It's probably out of nutrients and needs a good heavy pruning in early spring every year. I don't know if you have a heavy prune type-group 3 clematis (since no name), but I would treat it as such and see if it blooms next year for you. If blooms are sparce and late, then it's likely a group 2, light or no prune type, thus you only need to remove dead wood after leaf out is complete. Proper pruning and fertilizing are the 2 most important steps for raising very happy clematis.
Fertilize in early spring every year with a good rose food and a few shovelfuls of manure.
There are also the group 1 prune types which bloom in early spring, but I am assuming you don't have this type. They're another story...without pictures it's almost impossible to know, but,... I'm banking on yours being a common group 2 or 3 type.
Suzy

Please excuse the above message as it was intended for a different thread. All of my posts have had major 'glitches' and bugs tonight. This post of mine was typed onto a different thread and should not have ended up here.
Thanks,
Suzy

Like all evergreen plants, old leaves brown and die off on C. armandii. Typically, a healthy plant will just produce new growth that obscures older foliage so it is not so obvious. This can be a very long-lived clematis, so I am not sure why yours is acting so poorly. FWIW, it CAN be cut back quite hard, although doing so now will reduce (if not eliminate) spring flowering - sometimes that is not a bad method to rejuvenate an overgrown armandii. Mulch this fall with a good quality compost and pay attention to late season watering in our typically dry September and October. Give it some rose fertilizer in early spring when you see new growth forming.

Good luck!

I have one 20 feet up my cherry tree so the foliage is not visable in the summer. Another one is covering a arbor of about 10x15 feet. It gets 2 feet thick in about 5 years and I cut it back to where it starts across the arbor. If done right after flowering I do not lose next years bloom. Al

HI, I'm new. I'm also new at planting. Just 3 years ago my husband and I moved, and I have my first garden. I want to tell you that this site saved my clematis. If it was not for research, I would have just pulled it out. One day soon I'll upload an image of my gorgeous Armandi. Anyway, I planted it in September of 2003. It bloomed a little in May 2004 and then this year. The blooms were all over my fence. Absolutely gorgeous! Then in June the leaves started to turn yellow at the tips. Then brown. Then the whole plant started dying. I was frantic. The woman at the nursery was no help. So I followed the instructions to cut it back. MY CLEMATIS IS REVIVED!! I cut it back up to 1 foot from the ground. Around July 1st I saw the little sprout, and now it 5 feet high! I'm so excited. I hope you can save yours to. I'll probably post this on another thread.

Thanks for all this valuable information about C. armandii. They are very hardy plants -- I cut an old one I inherited right back to the roots and it grew back stronger than ever.
My question now is: while my armandii is blooming furiously, it is also sending out new shoots. Can these new shoots be trimmed back? Or should they be left to flower next year?