First robins of spring

We had our first spring robins in the yard yesterday - a hopeful sign, even if most of the yard is still snow-covered. The greenhouse has made it through a fairly typical Michigan winter using only 60% of the propane tank filled in November. This is tremendous progress from the first couple of years; I may have finally hit on the right balance of heat sinks and other heat-retaining methods for a hoop-house this size in our climate. It's still surprising to me that I've not been able to locate more published information on home-greenhouse maintenance for this climate, but through various readings from writers and bloggers in other zones, I seem to be finally piecing together what works here.

The next challenge, coming up quickly now, is how best to circulate the air and cool the greenhouse as the days become warmer and sunny days begin to be predominant, overheating the greenhouse by 1pm. So far just opening the glass of the screen door part-way has been sufficient to prevent overheating, but soon it will require more than that, complicated by my being gone during the day and unable to fine-tune adjustments as the day progresses. I'm looking at several alternatives now to provide better air circulation and cooling of the greenhouse for the spring months, and will report them here as I try them.