your plants do NOT look like they are lacking anything in the way of fert ...

blame the whims of ma nature ...

actually though.. now that you have me thinking of this in 2 different posts ... there is usually a lull in august ... perhaps they are just getting ready for that last fall burst.. and your expectation is the only problem ...

i always hesitate to try not to fix.. what might not be broken ... lets drop all the double negatives ... dont fix it if its not broken ...

ken

Although, you might wish to be enjoying these as container plants, would you instead be able to plant them directly in the ground where they'd be happy to have their roots to run freely!

Are they in full sun?

That sure is a fine specimen of 'HF Young' !! ... I'd only recommend up sizing the pot on 'Princess Diana' and 'VV' and of course keeping them well fed as you're doing, next year just might be a whole lot better! I have 'Princess Diana' and it's a lovely variety that's for sure, mine had pined away though and now am reestablishing the plant.

Getgoing, you do a great job on a balcony! That clematis is so nice and full.

Frozenbudd, I just moved the VV/princess diana combo from a 4ish gallon pot to this 5 gallon pot which is several inches deeper than the previous pot so that should keep them happy for a bit. I am just not sure how many 15/20 gallon pots I can have on that balcony (got 2) before the condo goes all up in arms against me. :)
Prairiemoon, this hf young clematis has some really good genes. It gave me several blooms in its very first year starting from a bagged little plug!

GGoing - I love performers. I have bought a number of clematis, but they seem to get lost in the shuffle. So many things to do, that they seem to be an afterthought for me. I barely get the rest of the chores done in spring and anything growing vertically gets the short end of the stick I'm afraid. I keep hoping one of these years I'll be ahead of the game and do better with them. That looks like a great Clematis and I like the color. It seems to me if I were gardening on a balcony, I'd love to have something grow that well and cover so much vertical space. Looks like a great decision.

Are they sharing a pot? Both have the potential to be good sized plants.

IME both of these bloom less fully but for a longer period than HF Young. Also IME, clematis really only start to reach full potential at year 3 or 4, so I wouldn’t worry.

yes they are in it together. :) I guess I am just going to have to wait for better display next year. They are in a 5 gallon pot. They will get a bigger one when it starts to get root bound in it..

I think I would probably try to separate them. As is, one is likely to outgrow the other and then you will only have one clematis in the pot anyway.

One thing that may reduce weight is super light weight containers. They look much like other containers, but are made of molded foam. You will still have the weight of planting media and the plants, but at least the pot won’t add much weight.

You are probably right about the two of them not getting along too well. I guess I will separate them in late winter/spring when they are supposed to be pruned- almost all but a few inches of growth is supposed to be removed which means I will not have to untangle the foliage at least..