The above graph depicts temperatures over approximately 30 hours inside our home (the lower level), outside, and inside the cold frame we built during the series of Community Partners in Gardening workshops. As the graph begins, the cold frame – outside temperature difference was minimal because we had just set up the 6 gallon water thermal storage. Note the quick climb of temperature Tuesday morning as the sun began to heat things up. Around noon, the cold frame interior temperature reached about 97 degrees while it was about 50 degrees outside the cold frame.
During the time period from late afternoon to Wednesday morning, the cold frame temperature tracked the outside temperature fairly closely with the exception that it was about 10 degrees higher. About 7:00 am the outside temperature registered a “plant killing” temperature of 22 degrees while the cold frame temperature registered a “plant survival” temperature of 32 degrees.
The cold frame would have protected plants through the night. Adding more water would increase the heat storage and thereby increase the nighttime temperature during the night.
On the other hand, the spike in temperature midday is cause for concern. We’ve purchased a Univent which will raise the cold frame lid when the temperature reaches about 80 degrees. Hopefully, the midday temperature will moderate after installation.