I barely cut my Jackmanii back at all this year. Cutting it all the way down has done nothing to make it send up more vines, so this year, I just trimmed the top a bit and called it good. Last year was so hot that the season started a month early. Apparently, Jack didn't like being cut at that point because he sulked for a least another month doing nothing.

I would trim off the dead stuff and leave the rest be. If your end of Z5 is like mine, Jack blooms around the 4th of July. I don't like to mess with that schedule since I have a ton of June & August bloomers. July, not so much.

Cut them back now and fertilize. Jackmanii blooms on new wood, so it does not make any sense to keep leggy wooden vines that will only bloom on their tops.
Rooting Clematis cuttings is extremely difficult and time consuming. Layering was much easier way of propagating for me.

Well, I have two options, it seems. Thanks for the advice! I'll have another look at it and see what I want to do.

I'd cut it back and fertilize it myself but if you want to be conservative you could cut back half the vines and leave the others. I don't like to look at dead stems so I whack my Type IIIs off really short.

It will not hurt it to not prune or to prune late. Pruning just makes them look better/bloom lower/put up more vines from crown.

WOW Sandy ~ how beautiful! Have you kept him in this large pot all these years ~ is there an advantage to container rather than setting him in the ground I only have 6 Clems & 1 is Sweet Autumn.

Very reliable & prolific bloomer ~ Ramona is going through some unexplainable problems this season ~ sigh!

Hi Ditas, The above Jack use to be in a large 15 gal pot but now for the last several years the container is a 1/2 whiskey barrel which is even larger. I find it just easier to control the watering and ferterlizing of the plant. The plant is on the south side of my brick house and it gets full sun and really, really hot and I have a concrete foundation footing that really wicks the water and moisture out of the ground during the hot summer months that I believe it's just best to have it in a 1/2 whiskey barrel. Besides I might like to move it around. It does great, just blooms up high. I will hard prune it after it's first flush and he will do another bloom med summer. Sandy

I have a dozen jackmanii around the place, and some years, I don't cut them back and some years, I do. They still flower on shoots coming from last year's growth, and quickly hide the dead stuff.

The only issue is that they get very, very thick - like 3 feet thick - climbing up a wall. Along a fence, that isn't an issue.

I went out after getting replies and cut away all the old leaves and stems, leaving the new growth. It does have some bare brown stems along the bottom, but the rest looks good, and I think it will bloom nicely along the eave. Thanks for the replies