Quick answer: Greenhouse strawberries are a cool-season crop. Typical targets are around 18–25 °C by day and 8–13 °C at night, with the root zone around 15–20 °C. Above about 28–30 °C, flowering, pollination and fruit size suffer; cool nights help fruit size and flavour. Short-day (June-bearing) cultivars need short days and cool temperatures to start flowers, while day-neutral cultivars flower more continuously but still slow down in heat. Every temperature move also changes humidity: cooling at night pushes RH up, so plan dehumidification or heat-and-vent with your temperature strategy.
Quick answer (typical ranges; follow your cultivar guidance)
- Day: about 18–25 °C. Night: about 8–13 °C.
- Avoid long periods above about 28–30 °C, especially during flowering.
- Root zone: about 15–20 °C.
Typical temperature targets by stage
| Stage | Day | Night | Notes |
|---|---|---|---|
| Establishment after planting | 18–22 °C | 10–13 °C | Moderate temperatures for root growth |
| Vegetative growth | 18–24 °C | 8–12 °C | Warmer days speed growth; avoid soft, leggy plants |
| Flower initiation (short-day cultivars) | Cool, with short days | Cool, often below about 15 °C | Short-day cultivars initiate flowers under short days and cool conditions |
| Flowering and pollination | 18–25 °C | 8–12 °C | Heat above about 28–30 °C reduces pollen viability and pollinator activity |
| Fruit development and harvest | 18–24 °C | 8–12 °C | Warmer speeds ripening but gives smaller, softer fruit; cool nights improve sugar and firmness |
These are typical ranges from greenhouse strawberry practice. Cultivar trials show how much results vary with cultivar and season; for example, NC State Extension reports greenhouse cultivar performance alongside the environment each crop experienced (NC State Extension), and USDA-ARS has published greenhouse strawberry research under controlled conditions (USDA-ARS).
Root-zone temperature
The root zone often matters as much as air temperature:
- Cold substrate (below about 12 °C) slows root activity, water and nutrient uptake, even when air is warm.
- Hot substrate (above about 25 °C) in sunny tabletop systems stresses roots and raises disease risk.
- Measure substrate temperature in the gutters or bags, not only the air. Shade or white bags reduce overheating; heating pipes near the gutters warm cold roots.
Managing heat without creating humidity problems
| Action | Temperature effect | Humidity effect |
|---|---|---|
| Ventilation | Lowers temperature | Lowers humidity if outside air is drier; raises it in humid weather |
| Shading screens | Lowers temperature | Can trap humid air under the screen at night |
| Fogging or pad cooling | Lowers temperature | Adds water; stop early enough for the canopy to dry before night |
| Night temperature drop | Saves energy, improves fruit | RH rises; condensation risk on flowers and fruit |
| Heating | Raises temperature | Lowers RH but removes no water |
The night drop is where temperature and disease meet: as the house cools from 22 °C to 10 °C, air that was at 60 % RH reaches saturation unless water is removed. That is when gray mold infects flowers. Hold a margin below saturation (for example about 83 % RH at 10 °C) using heat-and-vent or a greenhouse dehumidifier. See how to prevent mold in greenhouse strawberries.
Summer overheating: what a strawberry grower can do
A common problem: commercial strawberry greenhouses overheat in summer, flowering stops and fruit gets small and soft. Work through the options in this order:
| Step | Action | Effect | Watch out for |
|---|---|---|---|
| 1 | Maximise ventilation: roof and side vents fully open, insect screens clean | Often removes the largest share of heat | Screens with fine mesh cut airflow a lot |
| 2 | Shade: shade screen or whitewash, about 30–50 % in peak summer | Cuts solar load directly | Too much shade lowers yield |
| 3 | Evaporative cooling: pad-and-fan or high-pressure fog in dry climates | Cools the air several degrees when outside air is dry | Adds humidity; stop early so the canopy dries before night |
| 4 | Cool the root zone: white bags, shaded gutters, cooled nutrient solution | Protects roots when air control is limited | Measure substrate temperature |
| 5 | Mechanical cooling (heat pumps, chillers, HVAC) | Works in humid climates where evaporative cooling fails | High cost; usually only for high-value or closed houses |
| 6 | Plan the crop: cultivar choice, planting dates that avoid peak heat | Avoids the problem | Market timing |
In humid climates, steps 3 and 5 interact with humidity: an HVAC system for a strawberry house must handle both heat and the moisture from transpiration, which is why closed or semi-closed houses combine cooling with dehumidification.
Day–night transition
- Evening: lower temperature gradually; start moisture removal before the canopy cools.
- Morning: raise temperature slowly so cold fruit and flowers do not collect condensation as warm, humid air reaches them.
- Cloudy days: keep temperature moderate and air moving; transpiration is low and the canopy stays humid.
Diagnosing a temperature problem
- Measure canopy air temperature and RH at fruit height, in shade, in several zones.
- Measure substrate temperature at the same time.
- Record heating, vents, screens, fogging and irrigation on the same timeline.
- Compare symptoms (small fruit, poor fruit set, soft fruit, slow growth) with the period they started.
- Change one control at a time and record the result.
Equipment for temperature and humidity
- Heating: pipe heating near the crop and gutters gives even temperatures; hot-air heaters dry the air but heat less evenly.
- Cooling: ventilation and shading first; pad or fog cooling in dry climates.
- Dehumidification: for humid nights when venting loses too much heat or the outside air is humid; refrigerant units return the heat of condensation to the house.
- Air movement: horizontal airflow fans keep temperature even and flowers dry.
See how to choose a greenhouse dehumidifier and the VPD chart.
FAQ
Frequently asked questions
What is the best temperature for strawberries in a greenhouse?
Typically about 18–25 °C during the day and 8–13 °C at night, depending on cultivar and stage.
How hot is too hot for greenhouse strawberries?
Long periods above about 28–30 °C reduce flowering, pollination and fruit size.
Do strawberries need cold nights?
Cool nights improve fruit size, firmness and flavour, and short-day cultivars need cool, short days to start flowers.
Do strawberries need low or high humidity?
Moderate: about 60–80 % RH during the day, with flowers and fruit kept dry at night; long periods near saturation favour gray mold.
How do I stop a strawberry greenhouse overheating in summer?
Ventilate fully, shade 30–50 % in peak sun, use evaporative cooling in dry climates, cool the root zone, and consider mechanical cooling only for closed or high-value houses.
How does temperature affect strawberry humidity?
Cooling raises RH without adding water. A night temperature drop can push the house to saturation unless moisture is removed.
Sources
- NC State Extension, Greenhouse strawberry production: report of cultivar performance 2022–2023.
- USDA-ARS, Agricultural Research magazine (1998), greenhouse hydroponic strawberry research.
- UMass Extension, Reducing humidity in the greenhouse.
