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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.
I try to use my soil thermometer every month to take readings. It's important to realize that your soil is going to be different temperatures at different depths so you have to take it at the same depth each time.
Another good tip is that you might have micro climates on your property and this is a good way of finding them. These are areas that are generally warmer or cooler than the surrounding land.
If you do have a small patch of warmer or cooler soil, you can have a wider range of plants which is always nice. This is where, for example, you can plant some succulents in a temperate zone, or some apples in the semi-tropics.
Your soil temperature thermometer is the best way to find these little spots.
If you want to make compost, you need to have a proper outdoor thermometer capable of determining the temperature of your compost as well as your soil.
A lot of compost heaps fail because people don't pay enough attention to the temperature. If you let it get too hot it can kill off beneficial bugs and bacteria.
If it gets too cold on the other hand, it won't rot down very quickly. A thermometer can help you to determine whether you need to turn it, or add some water to help heat it up again.