Hi, I bought two young clematis (Warsaw Nike) at a garden centre the other day. They are both flourishing, but are only about 15 inches tall on a single stem, so very immature. I have a conservatory which gets very hot in the day, even with only winter sunshine, and it's freezing at night, so no greenhouse. Should I cut these two back and leave them outside to their own devices? I don't even have a sunny windowsill, as the front of my house faces north. I would really like to bring these on. How can I do this please?
Caro
I can't think of any reason to keep them indoors. Do you intend to grow them in soil in the garden or in containers? If in soil I would plant them out now with the top of the root ball about 2-3 inches below the surface. Prune them back to a set of buds in late winter or early spring They should be pruned to about 6-12 inches and feed after pruning - potassium rich fertiliser is best. This should encourage them to produce new shoots and give you a bushy plant.
If in containers you probably need to put them in relatively deep containers (mine are at least 15 inches deep - maybe more). Plant in good quality potting compost Prune etc as above.
If you can't plant them out yet, or are unsure how hard your winter will be, try potting them into wider, deeper pots in good compost with a bit of extra bonemeal for root growth. This will help insulate the roots over winter. Keep them in the conservatory till they've put on some top growth next spring then plant them out at least 4" deeper than they were in the pot as this will encourage more shoots to form.
I have kept young clematis over winter in my unheated greenhouse this way and it has worked well.