Polytunnel Temperature Data Logger Uk

Direct answer: a polytunnel temperature data logger helps when one thermometer is no longer enough. In a UK tunnel, crop-height air, the high warm layer near the roof and the root-zone or soil-surface area can tell different stories, especially on spring frost nights and hot summer afternoons.

The three positions worth measuring first

Start with plant-level air because that is what tender growth experiences. Add a high-level air probe because polytunnels can trap heat above the crop even when leaves feel cooler. Use the third or fourth channel for soil surface, pot bench level, or the coldest corner near a door. UK polytunnel guidance commonly recommends monitoring more than one point and recording readings to spot trends, which is exactly where a logger beats occasional glances at a dial.

A 48-hour baseline

Log one full day and one full night before changing anything.
Keep doors, vents, fleece and heaters in their normal routine.
Note exact times when you open vents, water plants or add fleece.
Review the lowest pre-dawn reading and the highest mid-afternoon reading.
Move only one variable next: vent timing, fleece layer, shade, heater position or door practice.

What the curve can tell you

A frost problem often shows as a sharp dip just before sunrise, not as a whole cold night. A heat problem often appears as a short spike after the sun reaches the tunnel but before anyone opens vents. The value of a logger is that it makes those hidden windows visible, so you are not redesigning the whole tunnel around the one time of day you happened to check.

Where this approach stops

This is temperature logging only. It does not measure humidity, vapour pressure deficit, soil moisture or automate vents. Commercial growers who need remote alerts, climate control, irrigation integration or crop-yield analytics should specify a horticultural control system rather than a simple thermocouple logging setup.

Reader decision

Use a logger if your next decision is practical and local: when to vent, where frost settles, whether fleece is helping, or whether a seedling bench runs colder than the rest of the tunnel. Do not buy one expecting it to become a greenhouse controller.