The most important sensor for our system is soil moisture which is needed in order to provide a number of key features. Soil moistures can come in a few different models. The cheaper varieties can not be as accurate and easily get suffer from corrosion. I recommend getting a capacitive soil sensor.
The moisture sensor will give you a reading from 0 - 1024 which is the resistance. A lower reading of resistance in our case usually means more moisture present. Not every soil sensor will give the exact same results event given the same conditions. Therefor you should do some small calibration tests with your sensor using dry soil and a cup of water to determine the extremes of the measurements.
[Integer] 0 - 1024
Here are some readings from my actual setup I used to help calibrate my readings. Use them as a reference to get started but I suggest do your own tests for ideal results.
|Very Dry Soil (Cracking)||515|
|Way Oversaturated Soil||250|