Need some clarification Jackie. Is this a cold frame or a greenhouse? Very different things. I will assume it is a GH since you mention "walking in.

If so then yes it is well past time in your zone to start seeds in a GH. HOWEVER some heat for it may be required on especially cold nights. Right now we are having to heat the GHs an average of 1-2 nights a week and that will continue here until about the 12th of April. And some method of cooling it will be required almost everyday now.

You have discovered one of the advantages/disadvantages of a GH - too hot in the day and too cold at night unless you have an insulated structure and learning how to balance the too is one of the primary challenges of GH growing. ;) The goal is to keep the air temps at plant height between 45 and 70 max. (65 is better)

So assuming you will be starting your seeds in containers and not in the ground as with a cold frame and assuming you will have a source of bottom heat to use for germination (soil temps of 70-85) then get a couple on min/max thermometers for monitoring your air temps and start planting your seeds.

Hope this helps.

Dave

PS: be sure to check out the Greenhouse forum here too.

Hi Jackie:

I assume you mean a greenhouse if you can walk into it and not a cold frame. A cold frame sits low to the ground and you can't walk into it. It would help if I could see a picture of it, but I'll go on the premise that it is actually a greenhouse. I have had a homemade greenhouse for many years and I think I can give you a few tips.

First make it as air tight as you can. Next is there any way you can section off a piece for seed starting. You don't need the whole greenhouse to start seeds and there's not much use heating the whole thing. A floor of stone or cement slabs or a combination of both will also help retain heat in the greenhouse. Often in old greenhouses you will see a brick or stone wall on the north side. That was not just decorative but also a way of heating the greenhouse at night.

There are 2 things I think You should consider buying. One is a minimum-maximum thermometer, and the other is a heater with a thermostat. The minimum-maximum thermometer gives you the lowest and highest temperatures since it was last set. This allows you to set the heater so it stays above freezing and lets you know when it's too hot and has to be opened. I live in zone 3. I open my greenhouse in mid Apirl. Our last freeze date is the end of May, so I would say you are just about right starting now. By the way I figured out it costs me around $50 for the season to heat my greenhouse with an Electric heater.

You have discovered the magic of a greenhouse. Yes it can be below freezing and if the sun is shining it will be too hot in the greenhouse. I try to keep mine in the 70's in the day, but at night it can go down to the low 40's.

If you don't want to heat at night, then have something you can cover your plants with when the thermometer dips very low at night. During greenhouse season I watch what the temperature is going to dip to every night. I do recommend you get the thermometer. It will be a great help with knowing what you have to do.

If you have any more questions post them and I'll be happy to answer if I can