I guess it all depends on what and when you want to grow. With out heat you would be hard pressed to use your greenhouse for frost sensitive plants before mid-April.

What type of greenhouse are you looking at? What type of glazing? Any plans for insulation?

I have a polycarbonate glazed greenhouse and with subfloor insulation and bubble wrap wall/roof insulation it can hold the tempsabout 10 degrees above outside temps. I use my greenhouse for seed starting too. I heat mine so I can start using it in late February. I am in Western Massachusetts in new USDA zone 6. Our frost free date is generally May 25th or so.

hello Tim,

i live in zone 4 and that is between a rock and a hard place.

the rock is if you don't start your plants early and get them quite large to transplant after the last frost you won't get a very big harvest.

the hard place is it is very expensive to heat the green house.

we have a very good but standatd greenhouse.

we have propagation heating pads with thermostats, however that is not enough to protect our seedlings as early as we have to start them.

so we built foam boxes with a easy to remove lid and put our propagation trays in them

next we build mini greenhouses over our grow boxes in the greenhouse. this is where we put our seedlings after we trans plant them. this will protect the cole plants down to about 12 degrees. the tomatoes and ect. to 18 degrees and the cucumbers and ect. to about 25 degrees.

we start our cabbage and frost hardy plants the 1st of Feb. our tomatoes, peppers, egg plants and corn (yes we start our corn in the green house) on the 1st of March. and we start our cucumbers and melons and such on the 1st of April.

when your season is short you do things to make up the difference.

there is a way to heat your seed house but there is more capital out lay. if you are interested send me an e-mail. my e-mail address in on my page.

Dean

How do you contol the heat of your propagation boxes so as to not over heating? Do you place them in the foam at night? Got pics?

So really a small cold frame would work for short plants anyway.