Tomato flowers set fruit only within a temperature window. When daytime highs climb above about 90°F, or nights stay above 75°F or drop below 55°F, blossoms often drop without making tomatoes. Enter your daytime high and nighttime low to see whether your plants can set fruit right now.
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What Your Result Means: the verdict shows whether your day and night temperatures fall in the range where tomato flowers pollinate and set fruit. Blossom drop from heat or cold usually corrects itself once temperatures return to the ideal window, so it is rarely a plant health problem.
Why Won’t My Tomatoes Set Fruit?
Most often, the weather is outside the fruit-set window. Enter the daytime high and the nighttime low, and the tool checks both against the ranges tomatoes need to pollinate. It tells you whether conditions are good, too hot, or too cold for setting fruit.
- Enter the Daytime High, the typical afternoon temperature during flowering.
- Enter the Nighttime Low, since warm or cold nights are a common cause of blossom drop.
- Read the Verdict, then wait out the weather or use the tips to keep fruit setting.
What Each Result Means
| Result | What It Tells You |
|---|---|
| Verdict | Whether flowers can set fruit at these temperatures |
| Day and night check | Which temperature is out of range, if any |
| Tip | What to do while you wait for better weather |
Fruit Set by Temperature
The ranges tomatoes need for good pollination and fruit set. Both day and night matter.
| Condition | Daytime High | Nighttime Low | Result |
|---|---|---|---|
| Ideal | 70 to 85°F | 59 to 70°F | Good fruit set |
| Borderline | 60 to 69 or 86 to 90°F | 55 to 58 or 71 to 75°F | Patchy set |
| Hot days | 90 to 95°F | — | Pollination drops |
| Very hot | above 95°F | above 75°F | Blossom drop likely |
| Cool nights | — | below 55°F | Poor set, some drop |
| Cold | below 60°F | below 50°F | Little or no set |
How Does the Check Work?
The tool compares your day and night temperatures with the tomato fruit-set window and returns the limiting condition, hot or cold, that is holding back pollination.
Too hot: day above 95°F or night above 75°F
Warm caution: day above 90°F
Cool caution: night below 55°F
Too cold: day below 60°F or night below 50°F
Borderline: day 60 to 69 or 86 to 90°F, or night 55 to 58 or 71 to 75°F
Tomato pollen becomes sticky and unviable in high heat, and cold nights slow pollination, so both extremes cause flowers to drop before a fruit forms.
Worked Example
Say a summer heat wave brings a daytime high of 96°F and a nighttime low of 78°F. Both are outside the window, so the tool reports blossom drop is likely and suggests shading the plants and waiting. At a mild 82°F day and 62°F night, the same plants sit right in the ideal range for good fruit set.
Factors That Change Fruit Set
- Daytime heat: above about 90°F pollen viability falls, and above 95°F set often stops.
- Nighttime temperature: nights above 75°F or below 55°F both cause blossoms to drop.
- Humidity: very dry or very humid air keeps pollen from moving from flower to flower.
- Variety: some heat-set and cold-set varieties hold fruit through wider swings.
- Plant stress: drought, over-fertilizing with nitrogen, or lack of airflow reduce set even in good weather.
Understanding Your Outputs
| Output | Meaning | Best Used For |
|---|---|---|
| Verdict | Overall fruit-set outlook | Knowing if weather is the cause |
| Day check | Whether the high is in range | Deciding to shade plants |
| Night check | Whether the low is in range | Explaining sudden blossom drop |
| Tip | Next step while you wait | Keeping fruit setting |
When to Use It
Use it when flowers are dropping without setting fruit, during a heat wave or a cold snap, or when choosing varieties for a hot or short-season climate. Pair it with the problem diagnosis tool and the shade cloth calculator for heat.
Common Mistakes to Avoid
- Blaming the plant: weather-driven blossom drop is normal and corrects itself; the plant is usually healthy.
- Over-fertilizing: too much nitrogen pushes leaves over flowers and lowers set.
- Ignoring nights: a warm night can stop set even when the day feels fine.
- Heavy watering swings: drought stress during flowering drops blossoms; keep moisture even.
- Giving up too soon: set usually resumes within a week or two once temperatures return to the window.
Accuracy and Limitations
These are general temperature thresholds for tomato fruit set.
What It Calculates Accurately: whether your day and night temperatures fall inside the typical fruit-set window.
What It Does Not Account For: humidity, variety differences, plant stress, or brief spikes. Treat it as a weather check, not a diagnosis of plant health.
Methodology
Method: daytime high and nighttime low are compared with the tomato fruit-set temperature window, and the limiting condition is reported. Inputs Used: daytime high, nighttime low, and unit. Thresholds: ideal day 70 to 85°F and night 59 to 70°F; too hot at day above 95°F or night above 75°F; warm caution above 90°F day; cool caution below 55°F night; too cold at day below 60°F or night below 50°F; borderline (patchy set) at day 60 to 69 or 86 to 90°F, or night 55 to 58 or 71 to 75°F. Logic: the coldest or hottest limiting factor sets the verdict. Note: humidity, variety, and plant stress also affect set.
Sources: Iowa State University Extension – Growing Tomatoes, The Old Farmer’s Almanac – Tomatoes, Royal Horticultural Society – Tomatoes. Last reviewed: September 25, 2026 · Reviewed by Aiza Anwar.
Frequently Asked Questions
Why are my tomato flowers falling off without making fruit?
This is blossom drop, and it is usually caused by temperatures outside the fruit-set window: days above 90°F, or nights above 75°F or below 55°F. It also follows drought stress or too much nitrogen. Set usually resumes once the weather settles.
What temperature is best for tomato fruit set?
Daytime highs of about 70 to 85°F with nighttime lows of 59 to 70°F give the best pollination and fruit set.
Can it be too hot for tomatoes to set fruit?
Yes. Above about 90°F pollen viability drops, and above 95°F, especially with warm nights above 75°F, flowers often fall without setting fruit.
Do cold nights stop tomatoes from setting fruit?
Yes. Nights below 55°F slow pollination and cause some blossom drop, and below 50°F fruit set is poor. Warmth returns set once nights warm up.
How can I help tomatoes set fruit in a heat wave?
Provide afternoon shade, keep soil evenly moist, avoid high-nitrogen feeding, and choose heat-set varieties. Gently shaking flowering trusses can also help pollen move.
Do tomatoes need bees to set fruit?
No. Tomatoes are self-pollinating; wind and movement shake pollen within each flower. Bees and a gentle daily tap can improve set, but they are not required.
Why do my tomatoes flower but never fruit?
Usually weather outside the fruit-set window, but also heavy nitrogen, drought stress, or very high or low humidity. Check the day and night temperatures first with this tool.
Will blossom drop damage my plant?
No. Blossom drop is a response to weather or stress, not a disease. The plant stays healthy and sets fruit again when conditions improve.
Does humidity affect tomato fruit set?
Yes. Very dry air makes pollen too powdery to stick, and very humid air makes it clump, so both extremes lower set even when temperatures are ideal.
Related Tomato Tools
Size Shade Cloth with the Shade Cloth Calculator
This tool checks weather conditions against typical tomato fruit-set temperatures. It is a guide, not a diagnosis of plant health. Humidity, variety, and plant stress also affect fruit set. Spotted an error? Tell us here.