There are a lot of people who do not heat their greenhouses in the winter. I have discussed the options in this blog post. https://www.blog.advancegreenhouses.com/the-winter-greenhouse-heat-or-not-to-heat/ One of the options is to "dress in layers" just like Mom taught us. The cold frames are a great idea, but you will need to monitor them at first to see just how the temperature is reading. I would get a max/ min thermometer and put it in the cold frame. That will help you to get a clear picture of what is going on in a hurry. Tammy

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.

Scott, Without a heat source a greenhouse or a cold frame will be the same temperature as outside once the sun goes down. They will not maintain any of the heat they have built up during the day. That being said, there are a couple of options. You can use a heat lamp inside the cold frame. Just be sure that it has plenty of clearance on all sides and watch it if you are doing any watering. Another option is to use heat cables. We have used these in our cold frames and grown all winter long. Of course I am in zone 8, but you say you are only looking for some extra time in the fall. We attach these to the bottom side of a piece of hardware cloth with cable ties. We then place 4 or 5 inches of dirt over them. Of course we are not in pots, we are growing directly in the soil. You can also supply some insulation from the outside of the cold frames. You can take a used burlap sack or even a pillowcase and fill it with some type of insulator, such as leaves. Just place these over the top of your cold frame at night and they will help increase the temperature slightly. Hope this helps. Tammy

Yes, pure compost is rarely recommended for planting seeds or even starter plants and for more reasons than just the weed potential. You really want a mineral based soil....like garden soil (with some organic amendments) or an appropriate bagged raised bed soil.