Nice work! That looks awesome! It looks as if your cold frame is facing to the east, with the back of it to the west. correct me if I'm wrong. At high noon the cold frame should have 100% direct sunlight inside, over all the plants. Yours looks just like mine, same plastic and all. The back should be on the north, IE, the cold from should slope downwards toward the south. However, there should be plenty of light that gets in the cold frame through the plastic sheeting. I know it doesn't look like it, but the dull light is perfect for brand new seedlings (like a week old, yours look older than a week) At the bottom of your last picture, the lettuce looks like its getting good light through your plastic, is the wooden frame itself shading the other guys in there? and to answer you about hardening off, seedlings only take me at most 3 days to harden off. I leave them outside in the cold for an hour and then bring them in, and the the next night increase the time by a couple hours. By the third night if it isn't too cold (like below 45) I'll leave them out all night. In a cold frame they should be well ready for a night outside in a windless cold frame. The real bad thing about hardening off isn't the green leafy part of the plant getting cold, its the roots, which are susceptible to shock. soil temperatures, even near the top inch stay pretty even keeled, and change gradually. leaving a plastic potter out overnight meant the root system has to go from 60 or 70 degree soil to 40 or 45 degree soil in the space of a few hours.. its a tough trick to turn if they aren't used to it. Lettuce will germinate right down to freezing temperatures, its incredibly cold hardy. while it takes months at 33 degrees to germinate, the plant itself doesn't need to be hardened off, at least not cautiously so. give it a couple hours in the nighttime cold and then they'll be ready to stay outside. I've never lost a lettuce seedling before, and I've forgotten more times than I can count. I did lose a couple tomato starts to shock one year though... Which part of zone 5 do you live in Chele? If I may be so bold as to ask. I'm on the southern edge of 5, almost to zone 6. Sorry for being a chatterbox. Here is a link that might be useful: My blog, if anyones interested

Hi Steve, To address your original questions about soil heat cables.......we live in a very cold climate here in Wyoming at over 6,000' elevation with winter temps as low as -40 degrees F. We have not used soil heat cables in an outside grow box - but did decide to experiment with a grow box inside our unheated GH. We bought the cable length we needed based on the area we wanted to cover - 30" X 96" and according to the spacing the cable manufacturer recommended. We followed instructions and mounted the cable to 1/2" hardware cloth and then mounted the hardware cloth to cattle panel for extra stability and ease of moving/storing. We purchased a thermostat and set the temperature at 55 degrees F and placed the cable buried 4"s in a raised bed within our GH and made a polycarbonate cover to create a box with lids. We tried to grow salad veggies during the winter months - November thru March. The daytime temps in the GH on a sunny day were between 30-70 degrees F even when OS temps were 0 degrees F so I would raise or remove the lid during the day and cover the box at night when OS temps were as low as -30 degrees F and IS GH temps as low as around 0 degrees F. The soil heat cables were usually only running during the night so I did not notice much difference in our electricity bill. The photo below was taken on January 31st. We are in Zone 3 where danger of frost remains through June 1st and there is snow on the ground usually through April but we have had snow and frost in every month of the year during cold spells. I think most would agree the experiment was a success! The cons in my opinion is the cost of the cables, wire and thermostat and the daily covering/uncovering of the lid (although the polycarbonate only needed to be removed on sunny days because of the heat build-up). When I retire I may do this every winter but for now - it is nice to have a winter break from the GH. We also use the Soil Heat Cable as a germination mat on top of the soil in the GH in February - March as an overflow box from our inside grow lights - that works well too. We are building grow boxes this year OS for our squash and other warm weather plants and appreciate your design!

Back to the original question: Back in the 80's when I had my hardy perennial nursery here in what was then zone 4b, I dug the 6" pots and 1 gallon cans right back into the nursery row to winter and had pretty good survival. A lot did depend on how hardy the actual plant species and variety was though. I had more loss when early spring rains failed to arrive on time, what I called spring drought in those days. That is essentially what we now have with a spring wild fire season. Early and careful irrigation is as important as anything else, if the plant stock is hardy in the first place. The second question about cold treatment: I got almost 100% germination on golden delicious apple seeds by layering them between wet paper towels and then sealing them inside a small tupperware type container that got put in the back of the refrigerator and then just waiting them out. I am not so sure you need to get any colder than refrigerator temps to get your cold treatment. Definitely don't for tulips and similar spring flowering bulbs or garlic; prolonged stay in the refrigerator is used by a lot of deep south folks who grow them there where it would otherwise not get cold enough for long enough to stimulate flower production. I sorta doubt you need to put them outside or in really harsh temps to get your proper treatment. From what I have seen of honey locust, you may not have to cold treat them at all in the first place.

Before I had a greenhouse, I used coldframes a lot. Mine were basically concrete blocks, 2 courses high, stacked on concrete slabs which I laid on sand. I divided the space up into 3 bays, each one about 1.2m square. I used a variety of 'lights' - mostly a couple of old windows with timber frames, plus some polycarbonate sheet. The whole thing was a bit sketchy but I used it for around 5 years or so, raising a load of seedlings and cuttings. Mostly, it kept the birds off the pots and provided a dry space for seedlings (which I sowed direct into 4inch square pots. The back walls were a course higher so that the lights were laid on top at an angle (for water drainage and extra light. It makes a difference how you orient the frames - mine ran across the site, north to south, so the sun hit the surface of the frames all day. It was waterproof but still open to mice so I did protect my sweet peas (for example) with mesh netting or even covered seed trays. Cold frames have a long history of effective use. Although mine has since been filled with soil and is used as a nursery bed, it was a really useful solution to protecting young plants over winter. I have seen little wooden coldframes with polycarbonate lids for sale on the interweb but honestly, this is one of those projects which is easy to build from scrap materials. I guarantee you will be able to knock up a robust and generous frame for a fraction of the cost of buying some shoddy effort off Amazon. My allotment site is littered with cheap garden kit, ranging from plastic cloches, rubbish -plant supports, flimsy edging, plastic raised beds and so on. Nearly all of it will fall apart during its first season.