My wife and I transformed the (rather) small yard in front of our house into a flower garden. It is full of roses, lavender, tulips, dahlias, and shrubs. The open areas are covered in bark chips to keep down the weeds.
To make sure that the flowers stay properly watered, I put some Bluetooth capable sensors out in critical spots in the yard.
To my surprise, it turned out that I hardly need to water things at all - or do I? Some times the moisture is at the low end of the suggested range, and stays there for hours. Is that bad? Did it maybe drop below the recommended levels at some times and places? I don't know, but I want to find out for sure.
The sensors in the critical spots seem to show that there's always enough water in the soil under the 4 inches of bark that I didn't need to water things at all.
The soil moisture varies over the course of the day. The soil dries out somewhat during the day and recovers during the night.
During the driest part of the day, the sensors showed that the flowers still had enough moisture available - if the charts provided by the sensor manufacturer can be trusted and if the measured spots truly represent the state of the whole garden.
The handful of sensors I used couldn't give me a very detailed picture of the situation. I tracked things as well as I could with the original software from the sensor manufacturer, and cursed it every day.
The software is only intended to track the moisture and nutrients for single plants - it cannot combine data from multiple sensors.
Even for a single sensor, it has painful limits. You can't display the last 30 days so that you can track things easily. Nope. It only shows you the last month - on the first of the month you have an empty chart.
I started planning a better system with my own software.
The current idea is to space sensors on a 1 meter grid through the front yard (and selected spots in the backyard) to provide a comprehensive picture of just what the water in the dirt is doing.
The sensors will monitored by several solar powered ESP32 modules which will transmit the collected sensor data via WiFi and MQTT to a Django program on a Raspberry Pi.
I want to generate an animated "heat map" style chart of the soil moisture to see how it develops over the entire spring and summer, and I want to use the daily charts to tell when (or if) I need to water things.
Do yourself the favor and check out capacitive soil moisture sensors. There is a clone of the official chirp from catnip electronics for a lot less on aliexpress. I didn't feel guilty since I already bought a whole bunch of sensors from them. I used a special coating for the sensor but it should be possible to use nail polish. The xiaomi things just seem to use a galvanic measurement so you can't use fertilizer and those electrodes will rot away. I tried it back then with dirt cheap sensors and two steel nails as electrodes.
The good thing about their sensor is that you can go into deep sleep with it.