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Germination Thermostat


Our Germination Thermostat allows you to set and maintain a specific soil temp in seedling germination trays. Compatible with all Hoss Germination Mats. 32F to 140F temperature range with Celsius or Fahrenheit display. Temperature probe and 6′ power cord included.


The Hoss Germination Thermostat allows growers to select and maintain optimal rooting temperatures when germinating Seeds or rooting cuttings for fastest growth. This will ensure that optimal germination conditions are present so that maximum germination rates may be obtained. This thermostat is compatible with all Hoss Germination Mats (17 Watt, 100 Watt, and 150 Watt) and most other seedling heat mats.

It includes a temperature display range from 32F to 140F with your choice of a Celsius or Fahrenheit display. Operation is easy with a simple, push button display for changing the temperature settings. Each unit includes a temperature probe and a 6' power cord.

The controller is designed to be able to reach the set temperature within five hours. If the controller is powering the mat constantly for longer than five hours, it indicates that the desired temperature is not being reached and that the surface where the mat is situated may not be insulated enough.

To remedy this and increase the mat’s effectiveness, relocate the mat to a more insulated spot or place insulative material underneath the mat. Surfaces made of concrete, cement, or steel are unsuitable as they absorb too much of the mat’s heat. The use of a humidity dome is strongly recommended, as this helps with heat retention.

If the probe senses a temperature of 108°F, the controller will shut down via the automatic safety shutoff. A suction cup for the probe is included in case you would like to use the controller to control air temperature. This is done by clipping the suction cup over the probe and then affixing the suction cup to the inside wall of the dome (wetting the suction cup is helpful).

Germination Thermostat Instructions:


  • Insert the temperature probe about 1" to 1.5" into the root zone, preferably into a media pellet dedicated to this purpose.
  • Place the controller somewhere up and away from the tray and any stray water. DO NOT SUBMERGE THE CONTROLLER OR ALLOW IT TO COME INTO CONTACT WITH WATER. Avoid immersing the probe in water as well.
  • Plug the heat mat into the power receptacle on the controller.
  • Plug the controller’s power cord into a 120V power outlet. The POWER LED should light up.
  • Set the maximum temperature you desire for germination or rooting. Most gardeners find that the optimal range for this is between 68-72°F


  • Press the SET button. The numeric LED display will show the unit’s current temperature setting (preset). By default, the controller's LED display will always show the temperature being currently read by the probe until SET is pressed.
  • Press and hold the SET button until the LED display flashes. Now you can adjust to your desired temperature setting by pressing the UP and DOWN buttons. Once you get to your desired temperature, press SET again. This will confirm the setting.
  • Note that the controller will cycle power on and off to the heat mat according to temperature information it is getting from the probe. This is normal, and you will see the HEATING LED light up and turn off intermittently. When the HEATING LED is lit, this means the controller is giving power to the mat and it is heating. When the HEATING LED is not lit, the mat will not be providing any heat at those moments.
  • To switch to Celsius display, press and hold the DOWN button continuously for three seconds. To go back to Fahrenheit display, press and hold the UP arrow for three seconds.

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