The strawberry, a member of the genus Fragaria, is a temperate perennial plant whose life cycle, productivity, and fruit quality are profoundly influenced by temperature. Unlike tropical fruits, the strawberry plant requires a specific sequence of warm and cold periods to trigger vegetative growth, flower bud formation, and successful fruiting. Managing the plant’s thermal environment is fundamental to successful cultivation. Both excessively cold and excessively high temperatures can drastically reduce the final yield and the market value of the fruit, dictating the strategies growers must employ.
The Ideal Temperature Zone
The temperature range that maximizes a strawberry plant’s productivity is relatively narrow, shifting depending on the growth stage. For robust vegetative growth and maximizing photosynthesis, the plant performs best when daytime temperatures are sustained between 64°F and 79°F (18°C and 26°C). Photosynthesis, the process that fuels the plant, reaches its optimal rate around 68°F (20°C).
During the reproductive phase, the ideal temperature profile involves a significant difference between day and night. Growers often aim for daytime highs of 68°F to 75°F (20°C to 24°C), paired with cooler nighttime temperatures around 50°F to 54°F (10°C to 12°C). These cooler nights are important for fruit quality, as lower temperatures during maturation enhance the accumulation of sugars, resulting in a sweeter, more flavorful berry. Conversely, high night temperatures, particularly exceeding 65°F (18°C), can increase fruit acidity, negatively impacting the sugar-to-acid ratio.
Surviving the Deep Cold
Strawberry plants, especially those grown in temperate regions, have a built-in mechanism to survive winter through a state of dormancy. This period requires a specific amount of chilling to prepare the plant for the next season’s growth. In this dormant state, the plant’s crown—the short stem where the leaves and roots originate—can tolerate temperatures as low as 10°F to 15°F (-12°C to -9°C).
Before winter, plants engage in a process called cold hardening, where exposure to non-freezing cold temperatures induces physiological changes to mitigate cellular injury. This acclimation allows the plant tissues to survive freezing conditions by altering internal chemistry. The greatest temperature-related risk occurs in spring once the plant breaks dormancy and begins flowering.
The plant’s reproductive structures are highly vulnerable to frost events. The specific temperature threshold for damage depends on the flower’s developmental stage, with open blossoms being the most sensitive. An open flower is typically killed when tissue temperature drops below 30°F (-1°C). A developing green fruit is slightly more tolerant, suffering damage below 28°F (-2°C). Even a tight, unopened flower bud, often called a ‘popcorn’ stage bud, is at risk once temperatures drop below 26.5°F (-3°C).
When High Temperatures Cause Stress
Temperatures consistently above 85°F to 86°F (30°C) initiate a cascade of detrimental effects known as heat stress in the strawberry plant. One primary consequence is a significant reduction in the rate of photosynthesis, which limits the energy available for growth and fruit production. Prolonged exposure to heat can also induce a temporary state of reproductive shutdown in some cultivars, often referred to as thermo-dormancy, where flower bud formation is inhibited.
The quality of the fruit suffers markedly under high thermal load. Berries grown under high day and night temperatures, such as 86°F/68°F (30°C/20°C), have been shown to be smaller and irregular in shape, with a lower intensity of red color. High heat can cause the fruit tissue to become soft and prone to internal breakdown, reducing its shelf life and commercial appeal. In extreme heat, the viability of pollen is reduced, leading to poor fruit set and the development of small or misshapen berries.
Protecting Strawberries from Temperature Swings
Mitigating cold damage during the spring flowering period often relies on the strategic use of water and physical barriers. Overhead irrigation is a common method for frost protection, working by continuously coating the plants with water. As the water freezes, it releases latent heat, which keeps the plant tissue insulated just above the lethal freezing point. This method is generally effective until air temperatures drop below 20°F (-7°C).
Floating row covers, which are sheets of lightweight fabric, provide another layer of defense by trapping heat radiating from the soil and reducing evaporative cooling. Depending on their weight, these covers can raise the canopy temperature by two to ten degrees Fahrenheit. For winter dormancy protection, a thick layer of straw mulch is often applied over the crowns to provide insulation against sustained deep freezes.
To combat the negative effects of summer heat, passive and active cooling measures can be used.
Cooling Measures
Applying a shade cloth, typically rated for 50% to 65% light reduction, can decrease the temperature around the canopy and prevent sunscald and fruit softening. Maintaining soil moisture through strategic watering is also important, as water stress is exacerbated by high temperatures. Reflective mulches can also be used on planting beds to help keep the soil temperature cooler, which protects the shallow root system from excessive heat absorption.