Tomatoes grow best between 60°F and 85°F (16–29°C). Below 50°F growth stalls, below 33°F frost kills unprotected plants, and above 90°F flowers drop. Enter a temperature below to see instantly whether it is safe to plant, grow, or protect your tomatoes, in Fahrenheit or Celsius.
Try a preset:
Your entry stays in your browser. Nothing is sent to a server or saved to an account.
What your result means: the colored verdict interprets the temperature for tomatoes, from frost risk through the ideal band to heat stress, and tells you the action to take. Use the daytime high to judge heat and the overnight low to judge cold.
How do you use the temperature checker?
Enter a temperature, choose the unit, and press check. The tool converts to Fahrenheit if needed and reads the value against tomato tolerance bands.
- Enter the temperature you want to check, current or forecast.
- Choose Fahrenheit or Celsius. The tool converts Celsius internally.
- Press check to see a color-coded verdict and the recommended action.
What each verdict means
| Band | Meaning | Action |
|---|---|---|
| Frost / too cold | At or below 50°F growth stalls; below 33°F is lethal | Do not plant; cover or move plants indoors |
| Marginal | 50–60°F, air warming but soil often still cold | Harden off; wait to transplant |
| Ideal | 60–85°F, the sweet spot | Plant and grow normally |
| Heat stress / too hot | Above 85°F fruit set drops; above 95°F flowers fall | Shade, mulch, deep water |
What temperature is safe for tomatoes?
Tomatoes are a warm-season crop that grows best between 60°F and 85°F (16–29°C). They tolerate brief dips but suffer lasting damage from frost and prolonged heat. The checker uses these research-based bands, which the table below the tool lists in full, to translate any reading into a plant-safe verdict.
How does the temperature check work?
The tool first converts Celsius to Fahrenheit, then places the value into one of six bands and returns the matching verdict and advice.
Below 33F frost · 33 to 50F too cold · 50 to 60F marginal
60 to 85F ideal · 85 to 95F heat stress · above 95F too hot
The bands reflect how tomato roots, flowers, and fruit respond: cold soil stalls roots, and high heat prevents pollination, causing blossom drop.
Worked example
Say a spring afternoon reads 16°C. The tool multiplies 16 by 9, divides by 5, and adds 32 to get about 61°F. That lands just inside the ideal band, so the verdict is that conditions are suitable for planting and growing, provided the overnight low also stays above 50°F.
Factors that change what is safe
- Day versus night: a warm day with a cold night below 50°F still stresses plants; check both.
- Soil temperature: soil lags behind air, so a mild air reading can hide cold roots. Aim for soil near 60°F to transplant.
- Plant stage: young seedlings tolerate less cold and heat than established plants.
- Humidity and wind: dry heat and hot wind worsen blossom drop above 90°F.
- Duration: a brief spike matters less than several days in a stress band.
Understanding the bands
| Temperature | What it means | What to do |
|---|---|---|
| Below 33°F (0°C) | Frost, kills unprotected plants | Cover or bring containers indoors |
| 33–50°F (0–10°C) | Too cold, growth stalls | Do not plant; protect existing plants |
| 50–60°F (10–16°C) | Marginal, soil often too cold | Wait to transplant; harden off |
| 60–85°F (16–29°C) | Ideal growing range | Plant and grow normally |
| 85–95°F (29–35°C) | Heat stress, poor fruit set | Shade, water deeply, mulch |
| Above 95°F (35°C) | Blossom drop and sunscald risk | Afternoon shade and water |
When to use it
Check temperatures in spring before transplanting to confirm both day and night readings are safe, during summer heat waves to decide whether to add shade cloth, and in fall as frost approaches to know when to cover plants or pick green fruit. It is also useful when hardening off seedlings, so you avoid moving them out on a cold day.
Common mistakes to avoid
- Watching only the daytime high: a warm day with a sub-50°F night still stalls growth.
- Ignoring soil temperature: warm air over cold soil leads to poor rooting after transplant.
- Planting on the first warm day: one mild afternoon does not mean the cold season is over.
- Doing nothing in heat: above 90°F, skipping shade and water causes blossom drop.
- Forgetting frost cover timing: covers must go on before dusk to trap ground heat.
Accuracy and limitations
The checker accurately classifies a temperature you enter, but it cannot see your full local conditions.
What it calculates accurately: the Celsius-to-Fahrenheit conversion and the correct tolerance band for the value.
What it does not account for: soil temperature, humidity, wind, sun exposure, plant age, and how long the temperature lasts. Treat the verdict as guidance and confirm with a soil thermometer and the local forecast.
Methodology
Method: tolerance-band classification of air temperature. Input used: temperature value and unit. Assumptions: bands reflect typical tomato responses; ideal 60–85°F, cold damage below 50°F, frost below 33°F, heat stress above 85°F. Rounding: displayed Fahrenheit rounded to the nearest degree. Edge cases: empty or non-numeric input prompts for a valid number.
Sources: Iowa State University Extension – Growing Tomatoes, The Old Farmer’s Almanac – Tomatoes, Royal Horticultural Society – Tomatoes. Last reviewed: September 24, 2026 · Reviewed by Aiza Anwar.
Frequently asked questions
What temperature is too cold to plant tomatoes?
Do not plant tomatoes when nights fall below 50°F (10°C). Cold soil and air stall roots and delay fruit set.
At what temperature do tomatoes stop setting fruit?
Tomatoes drop flowers and stop setting fruit when daytime temperatures rise above about 90°F (32°C) or nights stay above 75°F (24°C).
Will frost kill my tomato plants?
Yes. A frost at or below 32°F (0°C) kills unprotected tomato plants. Cover them or move containers indoors when frost is forecast.
What is the ideal temperature for growing tomatoes?
The ideal range is 60°F to 85°F (16–29°C), with nights near 60°F giving the best flowering and fruit set.
Can tomatoes recover from cold damage?
Mild chill below 50°F slows plants but they usually recover once it warms. Frost-blackened tissue does not recover, so prune damaged parts.
How do I protect tomatoes from a late frost?
Cover plants before dusk with row covers, buckets, or a wall-of-water to trap ground heat, and remove covers in the morning.
What soil temperature do tomatoes need to be transplanted?
Transplant once soil reaches about 60°F. Warm air over cold soil leads to weak rooting and stalled growth.
Do tomatoes stop growing in extreme heat?
Above 95°F growth and pollination slow sharply. Plants survive with shade and deep watering but set little fruit until it cools.
Is 90 degrees too hot for tomatoes?
Around 90°F is the upper edge of comfort. Fruit set begins to drop, so provide afternoon shade and steady moisture.
Related tomato tools
See the When to Plant Tomatoes guide
This checker provides general gardening guidance for planning, not professional horticultural advice. Temperature bands are typical ranges; confirm soil temperature and the local forecast before planting or protecting plants. Spotted an error? Tell us here.