Hi,
Suggest you consider using walls of water (WOW)(Season Extenders) to start your plants a few weeks early next year. You will not need to fiddle with them daily like a cold frame.
I built coldframes to fit in my raised beds, but designed them mostly for late winter greens. They are wood framed foam board with double vinyl tops and automatic lid openers and solar powered ventilation. (kinda geeky). You put a blanket on top when it is too cold, a light bulb inside when it is really cold and a sunscreen on top when it is too hot and sunny. Too much work.
I did not use them at all this past year. Just took the plants directly from the 4 inch pots (after hardening) to the raised beds with WOWs. Ground temperature is as important as sunlight in the early season. WOW will warm the nearby soil without all the fuss and tending of a coldframe and my tomatoes outgrow them in 2-3 weeks. Some use a ring of full 2 liter bottles painted black but WOWs perform better for me.
For the raised bed in your picture, you could also try a small hoop house over the bed using PVC pipe or metal conduit for the frame and sheet plastic for the covering. It would need to be opened every morning and closed every evening, without fail, or you could lose everything.
Again, you are only talking about a few weeks in the spring when this will make a difference.
Hope this helps,
Rick
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