RS-485, Modbus RTU, one 4-core cable. I’ve wired a few greenhouses like this.
Cable: a shielded twisted pair cable with two pairs, for example a 2x2x0.5 mm². One pair for A/B, the other pair for power: 12 V and 0 V. The 0 V also serves as the RS-485 common. At 80 m and 12 Nanos drawing maybe 40 mA each through a small buck converter, the voltage drop on 0.5 mm² is under a volt, fine for 12 V in.
Topology: a daisy chain along the benches, with short stubs (under 30 cm) to each node. No star. 120 Ω termination at both ends of the main run, bias resistors only once, at the ESP32 end. Each Nano gets a MAX485 (or better, an auto-direction module so you save a pin).
Protocol: each Nano is a Modbus RTU slave with its own address 1-12 (the ModbusRTUSlave library is fine), holding registers for moisture, temp x10, RH x10, lux. The ESP32 is master, polls every node every 30 s at 19200, and publishes:
v1/gw/connect {"device": "bench-03", "type": "greenhouse-node"}
v1/gw/telemetry {"bench-03": {"ts": 1767225600000, "values": {"soil": 41, "t": 23.4, "rh": 71.2, "lux": 8200}},
"bench-04": {"ts": 1767225600000, "values": {"soil": 38, "t": 23.1, "rh": 70.8, "lux": 7900}}}One gateway message for all twelve, and megan_b40 is right about ts, only if the ESP32 has NTP. Make a device profile named greenhouse-node and every child lands in it with the same alarms.
If a node stops answering, publish v1/gw/disconnect for it so it shows offline instead of silently going stale.