I wouldn't grow anything along with a montana type - they get 30 feet eventually and take up a lot of room, anything else growing with it will be drowned out.

If you are growing two or more clematis together, you also need to consider when each of them needs pruning. They will cling to each other so, if they need pruning at different times, separating them is going to be tricky

I had considered all the points you both raise, but thought it worth asking the question. I will rethink were to put them - cheers

Neither Clematis montana nor C. cirrhosa require pruning, but their growth rates are so dramatically different that, as Bamboo says, the montana will simply smother your two cirrhosas as well as taking most of their light, water and nutrients.

You could potentially try the same idea but with C. armandii & C. montana - I've seen them successfully grown side by side, at least....it's a clash of the Titans!

I have 3 types growing over my walls Tilley...the Montana from next door, which over the years has grown along the top and down the sides.....clematis cirrhosa Wisley cream coming into flower in November, a little lower down and now Alpina Willy is full of bright pink buds. The four years we have been here, I have trimmed all 3 where I could reach and this last winter has checked the montana, though the alpina is healthier than ever, with lots of new ground growth I'm hoping to grow as new plants.....:o)

thanks everyone. think i will have to resort to finding another space for them - not sure where though, already have too many climbers lol!