Brigadoon - An Occasional Corner on the Internet
Ground Temp Sensor Depth Selection
Designed by Mark Little
The general standard for meteorological ground thermometers is to have a sensor at 10cm, 20cm, 50cm and 100cm. Since a suburban block is unlikely to have the environment to strictly meet the environmental standards for ground temperatures, it is better to determine what sensor configuration would be (1) provides information relevant to the backyard environment; and (2) is relatively easy to install.
For a home garden, the temperature in the 10~20cm range is what is relevant for the germination of seeds in the garden. Thus, those depths meet the first requirement of providing relevant data. The deeper levels (50cm and 100cm) are less relevant to determining planting cycles, but since sensors are being installed, it is a question of how easy it is to install the sensors to give readings of interest (rather than immediate practical use).
Previous experience with installing ground thermometer sensors in the local backyard indicates that it is fairly easy to get a sensor down to a depth of 50cm, but it can be much harder to get down to 100cm. In the end it comes down to whether the difference in effort getting sensor in 50cm or 100cm is worth it to you.