Hi Blue Gardener!💙
So sorry you are having trouble with your clems. I am not an expert by any means, but I have a few suggestions I've learned from others over the years that may help.
1. The best clematis to grow in Zone 5 and lower is the Type 3 variety which bloom on new wood (i.e. In the Spring you can whack the type 3s off to less than a foot above the ground and they will send up fresh, new shoots and blooms! Type 2 clematis bloom on old wood/vines from the previous year during their first flush in the Spring and will bloom a second time if you cut them back after they bloom in Spring. The cold temps of zone 5 make it challenging for old vines to survive and thrive. ( which means fewer blooms)
To look up Type 3 (or "green") clematis easily I use the Brushwood Nursery website as you can search by type and zone. Out of the clems you listed above, Jackmani is the only Type 3.
Out of the Type 3 variety I have found the viticellas to be the hardiest and most floriferous. Venosa Violacea is one of my favorites.
2. Sun and soil both factor into flower production. Clematis like sunny locations and rich, well drained soil. They also need consistent watering. If the soil is too dry it will impact your blooms. Also, it helps to bury your Type 2 clems deeper (I bury down to the second set of leaves). This will help protect the roots so the plant can bounce back if if it gets clematis wilt. Viticellas rarely have issues with clematis wilt (another reason why I love them)
3. Clematis are heavy feeders. The best fertilizer is rose food (you can also use tomato fertilizer). Ratios of at least 10-10-10 will help you get more blooms. I feed in early Spring and continue to reapply every 6 weeks or so. I believe Yum yum is a ratio of 2-1-1.
4. Potted clematis need a cold hardiness of 2 zones less than where you live to do well (i.e. If you are in zone 5a then look for clematis zoned for 3a if you plan to put them in pots long-term). It also helps to put potted clems in a garage over winter (or you can try turning the planter on its' side- I've heard this works but haven't tried it). This is to avoid the freeze thaw cycle that can occur in planters over the winter (esp. when there isn't snow cover).
I hope that helps! Clematis are one of my favorite plants to grow, but it took me a while to find my groove. Happy gardening!💜 Julie
