I built my own cold frame, but it doesn't work because I go to work early and I can't stay home to adjust the lid during the day. You want an auto vent opener. I have a Bayliss MK7 and I like it a lot. Dan

I currently have tomatoes and peppers in a cold frame. The seeds started indoors, and they moved out after about a week of development. They did not yet have their first set of true leaves when I did this. The ambient outdoor temp is around 45-60 degrees during the day. On sunny days with a higher temp, I open the cold frame up and let them soak in the sun...on colder days I keep the lids (old storm windows) down all the way. On moderate days or cloudy days, I open the windows just a crack (about 2 inches). My plants have been spending the days outside, and the nights in my laundry room, roughly 55-60 degrees at night, as nighttime temps have been dropping into the 30's still, and a few nights in the mid-20s. My plants are short and stocky, having been exposed to such cool temps, their growth rate is slow. They all have their first set of leaves, but none have a second yet. In the next few days the overnight low is not expected to be below 40, so they will spend the night outdoors for the next week, but still inside the cold frame. Cold frame philosophy, daytime temps are warm enough to keep the plants happy with the sunlight. Nighttime temps can fall to just a few degrees above the outside ambient temp. Unless you do a great job of insulating the frame, you will lose a lot of heat gained during the day, and you won't want to keep your plants outside at night. This in and out can get tedious, but if you love your plants, it's worth it! Cold frame construction: I used a wood pallet as the base, and a deconstructed wood pallet for scrap wood for the sides. The top (about a 30 degree angle downward) is two old storm windows. You can use just about any clear material as the top. Make sure that you can open it up though, as it can bake the plants on a sunny day!

I would build a cold frame, with a sloped drainage pan so the water drains off your deck. I would also buy a couple of heater cables and bury them in the soil. I would also put some type of insulation around the coldframe. This should keep the soil warm, and the inside temp of the cold frame well above freezing. You will have to watch very closely for disease. Mother nature isn't easily fooled.

The main problem with sensative crops like tomatoes is that you will need to constantly monitor temperatures in a smaller enclosure. One month gain in starting is a more realistic under most conditions and then you would be best to germinate tomato seeds indoors at much higher (80-85F) temperatures before placing seedlings in the frame. A few thimgs that are useful for a smaller unit: For an aid with heat a light bulb or string of Christmas lights may make a big difference on cooler nights. For daytime a hinged cover that can be propped at various heights is helpful. If you have an old waterbed or swimming pool bladder you can lay it inside and partially fill it to buffer the heat extremes. A thermometer laid inside will be helpful during your frequent evening and early morning visits when you have the unit tightly closed. Cold Frames tend to work best for hardier crops like cole crops or onions. But if that is what you have available you can easily make it work for almost any crop. Years ago they were the plant starting structure of choice for most home gardeners.