The survival of the cultivated strawberry, Fragaria x ananassa, is fundamentally dictated by its ability to withstand temperature extremes. The plant’s tolerance to heat or cold depends highly on its specific growth stage and the duration of the thermal exposure. Temperature is the primary limiting factor for both growth rate and survival, influencing everything from vegetative development to fruit production. Understanding these thermal thresholds is necessary for successful cultivation.
Lethal Low Temperatures and Cold Damage
The temperature that kills a strawberry plant differs significantly depending on whether the plant is dormant or actively growing. A dormant plant exhibits remarkable cold tolerance, concentrated in the crown (the short stem where buds and roots originate). A well-acclimated, dormant crown can survive temperatures as low as 10°F (-12°C), and sometimes down to 0°F (-18°C), especially when insulated. Plant death occurs when tissue water inside the crown freezes, causing cellular rupture.
When unprotected, severe crown damage occurs around 15.8°F (-9°C), with lethal temperatures typically ranging between 9.5°F and 10.4°F (-12.5°C and -12°C). The greatest cold threat comes in the spring when the plant is actively growing. Temperatures that kill the potential harvest are much higher than those that kill the plant, and brief exposure during bloom can lead to substantial yield loss.
The flowers and young fruit are the most sensitive parts to spring frosts. Open blossoms are damaged when the temperature drops to 30°F (-1.1°C), resulting in a blackened center indicating the death of the pistil. Tightly closed flower buds can survive down to about 22°F (-5.5°C). Small green fruit sustains damage only when temperatures fall to 28°F (-2.2°C).
High Temperature Stress and Heat Death
Strawberry plants are cool-weather crops, and sustained high temperatures cause significant stress. The ideal temperature range for robust growth is between 60°F and 85°F (15°C and 29°C). When temperatures consistently rise above 85°F (29°C), growth slows dramatically. This stress can lead to dormancy, where the plant continues vegetative growth but stops initiating new flowers, halting fruit production.
Sustained temperatures above 90°F (32°C) cause the plant’s respiration rate to exceed its photosynthesis rate, leading to a net energy deficit. Prolonged periods above 100°F (38°C), especially combined with low humidity or insufficient water, cause irreversible damage. Leaves can scorch, and roots suffer damage from elevated soil temperature, leading to plant collapse and death. High heat also impairs pollen viability, preventing successful fruit set.
Protecting Strawberry Plants From Freezing
Protecting strawberry plants from freezing involves steps tailored to the plant’s growth stage. During winter, the primary goal is to insulate the dormant crowns. A heavy layer of mulch, such as straw or pine needles, should be applied in late autumn after the first light frosts. This mulch acts as an insulator, preventing the crown tissue from reaching lethal temperatures.
In spring, temporary measures protect vulnerable blossoms from unexpected frosts. Floating fabric row covers are effective, raising the temperature underneath by a few degrees to protect against light frost. For more severe cold, growers employ overhead irrigation, which relies on the physics of fusion. As water turns into ice on the plant surface, it releases latent heat, maintaining tissue temperature near 32°F (0°C).
This method requires continuous water application until the ice melts naturally the following morning, and must start before the air temperature drops too far. Stopping irrigation prematurely can cause the ice layer to drop rapidly in temperature, resulting in severe damage. Combining row covers and overhead irrigation provides the highest protection, shielding plants even below 20°F (-6.7°C).
Strategies for Managing Extreme Summer Heat
Mitigating the effects of extreme summer heat maintains plant health and fruit production. Strategic use of shade cloth during the hottest parts of the day is effective. A cloth blocking 30% to 40% of sunlight can lower the air temperature by 10°F to 15°F, preserving pollen viability and preventing leaf scorching. Shading is most beneficial during peak afternoon heat, typically between 11 a.m. and 4 p.m.
Water management focuses on keeping the root zone consistently cool and hydrated. It is best to water deeply and early in the morning to minimize evaporation and allow absorption before midday heat. Organic mulch, such as straw or shredded leaves, insulates the soil, keeps roots from overheating, and retains moisture. Cooling the root zone helps the plant cope with high air temperatures.