tob2 ; I don't know what climate zone you are in, nor your geographic location, anyways ,.. here goes ..
The DIFFERENCE BETWEEN A "COLD FRAME" versus a "HOT FRAME"
A Cold Frame is a surface mounted box, basicly aimed to the south to collect maximum sunlight, and covered with Glass, or a translucent material to increase sunlight and warmth.
A Cold frame will extend your growing season by 30 - 40 days, and uses the sun as a heat source.
A HOT FRAME is generally a sunken insulated mounted box, aimed to the South for maximum sunlight,covered with glass,
whereby heat is generated by "HOT MANURE" and sunlight.
HOT MANURE is FRESH HORSE , or FRESH CHICKEN MANURE which is high in Nitrogen, and gives off heat as it oxydizes and breaks down(like compost); cow manure is not hot (nitrogen) enough.
Due to cold snaps, frequently it requires a blanket/ comforter placed over the glass on cold nights to keep the warmth inside (ie: additional insulation).
With the HOT FRAME you can extend your growing season by 40-80 days, depending on nightime temperatures,insultion, and willingness to put the extra effort of blankets at night.
This is how the early colonialists extended their growing season, as at that time horses were used as draft annimals and for personal transportation.
The invention of the gasoline /diesel tractor, and the automobile, has eliminated the need for horses, and much of history has already been forgotten .
Hmmm, now I’m thinking of starting that corn a couple weeks earlier than I’d planned. I have a ‘honey do’ project now.
Thanks for the information. I already knew about cold frames having used them in the past when living up north. Did not know about, because of having never heard of them, the hot frame. At any rate, I will do what I can to let the eggplants mature. Living in an apartment complex and being allowed to have gardening pots only is limiting but I am grateful the landlord even lets me have them! I’m amazed at how much can be grown in them and with mostly bright indirect light.