A greenhouse is a wonderful thing, but it is also a temperature trap. On a bright March morning the air inside can climb past 30C while it is still frosty outside, and on a clear night in the same week it can drop close to freezing. If you are raising seedlings, overwintering tender plants or ripening tomatoes, knowing exactly how hot and cold your greenhouse gets is the difference between healthy growth and a tray of collapsed seedlings.
That is why a good thermometer is one of the cheapest and most useful bits of kit you can own. In particular you want a max/min thermometer, which remembers the highest and lowest temperatures since you last reset it, so you can see overnight lows even though you were tucked up in bed. We have used everything from simple capillary dials to smart WiFi sensors, and below we have picked the best greenhouse thermometers you can buy in the UK in 2026, across every budget.
Quick verdict: our top greenhouse thermometers at a glance
If you just want a reliable reading and a record of overnight lows, the Brannan Digital Max Min Greenhouse Thermometer is the sensible default: cheap, humidity-tolerant and easy to read. If you also want to keep an eye on humidity (which matters for damping off and mould), the ThermoPro TP55 adds a hygrometer for a couple of pounds more. And if you would rather check the greenhouse from your kitchen, a wireless sensor like the ThermoPro TP63 or a smart WiFi model such as the Govee Hygrometer Thermometer will send the readings straight to a display or your phone. For traditionalists and unheated allotment greenhouses with no power, a classic capillary max/min thermometer still does the job for under a tenner.
How to choose a greenhouse thermometer
Max/min memory is the feature that matters
Any thermometer tells you the temperature right now, but a greenhouse thermometer worth buying records the maximum and minimum since it was last reset. This is the whole point: it lets you see that your greenhouse dropped to 2C overnight even though it reads 18C when you wander down after breakfast. That overnight low tells you whether your frost protection is working and whether it is safe to move plants out. A simple button resets the memory each morning or evening.
Analogue or digital?
Traditional capillary thermometers use a liquid column and little markers that get pushed up and down, and are read off a printed scale. They need no batteries, never crash and cost very little, which makes them ideal for a cold, unpowered greenhouse. The trade-off is that they can be fiddly to read accurately and the reset uses a small magnet or button. Digital models are easier to read at a glance, usually more precise, and often add humidity, but they rely on a battery that can struggle in a very cold, damp greenhouse. For most people a digital max/min thermometer is the easier choice.
Do you want humidity too?
Humidity is the quiet troublemaker in a greenhouse. Too high and you invite botrytis, mould and damping off among seedlings; too low in summer and plants wilt and red spider mite thrives. A combined thermo-hygrometer shows both temperature and relative humidity on one screen, so you know when to open a vent or damp down the floor. It is a small upgrade that pays off, especially if you propagate.
Wired, wireless or smart?
A basic thermometer lives inside the greenhouse and you read it when you visit. A wireless set has a weatherproof sensor in the greenhouse and a display you keep indoors, so you can check the overnight low without stepping outside on a frosty morning. Smart WiFi models go further and log readings to an app on your phone, with alerts if the temperature drops below a level you set, which is genuinely useful if you are overwintering something precious.
Placement and accuracy
Wherever you buy, remember that placement matters more than the last decimal point of accuracy. Mount the thermometer in shade at plant height, away from direct sun and away from the heater, or it will read the sunshine rather than the air your plants feel.
The best greenhouse thermometers for 2026
1. Brannan Digital Max Min Greenhouse Thermometer – best overall
Brannan is a long-established British instrument maker, and their little green digital max/min thermometer has become the standard recommendation in UK greenhouses for good reason. It shows the current temperature plus the maximum and minimum since the last reset, switches between Celsius and Fahrenheit, and shrugs off the damp conditions that kill cheaper units. It wall-mounts or stands on the staging, runs for ages on a single button cell, and costs around £13. For the overwhelming majority of gardeners this is all the thermometer you need.
Pros:
- Reliable max/min memory with a simple one-button reset
- Copes well with greenhouse humidity where cheaper units fail
- Trusted British brand at a very fair price, around £13
Cons:
- No humidity reading
- Basic display with no backlight for dark winter mornings
2. Traditional Capillary Max Min Thermometer – best budget and no batteries
If you have an unheated greenhouse, an allotment plot with no power, or you simply distrust anything with a battery, a classic capillary max/min thermometer is hard to beat. Two little index markers are pushed up and down by the liquid column and stay put to show the high and low, which you reset with the built-in magnet or button. These mercury-free dials cost around £8 to £12, will outlast most digital units and are completely immune to flat batteries and cold-weather glitches. Reading them precisely takes a moment’s care, which is the only real downside.
Pros:
- No batteries, nothing to crash or fail in the cold
- Very cheap, typically £8 to £12
- Rugged and long-lasting
Cons:
- Harder to read accurately than a digital display
- No humidity, no backlight, no alerts
3. TempPro TP49 Mini Thermo-Hygrometer – best compact option
Sold under the TempPro name (previously ThermoPro), the TP49 is a tiny, inexpensive digital thermometer and hygrometer that is popular for propagators, cold frames and small greenhouses where space on the staging is tight. It shows temperature and humidity with a small comfort icon, and the current readings update quickly. At around £9, or less in a multipack, it is an easy way to add humidity monitoring to a propagation bench. The one thing to note is that it does not hold a formal max/min record, so it is best as a supplement rather than your main overnight monitor.
Pros:
- Very cheap, especially bought as a multipack
- Compact enough for cold frames and propagators
- Adds a humidity reading
Cons:
- No true max/min memory function
- Small display, best read up close
4. ThermoPro TP55 Temperature and Humidity Monitor – best for humidity
The TP55 is a step up in usefulness for a modest extra outlay of around £16. It has a large, clear screen with a backlight, shows temperature and humidity together, and records the high and low from the last 24 hours as well as the all-time max/min. A comfort indicator tells you at a glance whether conditions are dry, comfortable or wet. For gardeners who propagate from seed and want to head off damping off and mould, being able to see both figures on one big display is genuinely handy.
Pros:
- Large backlit display, easy to read across the greenhouse
- Temperature and humidity with 24-hour and all-time max/min
- Still keenly priced at around £16
Cons:
- A bit bulky for a very small greenhouse
- Table-standing design is happier indoors than screwed to a damp frame
5. ThermoPro TP63 Wireless Weather Station – best wireless
The appeal of a wireless set is obvious the first time it is frosty: you check the overnight greenhouse low from the warmth of your kitchen. The TP63 pairs a weatherproof outdoor sensor, which you site in the greenhouse, with an indoor display showing both indoor and greenhouse temperature and humidity, plus max/min for each. Range is good across a normal garden. Expect to pay around £22 to £28. If your greenhouse is at the bottom of the plot, this saves a cold trek every morning and makes it far more likely you will actually keep an eye on things.
Pros:
- Read the greenhouse from indoors, no cold trips outside
- Weatherproof remote sensor with good garden range
- Shows temperature and humidity with max/min for both locations
Cons:
- More expensive than a standalone unit
- Two sets of batteries to keep an eye on
6. Govee WiFi Hygrometer Thermometer – best smart choice
For anyone overwintering tender or valuable plants, a smart sensor is the safety net. Govee’s little WiFi thermo-hygrometer sits in the greenhouse and logs temperature and humidity to an app on your phone, so you can scroll back through the week and, crucially, set alerts that ping you if the temperature falls below, say, 3C. That early warning can save a collection on a night when the heater fails or the forecast turns nasty. It needs WiFi to reach the greenhouse, which is worth checking, and it typically costs around £30 to £40. For peace of mind over winter it is money well spent.
Pros:
- App logging with history and low-temperature alerts to your phone
- Excellent early warning for heater failures and cold snaps
- Compact and easy to place
Cons:
- Needs a WiFi signal that reaches the greenhouse
- The dearest option here, around £30 to £40
Greenhouse thermometer comparison
| Thermometer | Type | Humidity | Max/min | Approx price |
| Brannan Digital Max Min | Digital | No | Yes | £13 |
| Capillary Max Min | Analogue | No | Yes | £8-12 |
| TempPro TP49 | Digital compact | Yes | No | £9 |
| ThermoPro TP55 | Digital | Yes | Yes | £16 |
| ThermoPro TP63 | Wireless | Yes | Yes | £22-28 |
| Govee WiFi Hygrometer | Smart WiFi | Yes | App log | £30-40 |
Getting the best from your greenhouse thermometer
A thermometer is only as good as where you put it. Fix it at plant height, in the shade, and keep it out of direct sun so it reads the air temperature your plants actually experience rather than the glare of the glass. Keep it away from the heater, the door and any vents, where draughts and hot spots will skew the reading.
Get into the habit of resetting the max/min each evening and reading it the next morning; that overnight low is your single most useful figure through autumn and winter. If the low is creeping towards freezing, it is time to add bubble wrap insulation, a greenhouse heater or an extra layer of fleece over tender plants. In high summer, watch the daytime maximum and the humidity, and open vents or damp down the floor before your plants start to suffer.
Frequently asked questions
What temperature should a greenhouse be?
It depends what you are growing. For overwintering most tender plants you want to keep the minimum above about 3C to 5C to stay frost free, while a heated propagator bench for early seedlings is happier around 18C to 21C. In summer, try to keep the daytime maximum below around 30C with ventilation and shading, as very high heat stresses most crops.
Where should I put a greenhouse thermometer?
At plant height, in the shade, away from direct sun, the heater and the door. Mounting it on a north-facing upright or under the staging usually gives the truest reading of the air your plants feel.
Do I really need a max/min thermometer?
For a greenhouse, yes. A plain thermometer only tells you the temperature at the moment you look, which is almost never the moment that matters. The max/min memory captures the overnight low and the midday peak while you are elsewhere, and those two figures are what actually guide your heating, ventilation and frost protection.
Our verdict
You do not need to spend much to take proper control of your greenhouse climate. For most gardeners the Brannan Digital Max Min Greenhouse Thermometer, at around £13, is the sweet spot of price, reliability and ease of use. Add the ThermoPro TP55 if you want to watch humidity as well, step up to the wireless TP63 if your greenhouse is a walk from the house, or go smart with the Govee WiFi sensor if you are overwintering plants you cannot afford to lose. Whichever you choose, once you can see your overnight lows and daytime peaks, you will wonder how you ever gardened under glass without one.
For more on keeping your greenhouse in good order through the colder months, see our guides to the best greenhouse heaters, greenhouse insulation and automatic vent openers.
