For sowing seeds and transplanting seedlings, you might think that the air temperature is important. If you really want to get the most out of your garden, then you should focus on the soil temperature. The best way to measure the temperature is to use a soil thermometer. I’ve been using the AcuRite 7 inch Soil Thermometer. There is also one that is 5 inches long and there are digital soil thermometers.
This thermometer goes from 0 to 220ºF. While they say that most plants will germinate best between 65 and 75ºF, there are exceptions like cool season veggies that can germinate down to 45ºF. Also, some warm season veggies can germinate up to 90ºF.
You can use this thermometer inside or outside. I use it more outside.
If you are measuring the soil temperature for sowing seeds, then you should measure about 2 inches below the surface. If you are transplanting, then you should measure the temperature between 4 and 6 inches below the surface.
