greenhouse stayed warm this morning

greenhouse stayed warm this morning, I have a small GAT system circulating air through the ground, it was 2C at 8am and the greenhouse stayed at 8C. which is good because all tomatoes are in there.. heating a greenhouse without an actual heater is tricky, and even though I built it into a hillside and lined it with water barrels, until I started circulating ground heat with a blower the inside temp would quickly drop and could freeze during a light frost at night. These wireless thermometers are super nice to monitor. #greenhouse #greenhousegardening