Tomato plants are sensitive to temperature fluctuations, which influence their growth, overall health, and fruit production. Understanding their specific temperature requirements and tolerances is important for a successful harvest. Temperature impacts every stage, from seed germination to fruit ripening, making it a central factor in cultivation.
Ideal Temperature Range for Tomatoes
Tomato plants thrive within a specific temperature range. For optimal growth, flowering, and fruit setting, daytime temperatures of 70°F to 82°F (21°C to 27°C) are ideal. Nighttime temperatures of 62°F to 64°F (17°C to 18°C) are optimal for fruit production. Consistent temperatures promote efficient photosynthesis.
During flowering, optimal temperatures are important for pollen viability and fertilization. If temperatures deviate, pollen development and fertilization can be compromised. For seed germination, soil temperatures between 65°F and 85°F (18°C and 29°C) are ideal. These conditions allow efficient nutrient absorption and robust root development.
How Cold Temperatures Affect Tomato Plants
Temperatures below the ideal range negatively impact tomato plants. Between 32°F (0°C) and 50°F (10°C), plants may survive but won’t grow or produce ripe fruit. Extended periods below 60°F (16°C) can cause nutrient deficiency, affecting phosphorus uptake, and stunt growth.
Chilling injury occurs between 32°F (0°C) and 41°F (5°C), causing stunted growth, wilting, and leaf discoloration. Nighttime temperatures below 55°F (13°C) can hinder pollen development, leading to blossom drop and reduced fruit set. Frost, which can occur even around 40°F (4°C) with moisture, is damaging as it forms ice crystals within plant cells, causing severe tissue damage or plant death, especially below 28°F (-2.2°C).
How Hot Temperatures Affect Tomato Plants
Temperatures exceeding the optimal range challenge tomato plants, affecting fruit production. When daytime temperatures consistently exceed 85°F (29°C) and nighttime temperatures remain above 75°F (24°C), flowers may fail to pollinate, causing blossom drop. High heat can reduce pollen viability or cause it to burst. Sustained heat above 90°F (32°C) can reduce fruit set and yield.
High temperatures also impact fruit development and quality. Above 86°F (30°C), lycopene, the red pigment, may not form properly, leading to uneven ripening or lack of full color. Prolonged heat can accelerate ripening but reduce fruit size and quality. Sunscald can occur on developing fruit exposed to intense sun and heat, appearing as light-colored, leathery spots.
Protecting Tomato Plants from Temperature Extremes
Protecting tomato plants from temperature extremes involves strategies to mitigate stress. To shield plants from cold snaps or early frosts, use row covers or cloches, creating a warmer microclimate. Watering soil deeply before a predicted freeze helps, as moist soil retains more heat than dry soil, radiating warmth overnight. Move potted plants indoors for immediate protection from cold.
In hot conditions, providing shade is an effective method to reduce heat stress. Shade cloth (around 50% blockage) can lower ambient temperatures by up to 10 degrees and protect plants during the hottest parts of the day. Adequate and consistent watering is important, as plants transpire more rapidly in heat. Applying a 2-3 inch layer of organic mulch helps retain soil moisture and regulate soil temperature, keeping roots cooler. Choosing heat-tolerant or cold-tolerant varieties provides built-in resilience.
Timing Your Tomato Planting for Optimal Temperatures
Strategic planting based on temperature is important for a successful tomato harvest. Wait until all danger of the last frost has passed before transplanting tomatoes outdoors. Soil temperature is a particularly important factor, as cold soil can stunt root development and nutrient absorption.
Ideally, soil temperatures should consistently reach at least 60°F (16°C), with 65°F to 70°F (18°C to 21°C) optimal for transplanting. Nighttime air temperatures should also consistently remain above 50°F (10°C) to ensure proper fruit set. Monitoring local frost dates and using a soil thermometer helps determine planting time. For an extended harvest, succession planting (introducing new plants at intervals) can be considered in regions with longer growing seasons.