I’m trying to get readings from my Grow hats and send them to Home Assistant for display in pretty graphs. For those of you who don’t use HAss, if you send it any data but don’t specify the units, it assumes it’s a string.
Saturation appears to be a percentage. Moisture just seems to be a number that doesn’t have a range - taking a sensor out of the soil and putting it straight in to water doesn’t make the readings go from 0 to 100, for example.
Can anyone confirm that Saturation is a percentage and what Moisture is actually measuring? Bonus question - if Moisture is, for example, measuring resistance can I convert it to a number that represents something gardening related? Or does anyone know where I can learn what that number represents for my soil quality etc so I can figure the rest out myself?
Hi Steve,
It‘s quite complicated with the actual moisture value and unit.
Normally you should need to calibrate the sensors to have really accurate values as relative humidity (%rH).
Therefore you normally need to do the following:
Have one pot with the soil dried for multiple hours (3-4) in the oven (don‘t forget to remove the plants out of the soil before ;))) ) —> this will be your 0%rH reference data
put the sensor into that dry soil and remember the value (best practice to run a series of sensor readings and calculate the avg value)
now put as much water to the soil as possible and wait a bit so that no more remaining water is coming out of the pot —> this is your 100% reference data
put the sensor into that wet soil an remember the value (here also the avg of a test series is more accurate)
Now with a little math (assuming that the capacity is a linear function) you can correct the 100% Value by subtracting the 0% value. And all values in between are now direct %rH values.
But - this is only an approximation because there are many influencing factors like temperature and soil composition. Furthermore this is required every time you change the pot (and so the soil mixture will change).
I‘ve found an article in the internet that the described approach will be used in agriculture but for home use it is usually too much effort!
I assume that this is the reason why Enviro Grow does go the easy way to simply compare the direct measured capacity values with the previous ones in order to determine whether watering is required or not!
(Before receiving my Enviro Grow I made a lot of research of how to realize such a calibration and have experimented with an older Pico and a moisture sensor; and then I noticed that the pre-installed solution is more than sufficient for me!)
Hope this helps!