The new ML3 ThetaProbe has extra features, improved performance and a new look. With its 1% accuracy the ThetaProbe continues to set the standard for soil moisture measurement but now also measures soil temperature.

With the ML3 ThetaProbe Soil Moisture Sensor it's easy to make reliable, accurate soil moisture measurements. Simply insert the soil moisture probe into the soil, connect to your data logger or readout unit, provide 5-15V DC at 20mA, and within seconds you can be logging soil moisture.

The ML3 ThetaProbe is robust, buriable and maintenance free (environmentally protected to IP68) . It can be easily installed at depth into augered holes using the optional extension tubes.

What's New?
Since the ThetaProbe was introduced 18 years ago it has seen many improvements. The new ML3 is the latest step in that evolution. The addition of a thermistor sensor enables the simultaneous logging of soil temperature with soil moisture. A new cabling system makes it simple to extend or replace cables. With a choice of 1m, 5m, 10m and 25m extensions, flexible configurations are now possible. ML3 cables and connectors are buriable (environmentally protected to IP68).

The ML3’s salinity response has been improved - its output has been characterised at EC values up to 2000 mS.m-1. The temperature range has also been improved with tests demonstrating that the ML3 can operate at temperatures as low as -40 degrees C.*

* Non-flexing cables

The ML3 ThetaKit
This portable kit contains all the items needed to make rapid spot readings of soil moisture content with a ThetaProbe. The ThetaKit includes an HH2 Soil Moisture Meter readout unit, spare ThetaProbe rods, insertion kit and carrying case. 

Note: The HH2 Meter does not provide temperature readout or recording.


  • Class leading ± 1% soil moisture accuracy
  • New built-in temperature measurement (only when buried)
  • New extendable cable system
  • Easy data logger connection (0 – 1V DC)
  • Improved calibration for soil salinity
Output 0 to 1.0 V differential
Power 5 to 14 V, 18 mA for 1 s
Sample vol. ~Approximately 60 x 30mm diameter
Size 6.7" x 1.5" (170 x 40 mm diameter)
Environmental IP68, -40 to +70° C
Water Content Accuracy ±0.01 m3.m -3
Range 0 to 0.5 m3.m-3
Salinity Range < 0.035 m3.m -3
50 to 500 mS.m-1
Temperature Accuracy ± 0.5° C, 0 to +40° C
± 0.75° C, -20 to +60° C [1]

[1] Figures apply to sensor only and exclude logger or cabling errors