We have a solar growhole with raised beds. I notice the soil temperatures really follow the air temperatures. If there's nothing else in your hoop house I guess you could allow it to overheat for a few days, see what that does...
Our growhole is small 8' X 16', looks to me like the only way to grow stuff through the winter is to add some bottom heat.
One fellow detailed a method where you'd bury 4" plastic pipes in the beds, then use fans to circulate excess heat through there. That will only work IF you have the sunlight to generate the excess heat......
Pull back any mulch to expose black dirt. Light colored mulch really keeps the solarenergy out of the dirt (good in the heat, not in the spring).
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