The cole crops seed germinate when SOIL temperature reaches 55F So if want a early start germinate inside & let them develope in side & set out later......Tomatoes seed germinates at 70F & the plants DO NOT like the COLD> Start inside & set out after night temp is above 60F..The squash & mellon prefer direct sowing after last frost date..

As a general rule cold frames are much more difficult to monitor and regulate than starting things inside. Thus more risky. And in your zone, unlike further south, balancing the temps inside it can be a real challenge.

So the more time you have to monitor and adjust it - such as home all day so can check it hourly vs. work all day - or the more you can automate it with things like soil heating cables and auto vent openers the better.

This is not to say it can't be done or that it doesn't have advantages - it can and it definitely does. But experience with working with one is a BIG part of success with it and inexperience can mean whole crop loss.

Dave

This page explains the advantages and disadvantages for starting tomato seeds in a greenhouse, using a cold frame, starting them under lights, and using a sunny window. Basically for tomato seeds, the idea is to have consistent temperatures at 70 degrees and give them 12-18 hours of light per day.

Here is a link that might be useful: What tomato seedlings need to grow

The lettuces, spinach, kale and cabbage would be fine out in a coldframe. I've been growing all 4 of those all winter long. The spinach has been doing quite nice.

The warm season stuff cucumbers, tomato, squash and melons are okay in the coldframe but not until 2-4 weeks before your last frost date. If you put them out earlier than that they may get too cold at night and become stunted. Unless maybe you want to have a heated coldframe which is them called a hotbed. I use Christmas lights for extra heat. I thought about the buried cable option but I have a way of accidentally digging up things that are buried.

As digdirt said coldframes/hotbeds are something that one needs to monitor every day. I use 4 different methods. The frames wide open for days above 40F, cracked open about 3 inched for days 30 to 40, cracked open 1/2 inch for days 25 to 30F and closed fully below 25F.

Just harvested a bunch from this frame. :-)

{{gwi:222393}}

Last month I germinated lettuce, spring onions and radishes indoors, then hardened them off and put them in a small greenhouse I purchased from amazon. It is only about 6' tall and 2' wide and fits nicely into a corner of our deck. I think it is functioning similarly to a cold frame. Like others have mentioned, the only drawback I've found is needing to monitor the internal temperature of the greenhouse. Once external temps get to about 60 outside, it is blazing hot inside and I have to remember to open it up. Other than that, it's working well for me. I'm planning to move pansy seedlings out to it soon. I am waiting to start tomatoes and peppers indoors closer to our last frost date though.

gjcore - that frame looks awesome! What is your protocol for turning on the lights? And I assume that your temps for opening etc. are for daytime highs?