Bare root strawberries are dormant plants shipped without soil, consisting primarily of the crown and roots. This state of suspended growth provides a natural defense against cold temperatures. While resilient, their survival against frost depends on their current stage of development and the severity of the cold event. A dormant plant can withstand conditions that would kill an actively growing one, making timing and protection measures important for a successful yield.
Dormancy and the Frost Resilience of Bare Roots
The survival mechanism of a bare root strawberry plant is rooted in its dormancy, a period where metabolic activity is significantly slowed. When fully acclimated to cold weather, the central growing point, known as the crown, can tolerate temperatures as low as 10°F (-12°C). This resilience is due to internal physiological changes that prevent ice crystal formation within the cells.
The roots are hardy in cold soil, but the crown is the most sensitive structure, as it contains the buds for future leaves and flowers. Once the plant breaks dormancy and begins to sprout new roots or tender green leaves, cold tolerance decreases rapidly. At this active growth stage, new foliage is susceptible to damage around 22°F (-5.5°C), and developing flower buds become even more vulnerable.
Optimal Planting Timing to Avoid Risk
The primary strategy for mitigating frost risk is to plant the bare roots while they are still dormant. Planting should occur as soon as the soil is workable—no longer frozen and dry enough to prevent compaction. This timing often falls several weeks before the last expected spring frost.
It is recommended to plant when the soil temperature consistently registers above 40°F (4°C), allowing for initial root establishment before the crown fully wakes up. Planting dormant material early encourages robust root growth before the plant dedicates energy to producing leaves and flowers. If the bare roots arrive before the ground is ready, they can be stored temporarily in a refrigerator for up to two weeks.
To store them, keep the plants in their original packaging or a sealed plastic bag with damp material to prevent drying out. If planting must be delayed longer, a method called “heeling in” can be used, where the plants are temporarily buried in a trench of soil or sand outdoors. This temporary planting keeps the crowns cool and moist until the permanent site is prepared.
Immediate Protection Measures Against Unexpected Cold
Once bare root plants are in the ground and a sudden late frost is forecast, immediate protection is necessary, particularly if new growth has started. Floating row covers, made from lightweight fabric like agribon, are highly effective and can elevate the temperature beneath them by 4 to 6 degrees Fahrenheit. These covers should be placed over the plants in the late afternoon before the temperature drops, ensuring they cover the crown completely.
A simpler measure involves applying a thick layer of loose straw mulch directly over the planted crowns to insulate them. This straw must be removed promptly the following morning to prevent smothering the new growth.
Watering the garden bed thoroughly just before the freezing event is another technique, as moist soil holds significantly more heat than dry soil. The water releases this stored heat slowly throughout the night, slightly raising the ambient air temperature surrounding the plants. For more severe freezes, some growers utilize overhead sprinkler irrigation, which protects the plant by continuously coating it in water. The process of water freezing into ice releases latent heat, maintaining the plant tissue temperature near 32°F (0°C), but this method requires careful monitoring.
Assessing and Treating Frost Damage
After a frost event, wait a few days before assessing the full extent of the damage. Immediate signs of injury are often seen in the leaves, which may appear water-soaked, black, or have curled edges. Minor damage to the foliage is rarely fatal, but recovery depends on the health of the crown.
To check for damage within the crown, cut a cross-section of the central tissue. Healthy crown tissue appears creamy white or pale yellow-green. Frost-damaged tissue shows a brown or dark, mushy discoloration, indicating that the internal cells have been killed.
If only the leaves are damaged, the plant will likely recover by sending up new growth from the uninjured crown. Trim off the severely blackened leaves to allow the plant to focus its energy on new development.
If the crown exhibits extensive dark brown discoloration, the plant may not survive. However, patience is advised, as small, healthy portions of the crown can sometimes produce new shoots.