Garden Highpro Thermo-Hygrometer Basic

A digital meter showing temperature and humidity at once, with a memory for the highest and lowest reading. Stand it or hang it.

The Garden Highpro Thermo-Hygrometer Basic is the entry model: a large LCD, two values on screen, and a min/max memory so you also see what happened while you were away. Range 0 to 50 °C and 25 to 90% relative humidity, on a single AAA battery.

What humidity actually tells you

Everyone understands temperature. Humidity is the number most often misread, and it drives more than most growers realise.

What you measure is relative humidity: how much water vapour is in the air, as a percentage of the most that air could hold at that temperature. That word "relative" is the whole trap, because warm air can hold far more moisture than cold.

The consequence: the same amount of water in the air gives a different percentage as soon as the temperature changes. If your tent cools overnight from 26 to 20 °C without a single drop being added, relative humidity climbs sharply. That is precisely why mould almost always strikes at night, and why a daytime reading tells you little about your actual risk.

Why it matters to your plants: a plant evaporates water through its leaves, and that evaporation is the engine driving water and nutrient uptake from the roots. If the air is already saturated, the plant cannot shed its water and that flow stalls: the plant sits in a humid room and still grows slowly. If the air is very dry, it evaporates faster than it can resupply, closes its stomata, and growth stops as well.

Which is why you always read both values together. Separately they say little.

Technical Specifications:

• Measures: temperature and relative humidity, simultaneously
• Temperature range: 0 to 50 °C
• Humidity range: 25 to 90% RH
• Memory: highest and lowest recorded values
• Display: large LCD, readable from a distance
• Placement: free-standing or wall mounted
• Battery: 1 x 1.5 V AAA (included)

Frequently asked questions

What humidity should I aim for?
It shifts with the stage: cuttings and young plants want it more humid, in flower you bring it down to avoid mould. More important than a single target is knowing your night-time peak, that is where your risk sits.

Why does my humidity climb at night when I change nothing?
Because the temperature falls. Cooler air holds less moisture, so the same water gives a higher percentage.

Where should I hang it?
At canopy height, out of direct lamp light and not right in front of a fan. On the wall by the door you are measuring the corridor, not your plants.

What is the difference from the Medium and Premium?
Those have a remote sensor on a 1.5 metre cable, so you read temperature in two places at once. The Premium also has a larger display.