The hydrangeas will climb the fence nicely but they do not really suit any kind of trellis structure as they don't vine - they attach by rootlets and need a wide, solid surface to attach to. And they really are very bare in winter, being fully deciduous, so offer minimal privacy.

If you let us know where you are located, we might be able to make better suggestions.

Thanks Gardengal. I'm in southern Ontario, Zone 5b.

Dale, there are really no evergreen vine type plants that will be hardy in your zone or enjoy much shade. You would likely be better off planting an evergreen tree or shrub to provide privacy screening in that location. There are a very limited number of broadleaved evergreens that would work in your area but any number of evergreen conifers......like the arborvitae already planted against part of the fence.

If privacy screening in winter is not as critical as it is in summer, you could also use a tall growing deciduous shrub or small tree.

Climbing hydrangea looks like a bunch of roots in winter and is not likely to produce an attractive effect behind your row of arborvitaes - during winter or summer. And is slow to establish. If you just can't stand to wait for your conifers to grow up taller then you would probably be better off spending the money on replacing them with immediately larger specimens than undertaking the cost of erecting a trellis.

A trellis which codes or other limitations may not allow you to go as high with as you may want anyway.

Here is what my climbing Hydrangea looks like on a solid wall in winter - not much of a screen. I have seen photos from someone who trained a climbing hydrangea to a trellis made with wide pieces, but I think it took a lot of training to accomplish the look, and it wouldn't have provided any additional winter screening beyond what the trellis provided.

That is really helpful, thanks! I know that it won't provide total privacy but don't you think it would help to obscure the windows of the house behind?

I would love to plant evergreens but I just can't get them to grow under the maple.

How much sun does this area get? IME it's difficult to grow things below established maples, not just due to the shade, but also due to root competition creating soil that tends to be dry and somewhat lacking in nutrients. I wonder if another vine (or evergreen) that's hardy enough to leave in a very large winter-proof pot year-round might work. IME a shallow saucer will be needed to keep the maple roots from growing up into the container, and some insulation, perhaps in the pot between the soil and pot walls along with bagged leaves piled around the outside, will help keep the winter soil temperature even.

Alternatives:

Have you considered planting something evergreen further out into the yard between the neighbor's house and the windows you will likely be viewing this from? Depending on how you use your yard, that may work.

Do you have limits on what height the fence is? If not, you could add lattice or something, and if you do, would you consider some type of art - perhaps tall or perhaps hanging from the tree to add screening?

Thanks Babs. I think I have been running into the problem you describe around the maple. When I tried to grow cedars there before, they just wouldn't grow. I will have to see what happens with the hydrangea.

The yard is quite small so growing an evergreen between my window and the fence just wouldn't work.

I would love to put lattice up on top of the fence but bylaws limit me to 6' fence height.

I will think about your idea for pots, thanks!

There are some hardy kiwis that might do OK in a pot in your zone, as well as the two related vines, Boston ivy (Parthenocissus tricuspidata) or the native Virginia creeper (Parthenocissus quinquefolia.) I don't know how the kiwis do in shade, but the Boston ivy and Virginia creeper will both do fine in shade. Some folks are sensitive to VC but it hasn't ever created issues for me.

Kiwi - except for the arctic - don't do well in much shade at all and as very large growing vines, generally would need a pretty good sized container to allow the plants to develop a large enough root system to generate a vine large enoughto provide screening. And they have even less of a winter presence than does the hydrangea.

You could try Akebia or chocolate vine. It is supposedly hardy in your area and could even be mostly evergreen in a protected location. And is very shade tolerant. But again, a typically large growing vine needing a large container and a suitably sized support system.

I have frequently attached a 4' trellis to the top of a fence as a line of sight sight screen. With a 4x8 you can increase the fence by 3 to 3.5' taller, and very economically cover 8'. A series of these could do your whole back fence. I attach them by predrilling to not crack trellis wood and using deck screws and electric screwdriver.

A climbing hydrangea is slow growing at first. It gets quite woody, very large, and very heavy, like a Wisteria it might break a lighter to mid duty trellis. Honeysuckle 'Scentsation' or a smaller trumpet vine such as 'Indian Summer' may work better and survive in zone 5b (tbey are rated to 4). They drop their leaves, but might block quite well, except in winter.

If this was my fence I'd pair Honeysuckle 'Scentsation' with Clematis 'Jackmanii' both have a long season and repeat blooming. That also gives you fragrance and hummingbird draw. The honeysuckle also has nice red berries late in the season for visual impact and the other birds. Both grow fast and together you should get enough vine growth to be a decent Winter block.

Here's an internet photo of the in bloom appearance. The light colored honeysuckle really shows up in a twlight garden. And it does get woody too for that forest cottage look.

I'm guessing this honeysuckle would cover about 20' linear. And one Clematis half of that?

I've actually started this pair on my gazebo entrance.

This is pink climbing rose and purple clematis adding 3.5' to a 6' fence using a cedar trellis (the giant Himalayan Lily on the left is 10' tall.

Below I've installed fence top trellis but no vines get along most the fence, even corners.

I'm using a red Japanese maple here and trellis work.

In one location I had started an Alpine Clematis, forming a nice sight block of the nearby neighbor windows.

If there is a neighbor's deck looking down on us, Bamboo or a little Japanese maple works wonders.

Incense Timber Bamboo (Phyllostachys atrovaginata) is SO VERY pretty and rated to zone 5 (be sure to use bamboo ground barrier!).

It's hard to beat a small Japanese maple like 'Purple Ghost', 'Coral Bark' (larger but narrow upright growing), or e.g.., 'Red Emperor' (or another 'Bloodgood' like red maple). I like 'Fireglow' because red light streams through the leaves onto you, if grown in a sunny location ... and it is more sun tolerant than many reds, with an upright ~12' profile.

Thanks GfLeatham for your detailed response. I have tried honeysuckle in this garden and the aphids absolutely destroy it. The honeysuckle/clematis combo is quite pretty.

At this point I'm actually thinking about cutting down the maple and extending the conifers all along the back of the fence. I would then just plant a small tree where the maple is. This should solve all my problems.

Evergreens work all year for you too.

Most of the suggestions offered in the last few posts are unlikely to be very successful in a z5 Canadian (z4 USDA) garden. Just saying............:-)

Yes, I agree. I find that some plants even rated for my zone 5b have trouble, such as an endless summer hydrangea that never re-grows on old growth.

In some of my readings, I ran into another shrub to
consider... a Zone 5, hardy, clumping bamboo called Green Panda (Fargesia
rufa "Green Panda"). Like
other clumping bamboos that do not go beserk and reproduce
uncontrollably, a clumping bamboo is "tamer" than running bamboos (the
invasive ones).

GP produces deep green leaves and green stalks with
orange-red sheaths. It grows 6-8' tall and 8' wide. It tolerates some shade but
requires well drained soil.

http://www.bamboogarden.com/Fargesia%20rufa%20Green%20Panda.htm

Research it and see if this may be something you might like for that spot.

Here Fargesia rufa doesn't get taller than Dale's fence and in really cold winters like the one two years ago dies back to the snow line. It's interesting and a nice contrast in a shrub bed, but not a good screen. I don't remember the variety of mine, so it may not be GP and I am colder than Dale, so he might have better luck with it.