Tomato plants are sensitive to cold temperatures and have specific tolerances:

• Tomato plants generally suffer cold damage if overnight temperatures fall below 12°C (55°F). Night temperatures below this can stunt growth and reduce flowering and fruit set

• Tomato seedlings are particularly vulnerable to cold and can be damaged below 15.5°C (60°F). Seeds will not germinate below about 10°C (50°F)

• Mature tomato plants can tolerate temperatures down to about 10°C (50°F) but fruit set and flowering are negatively affected below this threshold

• Exposure to chilling temperatures between 0°C to 5°C (32°F to 41°F) causes chilling injury, including stunted growth, wilting, and leaf damage. Frost or freezing temperatures (0°C or below) cause more severe damage and can kill tomato plants

• Some cold-hardy tomato varieties can tolerate cooler conditions better, with certain cultivars able to set fruit at or just below 13°C (55°F)

In summary, tomato plants thrive best when night temperatures stay above 12-15°C (55-60°F). Temperatures below 10°C (50°F) risk cold injury and poor fruit development, while frost and freezing temperatures will severely damage or kill the plants. Protecting tomatoes from cold snaps and frost is critical for healthy growth and fruit production. This means in practical terms:

• Avoid planting tomatoes outdoors until nighttime temperatures consistently stay above 12°C (55°F).
• Use covers or move plants indoors if temperatures are forecast to drop below this.
• Be aware that prolonged exposure to temperatures near freezing (0-5°C) causes chilling injuries and frost kills tomatoes