It depends on how low the temps in there are. Do you have a thermometer in there now, so you know? Lettuce, spinach and cool-weather crops may be just fine. Tomatoes, peppers, squash, etc, may require a heat lamp over them at night. Sue

Thanks to everyone for your good advice! I am planning to set up my greenhouse tomorrow (after the big thunderstorms come through tonight!). I decided to put it down in the yard, against one wall of the house, facing south and east. It is so windy around here - we frequently have furniture blow off the porch - that I would feel better with it staked securely (which I can't really do on the deck). I have a portable electric heater which I will be using at night, the kind that shuts off if it tips over. I think I will also put in some Christmas lights for a little added heat, and so I can see if I go out there at night, and because I haven't put them back in the attic yet - LOL! I plan to set it up and then monitor the temperatures for a few nights to see how it does, before I move my babies out there. Oh, and I will be putting my roses that I have purchased but have not planted yet in there as well. They are all piled in the half bath and you can't even get in there! I figured I would move about half my seedlings (that are ready) out at first and see how they do. I will probably ask for volunteers - some of my hollyhocks look pretty brave! I'll let every know how it turns out.

My seedlings are growing slowly in the greenhouse as well, but nighttime temps out there have been pretty cool, even with the heater 40's and 50's. From what I read, I assumed it was better to grow them cooler and slower, so I wasn't worried when my tomato plants took around 3 weeks to get thier first true leaves. Now they're still growing slowly, but they are getting ever bigger, and they've been out there for a month. Some days it gets hot during the day (when the sun's out), but some days it stays in the 60's - 70's out there. Nights are always cool here just yet, though maybe it's warmer where you are. Depending on when you started them, it may just be that they're growing slowly (and will hopefully be stronger plants for it). My flowers and peppers were the same way, very slow growing, but the stems are thick and the root systems are really good, so I'm not too worried about it. Some light fertilizer might help - I feed mine used aquarium water, which seems to make them quite happy... Good luck, hopefully everything will spring up soon!

I suggest you go with a cold frame not a greenhouse. I have the mini greenhouse pictured here as well as my permanent greenhouse. I use the mini one for my greenhouse overflow--I grow a lot of plants. Anyway this pop-up mini can be put up and taken down each year and it stores in it's own case. Mine is 3x8x4 foot tall but you can buy them half the size if that suits you. If you can put grey patio slabs down or gravel for it to sit on the slabs will absorb heat in the day and release it at night. It will give your plants a few degrees of protection but on really cold nights you can add a garden blanket over the mini. I'm not sure but I think they make one to go over the pop-ups. You have to watch the heat build up in them. Because they are low to the ground they heat up fast with the sun but that lowness also helps retain the heat at night. You'll have to open the vents a little or a lot almost every day. Even on a cloudy day it will get too hot in there. http://www.instantgreenhouses.com/