I posted your question at the Clematis forum, and linked it back here. I hope some of the experts there will answer soon.

Here is a link that might be useful: Clematis forum

It does need to be trimmed back....there is plenty of info over at the garden web...Do a search and you will know more than you ever wanted to know...

http://forums.gardenweb.com/forums/load/clematis/msg0618453824084.html

http://forums.gardenweb.com/forums/load/clematis/msg0518350512328.html

It depends on the type of Clematis.

Mine is a Purple Jack-something?? It isn't as big as yours, but was all brown like that and this is what it looks like today (sorry - took the pic from an upstairs window). I didn't trim mine at all.

{{!gwi}}

I would cut it back.
Is there a lot of new growth at the stem of the old stuff?
If so I would cut above it.
For that matter, I'd cut it back to about six inches to a foot from the ground then water the heck out of it.

Lori

Patti, what color was the blossoms? That would give a better idea of what type they are, and how far to cut them back. They like to have something covering their roots, to hold the moisture in. I'd cut it back like Lori said, but to about 1 foot. It'll thicken it up. I've got two sending up new shoots already a foot high, and 1 in front that isn't doing a think yet. :( I'm not giving up on it yet.
Leslie

I don't know much about them but sure do love 'em. ALL of mine climb like mad. I have to tie them to the trellis or arbor when they're still too short to "grab" on to something or they fall over too.
Suzi

I forgot to tell you this little rule of thumb.
1st year they sleep.
2nd year they creep.
3rd year they leap.
Leslie

Leslie..last year was the third or fourth...I've just never done anything with it because I didn't know what to do.

Mine is a dark purple the flowers are only four petals and not a real large flower. I wasn't very happy with what kind I ended up with so I've planted another one in there that is white with pink center. I planted it late so if it grew last year I don't know. It didn't bloom if it did.

Anxious to see if I find some white flowers in the mix.

I didn't cut anything back last year and it did super..

Don't know if I should leave it or what...but it is crawling to the ground. Aparently the windmill base I have it growing on isn't enough...I wish I could cut just the part that is growing down but that is all intertwined with the other part...and it is pulling it all down.

Yours sounds like what I have. The link below gives instructions for pruning. Good luck with it.

Here is a link that might be useful: Clematis Jackmanii

Patti, I only live a couple hours from you so maybe what I do will work. Trim the dry growth off of them in the early spring before the new growth gets going. You might be able to do that now if they new sprouts are short. The old wood is the strongest and thats what I use as my guide. The older taller wood is usually wrapped around the support and I will leave it if there is good growth. If the vine seems unstable I'll cut it back or use a large twist tie to prop it in place. Once late spring arrives it will take life of its own and start wrapping itself up the support again. If it loves the soil where you have it, fine a good large support for a bigger plant. If the plant is trimmed and the old flowers plucked off, it usually will show more flowers in the fall. Keep the clematis feet in the shade and the head in the sun.

I have never trimmed mine didn't know I was supposed to but it is not even that big....it was here when we moved in so this is it's 4th year maybe it will take off or maybe if I had trimmed it would help? Can't now ours is already blooming...Stacy

You've probably gotten more than enough advice here but just thought I'd add mine. I have a friend that grows lots of clematis and she whacks them back to the ground. She use to didn't but she said when she started pruning them severely, she's gotten more growth and blooms than when she left it alone. I'm sure too it depends on the variety, exposure, etc., etc.

There's 3 groups, of clematis. I have a Sweet Autumn. It has heavy growth every year, and thousands of little tiny white star-like flowers, that smell heavenly. I don't cut it back, mainly because it's at the cabin, and is already growing before I get up there. A couple of years ago, I did cut it back and it didn't hurt a thing, but I haven't cut it back since.

Here's a Jackmanii. I couldn't bring the picture, so here's a link. It's a group 3. While you don't HAVE to prune it back, it'll probably do better if you did. I have a group 3 that's a Hagley Hybred, and I think the rabbits chewed threw the stems, clear down to like 4-6" from the ground, last year too, and it's coming back gangbusters. That's why they say to plant the crown below the soil line when you plant it. So if it gets weed whacked or injured somehow, it'll still come back.
Actually the feet in the shade and head in the sun rule is to conserve moisture for the root system. I usually cover the root area with some broken pot pieces or some flat stones.
Leslie

Here is a link that might be useful: Jackmanii

When I lived up north, I had many clematis. No matter what kind, I would cut them down in the spring to just where all the new growth was coming. This was usually 6-12 inches. Even though some of the mostly dead-looking stalks may have a bit of growth, it's going to look bad if you don't cut it off.
The cut off stalks will put out new growth at the bottom. Good luck.

I have two and have never cut them back. If you cut them to the ground then it will take a lot longer for them to grow back up the trellis as mine have new shoots on the old wood. One is facing the south and one is facing the west and they both are doing well. Plus I don't feed them anything either. I met a lady in the garden section of a store once that was looking at clematis's and she mentioned that hers is always way behind the neighbors for growing and blooming. I asked her if she cut it down each fall and she said yes...I told her not to as that was the reason for the slow progress.