Controling tempature and rainfall in the potato bed

I have started this garden bed 1 month early. See the post below for more info.

On March 16, 2015. Temperatures stared to drop into the high 30's F
So, I went ran outside and added a plastic cover to the top of the bed. This allowed me to control the soil temp decrease. It only went down to 48f . The next day I did this video. (March 17)

The next day. March 18,  I took the cover off again for  few hours. Air temperature was 44° | 37° ground temp 48. It went back up to 50f. 

March 19, air temps 42° | 35° soil temps 49-50 rain fall .11 inch 

Today March 20.  air temps 55° | 43° Soil temps 50- will put in the number when I cover the bed for the night. 
Note. This bed contains potatoes I started from Pull sprouts.