You may recall from a previous post that we have installed a hoop house/cold frame in The Learning Garden. As part of this project we are following the air and soil temperatures. Those temperatures are summarized in the graph below. We compare the soil temperature inside the hoop house (orange) to a similar bed without a hoop house (green). The hoop house does consistently increase the soil temperature by about 5 degrees. The fluctuations are largely due to the amount of sunlight on the particular day that the readings were taken. The high temperatures during the day are also dependent on the amount of sunlight. On bright sunny days the high temperatures approach 80 degrees. Venting keeps the heat from building up to excessive levels. The low air temperatures probably are similar to the outside air temperature. The hoop house if just too small to hold heat through the night. On April 7 radish and lettuce seeds had germinated.
The other temperature study that is going on is black vs clear plastic mulch laid directly on the ground. It is very clear that clear plastic, the green line, heats the soil faster. The temperature difference is 10 degrees. The soil temperature is similar to the hoop house temperature. It was a bit of a surprise that black plastic did not affect soil temperature compared to no covering. Although the sun does heat the plastic, that heat is not transferred to the soil. We will be continuing this study through the summer.
Written by Tom Wentzel
Posted by Rachel