Heating Cable For Rabbit Watering How Much Soil Heating Cable Needs To Be Ran Through A 35 Gallon Plant Pot?

How much soil heating cable needs to be ran through a 35 gallon plant pot? - heating cable for rabbit watering

I'm warming the earth in a greenhouse is usually around 40 degrees C at the coldest point in the night. Such as heating cables needed to make a pot of 35 gallons per chip heat?