Tomato fruit set fails when night temperatures persistently exceed ~21 °C
Tomato fruit set fails when night temperatures persistently exceed ~21 °C (70 °F); high day temperatures above 29-32 °C (85-90 °F) compound it.
As recorded: Tomato fruit set fails when night temperatures persistently exceed ~21C (70F); high day temperatures above 29-32C (85-90F) compound it.
Well established A person has checked it against its sources. If you skip this, you lose real yield. The planner warns you.
How it works
Sustained high day (>29-32 °C / 85-90 °F) and night (>21 °C / 70 °F) temperatures make pollen non-viable ("tacky") and impair its release; flowers go unfertilized within their ~50-hour window and abscise.
What to do about it
Wait it out. Fruit set resumes on its own once nights cool, and the plants make up the gap. Do not reach for shade cloth. It cools the day, and this failure is driven by the night temperature, which Missouri IPM says shading will not touch. If hot nights are normal where you garden, buy a heat-set cultivar next season.
The evidence
Evidence: checked against 2 sources in the research-based literature.
The 2 sources
When daytime temperatures exceed 85 degrees F or nighttime temperatures exceed 70 degrees F, pollination suffers due to pollen becoming "tacky" and non-viable.
Daytime highs of 90° F and above and nighttime lows only getting down to 70° F ... will cause blossom drop and fruit abortion in tomatoes.
Plants it applies to · 1
Read next
How this rule has changed
Every change is dated, newest first. The full record, with each reason, is in the data download.
- Details updated
- Sources updated
- Details updated
- Wording made clearer
- Advice on what to do added
- A person read the sources and confirmed it
- Added to the rules
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Milpa Gardens. “Tomato fruit set fails when night temperatures persistently exceed ~21 °C (70 °F); high day temperatures above 29-32 °C (85-90 °F) compound it.” Evidence grade: Well established. https://milpa.garden/rules/tomato-fruit-set-fails-when-night-temperatures/
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