Florida Sieboldii and Cassis are not hardy in your zone. They haven't been hardy in my zone! I've lost three sieboldii and two cassis.

Save yourself money and heartache and don't plant them and especially not from seed. Clematis don't breed true from seeds and they take years to grow to blooming size from seeds.

Jackmanni should be cut back every early spring.

Canadian zones are not the same as US zones. If I remember correctly, Canadian zones start counting at zero, US zones start at one. So, your zone 5b is equivalent to US zone 4b.

Greems, we're in the same zone, and I have many clematis that do well here. If I had room I would have more!

Most clematis are hardy enough for our zone - you just happened to choose some of the few that aren't:)

Here's my list - all from plants, none from seed. As it is they take 3 years to really get going (more for type II); I can't imagine waiting for SEEDS to put on a respectable show...

Jackmani Superba
Serenata? (unknown from my sister)
Harlow Carr
Emilia Plater
Venosa Violacea
Perle D'azur
HF Young
Yukikomachi
Polish spirit
Snow Queen
Princess Diana
Arabella
Betty Corning
Blue Angel
Piluu
Abundance
Gillian Blades
Victoria
Josephine
Comptesse Buchaud
Guernsey Cream
Ice Blue

Check some of these out on Clematis on the Web

http://www.clematis.hull.ac.uk/new-clemalphasearch.cfm

I'm sure you'll find some that you like. Good luck!

Judith

This might sound silly but how do the clematis ever reach their potential height if one cuts them back every year?

Greems, you'll be astounded at how much growth happens in April and May! Every year I vow to stay on top of the vines and trying to direct them, but to no avail - they always end up doing whatever they want to! Believe me, they have no problem, after the third year or so, reaching their potential height! You cut Type III's back to 12" every year, but Type II's only the first couple of years to encourage more canes.

By the way, no question is silly....ask away!

Judith