My nephew recently visited me and asked for advice on lawn irrigation. He has a couple of soil moisture sensors placed all over his lawn in the root zone (about 10 cm deep) and is wondering how to adjust the threshold for irrigation. My first simple advice was just to observe the lawn and identifiy the water content when the leaves are getting brown. Brown leaves are an indication of water stress. My nephew was not really satisfied with this answer and said: "Grandma, you have such a long experience in gardening, you have a so-called green thumb, but I am a real novice. Could you please help me so that even I can adjust he irrigation threshold without observing the leaves". So did a survey and found this guide from the University of Florida on Smart Irrigation This is the sum up of their recommendations:

  • Place the sensor at locations which are representative for the area to be irrigated (see more details about sensor locations in the guide)
  • Burry the sensors in the root zone
  • Carefully install the sensors with no air gaps around the sensor
  • Calibrate the sensor
    • Apply water in the sensor area up to saturation
    • Do not apply water for 24 hours
    • Record the water content which is the threshold value (threshold can be adjusted to 20% lower than this value)

In any case I would always observe the lawn and see if it is in good shape with this irrigation threshold setting.