I don't bother opening up my cups unless the sprouts are hitting the plastic. If it's hot out I have them in shade and may tear the plastic a bit but I really don't worry about hardening off so much. Mostly I just take off any kind of lid as soon as I see true leaves.

Since they have been growing outside all along, they do not need the traditional "hardening off". Just be sure to shade newly planted sprouts from sun as you would any newly transplanted plant.

When to remove the tops? Depends...if the weather is hot enough to worry about them getting fried the tops need to be removed or more holes have to be cut in them to make for more air flow. Otherwise there is no hurry. They can stay in the covered container until you plant them out or until they get large enough that they are outgrowing the container.

Once it looks as if most of the seeds have germinated I remove the tops as soon as possible to make watering easier in the spring. Sometimes I need to replace the tops or cover them with something if there is frost expected.

If you are concerned about the sprouts drying out leave the tops on until they have gotten their true leaves or they are larger.

In your zone you probably will have more issues now with too-hot weather than too-cold. When nights are staying above freezing, I flip the jug lid open but leave attached. Then for frosty nights I can flip it closed again.

If your jugs are in shade you might give than a little more sun after the "roof" is open.

Karen

For me the real joy of wintersowing is not having to harden off. No more hauling the seedlings outside for an hour, then inside, then outside for longer the next day, etc. Invariably I'd forget them one night or day and they'd suffer.

Caryl