A soil thermometer is a thermometer specifically designed to measure soil temperature. Gardeners find these tools useful for planning plantings and they are also used by climate scientists, farmers, and soil scientists. Soil temperature can provide a great deal of useful information, especially when charted over time.
For gardeners and farmers, soil temperature is key to making planting decisions. Whether planting seeds or seedlings, if the soil is too cold, the plants may die. While people can use guidelines like the date of the most recent frost, the ambient air temperature, and the time of year, soil temperature measurements can be very important for confirming that the soil is ready for the growing season. Likewise, people who monitor climate and soil health use soil thermometers in their work.
Soil thermometers include a long probe that allows people to reach deep into the soil. Some must be pulled out for reading, using a traditional mercury bulb thermometer design. Others have a display on the top of the thermometer that may be digital or analog, allowing people to quickly read the soil temperature.
Typically the probe is coated to help it resist corrosion. It is advisable to periodically wipe down a soil thermometer to remove soil and any salts that may have adhered, to extend the life of the probe. If the probe is used in a wet environment, it should be wiped clean and dry before being put away for storage. Many soil thermometers come with cases or clips that can be used to protect them for storage while they are not in use.
A quick read soil thermometer will take a reading very rapidly and is useful for a quick probe of soil to check on conditions. Other thermometers need to be left in place for a few seconds in order to generate a stable reading. Some are designed specifically to be left in place. In greenhouses and other highly controlled environments, people may leave thermometers in the soil so that they can take regular readings.
One thing to be aware of when purchasing a soil thermometer is that many have limits on the highest temperatures they can read. If people are using a thermometer to manage something like a compost pile, the internal temperatures may get too high for a regular soil thermometer to read. It is advisable to choose a product with a broad range if this is a concern.