Heating

The UK’s Best Greenhouse Thermometers For Monitoring Internal Temperatures

thermometer with greenhouse plants in background
Written by April Foot

Greenhouses help to provide plants with the light and warmth they need to grow – but thanks to their transparent walls, the internal temperature can fluctuate massively, depending on the weather.

To make sure you’re not cooking or freezing your plants, it’s a good idea to have a thermometer in your greenhouse.

Greenhouse thermometers monitor the internal temperature of your greenhouse. They differ to regular thermometers in that they also record the maximum and minimum temperatures over a 24-hour period. This means you can see how hot and cold your greenhouse is getting, even when you’re not there to observe the thermometer.

The perfect internal temperature for your greenhouse will vary depending on the type of plant you’re growing, but as a general rule, it should be somewhere between 26°C – 30°C. If the temperatures are too high or low, you can take steps to ventilate or insulate the greenhouse, to adjust the temperature.

If you’re looking for a way to monitor the climate inside your greenhouse, check out our list of the 5 best greenhouse thermometers.

Our #1 Top Pick
Max Min thermometer with internal temperature sensor
Value Pick
Digital Max Min Thermometer - Monitor Max and Min Temperatures With This Handy Greenhouse...
Also Consider...
ThermoPro TP55 Digital Indoor Hygrometer Thermometer Temperature and Humidity Monitor Room Moisture...
Design
Digital
Digital
Digital
Temperature Range
-40 to 40 °C
-10 to +50°C
-50 to 70°C
Humidity Readings
No
No
Yes
Price
Price not available
£9.25
Price not available
Our #1 Top Pick
Max Min thermometer with internal temperature sensor
Design
Digital
Temperature Range
-40 to 40 °C
Humidity Readings
No
Price
Price not available
Value Pick
Digital Max Min Thermometer - Monitor Max and Min Temperatures With This Handy Greenhouse...
Design
Digital
Temperature Range
-10 to +50°C
Humidity Readings
No
Price
£9.25
Also Consider...
ThermoPro TP55 Digital Indoor Hygrometer Thermometer Temperature and Humidity Monitor Room Moisture...
Design
Digital
Temperature Range
-50 to 70°C
Humidity Readings
Yes
Price
Price not available

Last update on 2020-10-27 / Affiliate links / Images / Pricing from Amazon Product Advertising API

We’ve chosen these models for their usability, readability, and value for money. Your plants would definitely thank you, if they could.

Best Pick: Max Min Thermometer

Our favourite greenhouse thermometer is accurate, and the ideal blend of old and new

The Max Min Thermometer from ETI Ltd is our top pick of greenhouse thermometers, thanks to the way it perfectly combines classic and modern styles of thermometer, into an option that will please everyone.

The maximum and minimum temperatures are displayed on traditional-style bar graphs, whilst the current temperature appears numerically on the LCD screen at the bottom. It records temperatures from -40°C to 40°C to an accuracy of ± 1°C, and with a resolution of 0.1°C.

If you prefer to use Fahrenheit, the reading can be switched between °C and °F, with the simple push of a button, and if you want to reset the maximum and minimum readings, there’s a button for that too. The thermometer is free from mercury, which makes it more environmentally friendly.

The thermometer is easy to set up, and use. There’s a built-in hanging slot to make it easier to hang the instrument on the wall in your greenhouse. The thermometer requires 1 x AA battery to work, which is included, so you’re ready to go, straight from the box.

Some might argue that the bar graphs mean the maximum and minimum temperatures are not as easy to read at a glance as the current temperature, but we think this could also be seen as an advantage, as it stops the reader being overwhelmed with numbers – plus, it gives it a nostalgic feel. Overall, this is an excellent greenhouse thermometer, for new and veteran greenhouse owners alike.

Pros

  • Combines old and new technology/displays.
  • Accurate to ± 1°C.
  • Environmentally friendly – free from mercury.
  • Easy to reset, or switch between °C and °F.
  • Built-in slot for easy hanging.

Cons

  • Bar graphs can be more difficult to read at a glance than numerical readings.
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Value Pick: Thermometer World Max Min

Our best value greenhouse thermometer has a clear digital display

If you think you might prefer an entirely numerical display, this Digital Max Min Thermometer from Thermometer World might be a better choice for you.

This one has an entirely digital display, with the maximum and minimum temperatures displayed above and below the current temperature, which is slightly larger, to make it easy to distinguish at a glance. It’s powered by 1 x AAA battery, which is included.

The temperature range of this one is -10°C to 50°C – however, there are some reports of the thermometer malfunctioning at temperatures above 40°C, and -10°C might not be low enough for winters in some places, so it’s probably not the best choice if you live in an area that experiences extremes of temperature.

The design of this thermometer includes a roof, to help protect the screen. However, although the manufacturer says it’s suitable for both indoor and outdoor use, it isn’t fully waterproof, so if you did want to use it outside, make sure to choose a sheltered position – and if using in your greenhouse, make sure not to get it too wet when watering.

Ultimately this is another great greenhouse thermometer, that’s perfect if you live in a relatively mild climate, and want your temperatures displayed on a clear screen in digital format.

Pros

  • Clear digital display for all measurements.
  • Accurate to ± 1°C.
  • Roof to protect it from the elements.
  • Suitable for indoor and outdoor use.
  • Easy to reset, and switch between °C and °F.
  • A hole at the top for easy mounting.

Cons

  • Only records temperatures down to -10°C, which may not be enough in colder areas.
  • Although advertised for outdoor use, it is apparently not waterproof.
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ThermoPro TP55 Digital

This ultra-modern thermometer will also tell you the humidity level of your greenhouse

Prepare to be impressed; this ThermoPro TP55 Digital Thermometer is so much more than just thermometer. As well as the current, maximum and minimum temperatures, this one also tells you the same measurements for humidity, so you can get a clearer picture of the internal conditions of your greenhouse and make any necessary adjustments promptly.

All readings are displayed on the super-modern LCD screen, which is backlit for easy reading and features a touch screen for simple operation. It has an impressive temperature range of -50°C to 70°C, so it should be able to accurately report in all conditions, and you can switch from °C to °F if you prefer.

The humidity range is 10% – 99% and the device also advises whether the shown rating is considered wet, dry or comfort. Note that as this is primarily intended as a home monitoring system, the comfortable humidity range is aimed at humans, and may not reflect the ideal humidity range for your plants – some research may be required.

This thermometer can be wall-mounted, placed on a tabletop using the attached stand, or fixed to a magnetic surface with the built-in magnetic backing. It’s powered by 2 x AAA batteries, which are included.

Although this is the priciest option on our list, when you take into account the stylish, modern design and all the in-built features, we still think it’s great value – and it’s much more than just your average greenhouse thermometer.

Pros

  • Large 4” backlit LCD display is easy to read.
  • Impressively large temperature range.
  • The touch screen offers simple operation.
  • Also measures humidity, as well as temperature.
  • Displays trends, so you can react in plenty of time.
  • Multiple mounting options.
  • Accurate to ± 1°C.

Cons

  • Priciest option on our list.
  • Designed to monitor the home environment – not necessarily intended as a greenhouse thermometer.
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Brannan Digital Max Min

This simple digital thermometer is suitable for both indoor and outdoor use

If you’re looking for a thermometer that is designed for use in the garden or greenhouse, check out this option from Brannan.

This one can be used indoors or outdoors and is advertised as dust-tight and water-resistant. It consists of a green ABS case, with a large display that’s easy to read at a glance, and tells you the current, maximum and minimum temperatures, in a digital format.

The temperature range it can record is -10°C to 50°C, with a 0.1°C resolution, which will be fine for most users, but again might not be enough for more extreme climates. The instrument is accurate to ± 1°C.

Setting up this greenhouse thermometer is simple – you just need to insert the required 1 x AA battery, which is included, and you’re ready to go. If you want to change the temperature from °C to °F, or reset the maximum and minimum records, this is easy to do with the push of a button.

The built-in slot at the top allows you to easily hang it on the wall of your greenhouse. This greenhouse thermometer is simple but effective.

Pros

  • The large, clear digital display is easy to read.
  • Suitable for indoor and outdoor use.
  • Easy to reset and change from °C to °F.
  • Accurate to ± 1°C.
  • Keyhole slot at the top for easy wall mounting.

Cons

  • Temperature range might not be large enough for more extreme climates.
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Outback Blue Greenhouse Thermometer

An easy-to-read thermometer with a large temperature range

Our final greenhouse thermometer comes from Outback Blue. This is another easy-to-use thermometer that tells you the current temperature, as well as the maximum and minimum since the last reset. Resetting it is simple – just press one of the two buttons on the front (the other button is used to change from °C to °F).

This thermometer has an impressively large temperature range of -50°C to 70°C, which is matched only by the ThermoPro on this list and means you shouldn’t ever have a problem with the thermometer not being able to accurately record readings. Temperature recordings are displayed in large text on the LCD screen, so they’re easy to read, even at a glance.

The shell is made from weather-resistant plastic and is suitable for indoor or outdoor use – although if using it outdoors, you must choose a sheltered location, as it is not completely waterproof. The thermometer can be wall-mounted, using the hole at the top of the instrument.

Overall, this greenhouse thermometer is another solid choice, and perfect if you live in an environment that’s likely to experience more extreme maximum and minimum temperatures.

Pros

  • Easy-to-read LCD screen.
  • Large temperature range of -50°C to 70°C.
  • Easy to reset and change from °C to °F.
  • Weather-resistant plastic construction.
  • Slot for easy wall-mounting.

Cons

  • May need a non-standard battery in the event of very low temperatures.
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What Is The Ideal Temperature For A Greenhouse?

The ideal temperature to keep your greenhouse at depends on what you’re growing in it – different plants have different optimum growing temperatures, and different tolerances. For example, tomato plants are heat-tolerant and can continue to grow in temperatures up to 35°C.

Meanwhile, other plants, such as lettuce and cauliflower, are more heat-sensitive and will start to wilt and cease growing at temperatures above 30°C – or lower if the humidity is high too. As a general rule, the ideal temperature for most greenhouses falls somewhere between 26°C and 30°C.

How To Regulate Greenhouse Temperatures

If your greenhouse is too hot or too cold, there are plenty of steps you can take to regulate the internal temperature.

To increase the temperature in your greenhouse, which might be necessary during winter and the less-sunny months, you can use some form of heater. One of the most fuel-efficient options is an electrical heat pad, which is placed under your plants, to heat them from below. By coming into direct contact with the plant, less heat is dissipated into the air and wasted, than if you were to use a heater to increase the temperature of the whole room.

If your greenhouse is too hot, as can occur in summer and on days with lots of sunlight, you can bring the temperature down by using a ventilating system, to improve airflow. The ideal solution is an automatic air vent, which makes use of a piston to push the vent open when the temperature gets too hot and closes when it’s too cold. A fan in the greenhouse will also increase airflow, which will also help to prevent mould and other problems with your plants.

Another method is to hose down the surfaces in your greenhouse, to create an evaporative cooling effect as the water evaporates. For more severe heat, an evaporative cooling machine or mist system will work like an air conditioning unit to drastically decrease the temperature in the greenhouse, and further help to stave off disease.

As high internal temperatures are a direct result of sunlight streaming through the transparent glass, you could also hang cloth or netting over the glass, to block the sun and create shade. The advantage of this eco-friendly method is that it doesn’t require power or involve any on-going running costs.

About the author

April Foot

April is a freelance writer who specialises in travel, home and garden design, and the environment. She is an avid wildlife-enthusiast and adventure-seeker, and feels happiest when in the Great Outdoors.

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