ECOWITT WN34BS Soil Temperature Sensor

Before you buy: this probe cannot reach the internet by itself. It only talks by radio to an Ecowitt gateway, so buy it together with one of these:

• If your plot has only cellular coverage and sun: the ECOWITT WittField 4G & Solar Field Weather Station, whose gateway uploads over 4G, runs on solar power and holds up to eight of these probes.
• If a building with Wi-Fi and an outlet is within radio range: the GW1206 Soil Moisture Kit or the Wittboy weather station.

The WN34BS is a soil thermometer with a stainless steel probe of about a foot and a small LCD on top, so you can read it where it stands as well as remotely.

Out in the field. It runs on AA batteries housed in its waterproof head, with no cable to it, so it can stay in a field bed through the season; lithium AAs hold up best through frost. Once paired, its readings come back through Ecowitt's REST API alongside the rest of your data.

Soil temperature decides when seeds germinate and when a bed is ready to plant, which is why Good Earth MCP projects it for planting windows. A probe in your own ground lets you check that projection against what your soil is actually doing.