Encouraging flowers

Is there any way I can encourage my clematis montana to flower for a second time this year?

 

Hi Linlin, You could try dead heading once the flowers are going over, it sometimes works on bedding plants and roses, I don't know about clematis.

 

That could be a big job, as they grow up to 30 foot! :D

 

Which brings me to another point......I don't want them to get overly large so is it okay to restrict their growth now? They were planted in March/April, flowered immediately and are now putting out new shoots all over the place.