You may be interested in this ultra low power remote temperature+ sensor I built. I calculate that it draws about 65 uA on average from a Lipo battery, reports temperature, humidity and pressure over a distance of at least 100 ft.
The remote hardware is based on Moteino M0 with a BME280 sensor and RFM69 radio soldered on the Moteino modules. No extra wiring is required. The Arduino code is here.
It sleeps 5 minutes between measurements to save power. For other applications like a remote contact sensor (burglar alarm) the code could be modified to wake up the CPU and transmit on an external interrupt.
I used a ESP8266 and a RFM96 radio module to built a MySensors gateway using MQTT over Wifi to Hassio. The Arduino code is from a fairly standard example. I used a dipole antenna from lowpowerlab to get good radio range. The Gateway runs off an AC power adapter in the house.
If I had a greenhouse, I would want to automate more. I would want to turn on a fan, open a vent and irrigate. That would require running AC power to the greenhouse and eliminate the need for battery operation. The RFM69 radio is still useful because of its superior range when compared to WiFi. Around my house, I still prefer my AC powered WiFi IOT modules as they don’t have to go through the MySensors Gateway.