Hello, love your post, and cold frame. Thanks for posting.
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I live in zone 6b, I hybridize daylilies for a hobby. I also use a cold frame a lot like yours. Will try to post some pictures.
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My cold frame is constructed of, wood frame, single wall polycarbonate panels all the way around the frame and lid. For ventilation I have a house foundation vent ( 8 × 16 ) that is heat activated ( totally open at 70 degrees, closed at 40. ).
In our coldest months ( Jan. Feb. ) I staple large bubble, bubble wrap to the inside frame,for added protection. Have thought about the light bulb, but have not tried it yet.
Daylily seeds are started in sept., planted out in seedling beds in May.
Like a lot of your ideas,will be trying some
although daylilies are different a cold frame works great for a lot of plants. Thanks again for your post.