The best type of thermometer for a greenhouse is a digital thermometer with a hygrometer (temperature + humidity sensor), ideally with min/max recording.

Greenhouses are sensitive environments where both temperature and humidity affect plant growth, so a combined thermometer-hygrometer provides a more complete and accurate picture.

A standard thermometer only measures temperature, but in a greenhouse:

- Humidity directly affects plant health and disease risk
- Temperature and humidity work together to influence growth
- Poor humidity control can lead to mould, mildew, or poor germination

A thermometer with a hygrometer allows you to monitor both factors at the same time, making it far more useful than a temperature-only device.

Greenhouse thermometers should be placed in the shade, not in direct sunlight.

Direct sun will artificially heat the thermometer, causing it to display a temperature that is much higher than the actual air temperature inside the greenhouse. For accurate readings, the thermometer must measure the ambient air temperature, not solar radiation.

Sunlight can significantly distort temperature readings because:

- The thermometer absorbs radiant heat directly
- Readings can be several degrees higher than actual conditions
- It does not reflect the temperature your plants are experiencing

This leads to misleading data and can result in poor decisions around ventilation, watering, or shading.

For the most accurate results, place your thermometer:

- In a shaded area within the greenhouse
- At plant height (where temperature matters most)
- Away from glass panels, heaters, and vents
- In a position with good air circulation

This ensures you are measuring a true representation of the growing environment.

The ideal temperature for a greenhouse is typically 18°C to 24°C during the day and 10°C to 15°C at night, depending on the plants being grown.

This range supports healthy growth for most common plants, including vegetables, seedlings, and ornamental plants. Keeping temperatures within this range helps optimise photosynthesis, nutrient uptake, and overall plant development.

Temperatures above 30°C are generally considered too hot for most greenhouse plants.

Excessive heat can:

- Stress plants and slow growth
- Increase water loss and wilting
- Reduce fruit set in crops like tomatoes and peppers
- Encourage pests and diseases

In hot weather, ventilation, shading, or cooling systems may be needed to maintain safe conditions. Temperatures below 5°C can be harmful to many plants, especially tender varieties.

Risks of low temperatures include:

- Frost damage or plant death
- Stunted growth
- Reduced germination rates

For frost-sensitive plants, maintaining a minimum of 10°C or higher is usually recommended.

Yes, different plants have different optimal temperature ranges:

- Seedlings and propagation: 20°C to 25°C
- Tomatoes, cucumbers, peppers: 18°C to 24°C
- Hardy plants and overwintering: 5°C to 10°C

Understanding your specific crops is key to maintaining the correct environment.

The main difference between digital and dial garden thermometers is how they measure and display temperature.

Digital thermometers use electronic sensors and show readings on a screen
Dial thermometers use mechanical components (like bimetal coils or liquid expansion) and display readings on a circular scale

Digital models are generally more precise and easier to read, while dial thermometers are simpler, durable, and don’t require power. Digital thermometers are usually more accurate and precise than dial thermometers.

- Digital models often display readings to 0.1°C resolution
- Dial thermometers typically have broader scale increments and lower precision

However, accuracy depends on quality, some digital models may still vary by ±1°C or more, despite showing very precise numbers