What shall I do with my clematis seedlings?

Liriodendron

I have a dozen seedling clematis, grown this spring from an unknown parent plant, possibly montana, though I was hoping they were C.tangutica.  They have got away from me... I repotted them a couple of months ago, but they've taken off.  They blow over in the wind and try to climb neighbouring plants in the cold frame. 

  

Clearly the pots are too small, but is it too late to repot them now?  If so, should I cut them back, and by how much?  They are clearly different in leaf colour, and to some extent in vigour, so I'd like to grow them all on in pots until they flower, before deciding which to keep in the garden.

Thanks in advance...  

Fairygirl

I'd be inclined to do both @Liriodendron. If they're filling the pots, they'll be fine moved on a bit. Have you got any clematis/rose pots? They would be ideal, just to give them the depth. I could have given you some 

They've grown very quickly!

Liriodendron

They have indeed, @Fairygirl...  I've got a few clematis/rose pots, not enough, but they'll do for the biggest ones.  Do you think I should just trim them to the top of the canes, or be  more radical?

BobTheGardener

Not too late - I would repot them now into 2 litre deep 'rose' pots.  It's still warm enough for them to put on new root growth.  I cut my clematis seedlings right back to about 2" in their first spring after overwintering for the first time and many produced the odd flower later the same year, with the rest of them flowering the year after.  The seeds I grew were mainly from viticellas and crispa hybrids (kindly sent to my by a fellow member here.)

Fairygirl

I think you could cut back quite a bit. What would you think @BobTheGardener ?
If you were able to cut them right back in the following spring, I'd reckon it would be fine to take them quite far. To about a foot or so?

The one on the left looks quite montana-like, but I'd agree - the other one looks different. 

BobTheGardener

Cutting back to a foot or so would be a good idea, I reckon.

Richard Hodson

Possibly both are montanas, there are different coloured foliage varieties on the montanas and lots of different flower colours, well done. It would be good to see a flower but if you prune them back now you will be cutting off the flowering wood for next Spring, up to you. But, as you have been advised on here quite rightly, best to pot them on into 2 litre deep pots to let the root systems mature, great thread,

Fairygirl

Good to see you @Richard Hodson
How have things been this year for the nursery? It's been a difficult year for so many people and businesses. 

Liriodendron

Thank you all very much for your advice.  It was my first attempt at growing clematis from seed - those are all from the same plant, so if one is a montana, they all are!  I do have one other growing from seed, which was from 'Guernsey Cream', but of course it may be completely different from its parent... 

I germinated them in plastic bags containing the seeds on pieces of damp kitchen paper, in my dark but warm shed.  C.alpina didn't germinate though, so I've potted a few seeds up and put them outside to see what happens.  

Fairygirl

Very exciting @Liriodendron. It's something I've never done,but I'm now looking at the lovely seed heads on the macropetala I've got, and wondering if it's worth trying!
Not sure it would be the best time though. 
I've got some 'accidental' cuttings, as I was doing a bit of hacking and slashing recently on the Group 2 that it's with. Not sure if they'll work either, but it was worth a go. 
Now that Richard says it - I can see the montana shape of the foliage on the other plant. It looked different higher up, but I think it's the angle. 
I really hope they all take and grow well for you.  

Liriodendron

Thanks @Fairygirl.  I'll take more photos if they flower in the spring...