Averaging Several Analog Inputs Into One with Arduino

I am currently working on a project that involves an automated irrigation system. Essentially I want to have several moisture sensors (say 4 or 5) distributed throughout a garden. When the moisture sensors give the appropriate reading, a sprinkler would be activated and water the plants, until the desired moisture level was attained. Due to powering and money constraints, I would like to use only one sprinkler to water the entire area. However, I still want to use several moisture sensors around the garden. What I wanted to know if, using an Arduino Uno, there was a way to take these 4 or 5 analog inputs from the moisture sensors and average them together (using Arduino code) into one value that represents all 4 or 5 moisture sensors. That way the Arduino could get a "big picture" of the current moisture levels of the entire garden, the sprinkler would only be activated when the collective moisture of the entire area was below a certain point. Any and all answers will be appreciated.
Thanks

Yes, digitize the sensor values and average the results in code. If you want to average the sensors before the Arduino use an OP AMP ADDER configured for a gain of 1/4 or 1/5 and it will output the average of the four or five sensors.

RC filtering before the OP AMP can be used to reduce the system susceptibility to RF (nearby cell phones for example), and a capacitor across the ADDER feeback resistor can make it less susceptible to 50/60 Hz noise.

Could you perhaps provide me with some example code? I am new to programming and would appreciate the help.