I have a number of plants which need watering at different times. I relied on visual aids but wanted something a little more high-tech, so I built this water sensor around a Seeed ESP32-C6 with an 18650 and a HW-390 capacitive moisture sensor. (full BOM in the assembly guide)

You can flash whatever you want to it; I use this code, which was co-authored with Claude AI.

My code enables this to be presented to Home Assistant via MQTT, to create dashboards and automations like alerts

It will start a wifi hotspot on first boot if no config is stored, allowing you to configure it 

Once set up you can later reconfigure most things from HA, for example

• IP configuration
• Pinout
• Set delay-on-first-boot (default 15m - gives you time to get it in the ground before it sends a reading)
• MQTT broker details
• Syslog details
• Reed switch or Hall-effect sensor (if added, can be used to force-boot the device on demand for updates etc)
• Update channel (stable or beta)

You can also 

• reset the config on next boot
• force update on next boot
• reboot the device (deprecated - from earlier revision when it was always-on)

The assembly guide is attached. I'm a very novice builder, so I promise it's easy!