Reotemp 24 Inch Soil Moisture Meter - Professional Compost & Garden Moisture Tester for Plants, Farms, Lawns | Perfect for Indoor/Outdoor Gardening, Composting & Agriculture

This is a wonderful product! It's quickly become my favorite garden tool. But there is something in particular that I did not understand about how to use it when I bought it. I see now that the manufacturer's product description includes this information, but I didn't really understand it. Now I do.The manufacturer's description includes the following words: "The 0 to 10 scale of the MM24 indicates a relative "wetter" or "dryer". I missed the meaning of that at first. Once I got the meter I figured it out. The 0 to 10 moisture scale is not in some type of universal moisture units. It is a relative scale - relative to some sample soil that you have chosen to calibrate the meter to. The calibration process is easy, it doesn't take more than 2-3 minutes to do. But it is very important.There is a little screw, under a little rubber cap, on the back of the meter. This is the calibration screw. You find (or mix together) some reference sample soil that you feel has a reasonable amount of moisture contained in it for the type of plants you will be using the meter on - not sloppy wet, but not obviously too dry (I used some soil in an outside planter box to calibrate my meter to that I had just watered well and allowed to drain well). With the meter placed at least a few inches into the sample soil, you turn the screw until the meter needle reads "5" on the "0" to "10" scale. Replace the rubber cap over the screw. Your meter is now calibrated to your sample soil. These calibration instructions are actually printed in very small text on the back of the meter.When you test other soils in the future any reading under "5" is dryer than your sample was, and any reading over "5" is wetter than the sample soil was. I have concluded that any reading of between about 3 and 7 are acceptable for the plant I am checking.I think this is a brilliant system. You determine the range of wetness you want for your trees/shrubs/plants. After calibrating the meter to that reference point you are then comparing all other soils to it. If you have dramatically different types of plants (e.g. cactus vs bamboo) you might have to re-calibrate for each of those.My meter is the 24" version. When checking trees, especially two young small ones I have planted during the past few months, I have found it is important to slowly push the meter stem all the way down the 24" inches, while watching the meter during the process to get an idea of how wet the soil is at different depths. Sometimes it is pretty dry the first few inches, but by the time I get about 12" to 15" deep it is registering 8 to 10 on the meter. So I know not to water yet because the tree's root ball was planted 24" deep. Other times it is pretty wet the first few inches from lawn watering, but only registering 2 or 3 on the scale at deeper levels, so I know it is time to water it.