. Using tepid water can help moderate the immediate temperature shock to the roots. A final, deep watering is required immediately after planting to ensure the root ball is fully hydrated before the ground potentially freezes.
Essential Post-Planting Winter Protection
Once the tree is in the ground, measures must be taken to protect it through the remainder of the cold season. Applying a thick layer of organic mulch is one of the most effective steps, acting as a natural insulator for the root zone. A 3- to 4-inch layer of wood chips or shredded bark helps moderate soil temperature fluctuations, minimizing damaging freeze-thaw cycles that can heave a young tree out of the ground.
The mulch layer should be spread in a wide, shallow ring, forming a “mulch donut” that extends several feet from the trunk. Keep the material several inches away from the trunk itself, as placing mulch directly against the bark encourages rot and creates a haven for rodents. Protecting the trunk from sun scald is also necessary, especially for thin-barked species.
Sun scald occurs when the winter sun warms the bark, stimulating cellular activity that is rapidly destroyed when temperatures plummet after sunset. Protect the trunk by wrapping it with a light-colored paper wrap or plastic guard. The tree’s water needs do not entirely cease during winter, particularly for evergreens. Intermittent watering during dry periods or mild thaws is necessary to prevent root desiccation until spring.