If you can plant clematis very near something that their roots can grow
under, they're sublimely happy.
A concrete slab, a deck, or on the north or east side of a post set in concrete are all ideal. They like the lime that's in concrete as an added bonus. If none of these are handy, some large slabs of rock or thick chunks of wood set over the root zone will work. A lot of mine are just covered with slabs of firewood.
They can take some time to settle in and be happy, but once they do, they'll grow like crazy.
I had a couple of very nice plants that I set in last spring; they're still only a few inches tall yet this year. Some similar (new last year, and from the same company) plants are blooming, but still haven't reached very high, as of yet. If I could bear to, I'd not let them bloom so they'd go
up. I figure that the only way I'll get tall plants is to either wait patiently
, or depend on those late-bloomers for some height.
First blooms of Kathleen Dunford, new from Brushwood Nursery last year.
(Her roots are covered with a large stepping-stone, and groundcovers
)
raked area behind the shed,had to place some big limestone bricks at the backside of the shed ...ground hogs trying to live under it.... 
Planted 2 flats,of petunias,gave me a shower,then bathed the dog... 
To busy I guess...
