When I first set out to learn to grow flowers, the process of overwintering hardy annuals was one which seemed totally foreign. With very little information on the process online, most of what I’ve learned about crop protection has been through the process of trial and error. In general, crop protection will vary from one flower type to another. However, for this post (and in my backyard), I usually just apply the same “rules” to everything that I grow. It makes things a lot easier.
Here’s a look inside the hoop house when it is on “lockdown”. Basically, this occurs where the forecast is especially cold. Here in my zone 6b/7 garden, we get a moderate amount of snow and cold temperatures. Though we don’t usually get more than six inches of snow at once, the temperatures can dip down into negative single digits (Fahrenheit) on occasion. During the coldest months, temperatures in the teens are very likely. 
Any time night time temperatures drop below 30F, the plants are covered with row covers and the hoop house is closed. This is especially true when the extended forecast shows no signs of warming up. The row covers will also remain in place during the day if there’s no sunshine. If the sun is shining, it’s likely that the inside of the hoop house is much warmer than the outside air. In these cases, I’ll go into the hoop house and remove the row covers while the temperatures inside are warm. 
When night time temperatures are above 30F, I don’t cover the plants. Since the plants are hardy annuals, they are able to handle some cold and an occasional frost that may occur in the hoop house. Since my tunnel is not ventilated, it can get very wet and humid inside. It’s not ideal, but it’s just something I deal with in my backyard.
If day time temperatures are above 30F, it is very likely that (in addition to removing row covers), the hoop house will need to be vented. On sunny days, the temperature can easily climb to an uncomfortable heat that is not conducive to plant growth. Sometimes, I even have to remove the entire end piece of plastic to remove excess heat and humidity. Properly managing an unheated hoop house is all about regulating temperature as best as possible.
Making decisions regarding when to open and close the hoop house will definitely vary from one garden to another. Every climate is different. I hope that this post was helpful. Thanks for reading!
