Clematis are generally one of the most manageable vines you can have. They CAN get big, but they can also be cut back severely every year is you want to. If you go that way, come back and ask me to link a good site about pruning them—different types get pruned differently—and I don’t have time right now to find the link.

They’re one of the few vines that don’t sucker, so it won’t be spreading anywhere other than where you planted it—no problem with it growing under the fence! I found out when I was looking for something to grow up my privacy lattice that virtually all of the other vines are definitely, or can become invasive. When I get around to it I’m gonna be putting in some clematis to grow up the lattice!

I recommend you put up a trellis or a lattice a few inches away from the fence and grow it up that. Clematis are great growing on trellises, and that would keep it from trying to sneak thru the cracks in the fence! The only way I can imagine it would become a problem is since you’re planting it on the north side of the fence, it might keep trying to grow "toward the south" for the sun! But if it’s on a trellis with a little bit of clearance between it and the fence, you could easily "redirect" it or snip off wayward stems.

Gotta go! If you want that clematis link let me know and I’ll be back in a couple days.

Skybird

It will benefit from something more to cling to than just the fence, and something I've found that works well up against a fence (or against anything really) is chicken wire type fencing. You can buy it by the roll at hardware stores. I'll try to upload a couple of pictures so you can see an example. It pretty much disappears against cedar fencing, though you can see it in these pictures where it's against our garage.

And I now have 3 separate vines that have grown from seed out in the flower beds. There are from jackmani, and come true for flower type. The seeds take something like 6 months to germinate.......

All in all, about 3 years after planting one, they are spectacular.

I have 4 clematis of several common varieties, similarly along the north facing side of my southern back yard fence. These went in after my neighbor chopped out the Virginia creeper. I think this will be their 4th or maybe 5th year. They’re off to a great start this spring, and there are lots of blooms already on them that will start opening within the next week or two.
Keep in mind that clematis climb by wrapping the stem of a leaf around something skinny. The main stems do not wrap or wind around things like some other vines do, like a pole bean. If the leaf stems can’t find anything to wrap around, the whole vine just falls down. They like to wrap around something about the size of a pencil or thinner. There’s no way they can climb the fence without something like that to climb. If you look carefully at Almond’s picture, you can see a couple of the leaf stems have wrapped, and you can certainly see how tall and straight the main stem is. It isn’t curling around anything at all, and is not particularly inclined to go behind her wire fence at all. Without leaf stems wrapping, it would just fall.
For mine, I went to H.D. and bought a long roll of 3 foot wire fence, with squares about the same size as that seen in Almond’s post above, but this fence is coated in some kind of green plastic. The green stuff helps it just disappear into the background behind the vine, and helps keep it from rusting. I cut 6 foot lengths of the stuff, and then cut each lengthwise. I bent each 6’x1.5’ piece length wise into a low semi-circle. So when I stood it up vertically against the fence above each newly planted clematis, it stands out 3 or 4 inches from the fence at the middle, allowing the vine to easily grow both in front and behind it, and allowing the leaves to easily wrap around the green coated wires. I then used my staple gun to staple each side to the fence. I think if the wires were up close to the fence the leaves wouldn’t be able to wrap, and the vines would just fall down unless I trained them purposefully or used ties to tie them up. It worked great, and now that the clematis are taller than the fence, you really can’t even see the green wire trellis. It just disappears into the greenery of the vine.
I don’t think any part of the vine sticks through the cracks in the fence. Only the part at the top can be seen by my neighbor. I don’t think there would be any need to put screen up the side of your fence to keep the vine from getting through the cracks. Clematis are not that vigorous. You should EASILY be able to just pinch off, or retrieve any bit of vine which you can see is sticking through. I’ve never done this, and I really don’t think ANY part of my clematis vines is sticking through the cracks. I’ll check when I get home this evening, and let you know.
The clematis seem to like the location. With the angle of my fence line, as the saying goes, "They’re feet are in the cool shade, and their heads are in the sun". They go to the top, and then sort of spills over a foot or two with blooms on both sides of the fence. I’m pretty pleased, with them. I’ll try to do a pic later this week if I can find time.

Be patient. Mine didn’t reach the top of the fence till spring of the 3rd year.

Good luck,
Bruce

The site is linked below. This is a really excellent site for everything I’ve ever had to look up regarding clematis. I’m linking the home page for access to all the different info, so just click on the pruning link on top.

The information you’ll find describes the three "different types" of clematis and how and when to prune them. This site is from the UK, tho, and where they say to prune the group 3 ones hard in February, I’d probably modify that to sometime in March! But you still get the basic info.

If you don’t know what you have, generic pruning directions would be to prune as much or as little as you want to soon after they finish blooming. And clematis, like most things, will fill in more – bush out more, if they’re "pinched," so when it’s small I recommend pinching it (snip the tip of each stem off just above a leaf joint) every time it grows a couple sets of new leaves on each stem. It’ll probably take longer to produce flowers, but that way you’ll have a lot more stems producing the flowers when it does bloom.

If you go to the A-Z part of the site and look up any individual clematis, it will tell you what "type" it is. If yours is one with a smaller purple flower ones, you most likely have Jackmanii—the one David is talking about. It’s pretty common, and it’s a group 3 type which will get pretty barren looking on the bottom if it’s not cut back at least every now and then. Since you don’t really know what yours is, you should be able to tell what type it is when it finally starts blooming by the size of the flowers and when it blooms.

If you want to look at some pretty pictures, look up Candida and Henryi! They’re two of the ones I want to get. HUGE white flowers—dinner plate size. The first one is all white, and the second one has dark anthers for wonderful contrast.

One more thing I almost forgot! When you’re working with clematis—planting, tying up, pruning—you may see stems that look like they’re broken in half! They’re not! Clematis stems (the older ones) have a hard "bark" exterior with a soft stem that runs loosely thru the middle of it. The outer "stem" can look completely broken—but the soft stem inside can still be just fine, so don’t freak out if it looks like the stems are breaking or broken. Look more closely, and very probably the inside stem is still fine and it will keep growing regardless of what the "outside" looks like. (When I first started working with clematis I thought the "broken" stems were—well—broken! I was pruning them all off—until I stopped to look closely enough one time and realized there wasn’t anything actually wrong with them!)

If you start looking thru the pics on this site, you’ll want them all!

Good luck with yours—and with your neighbor!

Skybird

P.S. Here’s another one I want some day!