this has nothing to do with your winter sowing.. just forget about that.. with this ... odnt complicate it all trying to compare such ....

are they fully dormant or active??

if dormant.. just put the pot in the garage or shed... and let them stay dormant.. easy peasy ...

if they are active... tell us.. show us ... and we can go from there ...

i would not force them into early growth ... and in my z5MI ... they wouldnt be actively growing for at least another month ... and you are going to have all kinds of slow motion hardening off to deal with.. if you get them too far along too early ...

ken

I've had decent luck with those bagged clematis potting them up and growing them in a south window in the house until they can be hardened off and planted outside. It's not ideal, but since it sounds like they are growing already, its better than keeping them in the dark. I don't buy them in bags anymore, since overall, It seems they take much longer to get established than getting them already potted (even in tiny 2.5 inch pots). Yours will probably be fine potted up until they are ready for outdoors.

Sam's advice is good. I've grown scores of clematis over the years, including boxed or bagged clem roots that are available almost everywhere in early spring. In fact, some of my most desirable and difficult to find clems have been obtained this way!

IME, these little starts are too small and too vulnerable to be planted out directly and should be grown on in pots until they are of adequate size and root development. If I do purchase clems in this manner I will grow them on until the root system fills a nursery 1G pot. And then plant them into the ground in fall or hold over until the next spring if not quite to that stage. And I do the same with any small potted clems - the 2.5 or 4" pots.

In my climate, cold is not a concern with these potted up starts so they are outside from the start.....but just not in the ground :-) In climates that still have the potential for some cold weather, I would wait until temps are consistently above freezing at night, then gradually acclimate them to outdoor conditions. The roots in pots will be fine........it is the tender top growth that could be damaged and that is what needs to be hardened off.

And if they have top growth already - which it sounds like they do - light is essential!! Continuing to keep them in the dark will result in anemic, weak growth that will put your new vines off to a poor start.

Yes, agree -- pot them up and set them in the window for now. They'll be fine.

ETA: You can also set them outside during the day and bring them inside overnight if weather permits -- they'll get better sun exposure that way.

Just to say, I bought a boxed Clematis over a decade ago and it's been a great Clematis all these years, good luck with yours!

Give them shade when you start putting them out. Since they started trying to grow (“ one long pale tendril of a stem coming out of each root ball”) they need light, but will sunburn if they get full outdoor sun before they have had a chance to slowly get accustomed to it. To give them bright outdoor light but not full sun, I often put plants out during the day on the north side of a structure if it above freezing, and bring them in at night. Warmer nighttime temperatures than daytime on young plants has been shown to encourage stocky, stronger stems.