I want to make a cold frame. It will only be used to start seeds in the spring (I'm not a veggie grower - yet).

Everyone mentions venting. I understand that you have to prop open the lid during the warm days. Is there a specific outdoor temp recommended for zone 5 for opening it?

I was wondering if it would also work to put floor vents/register vents (like you have in your house) that you can open or close, into the sides of the cold frame for cross-venilation? Open them in the day, close them at night?

I work during the day, will not be able to monitor it, and I doubt I can afford an auto vent mechanism.

Thanks in advance!