I doubt that is planted too deep since it is suggested that most clematis (not the fibrous rooted Atragene group) are planted several inches deeper than the growth point where roots meet stems. Planting deeper will encourage it to it grow more stems. I also don't think there is likely too much compost. As for the iron, magnesium, and Osmocote, I don't add that type of amendment without having a soil test that tells me it is needed. Some amendments can be a problem if they build up in the soil. It looks very close to the concrete wall which seems to be crumbling a bit, so I would begin with a soil test that includes pH and basic nutrients to see what is available to the plant. Often your state extension service does these for a fee.

What direction is the wall facing? In your area, that wall may be really hot in summer if it is unshaded and south facing, which may stress a young plant. Evenly moist soil but good drainage is really important for clematis, so you can put your finger deep into the soil to see if it meets that requirement before deciding whether to water or not. Being under the eaves may give them less moisture from the sky or less snow for winter protection.

IME some clematis take longer to get their feet under them than others, and this clematis has only been in the ground one growing season. How large was it when planted? If less than a gallon or three, I wouldn't necessarily expect it to be very large at this point, even if others are. In my garden some clematis have taken off quickly, but others have taken a full 3 seasons to really get rolling. IME some of the early large-flowered clematis are more difficult to keep happy than others. Etoile Violette is a much easier to grow plant.

It’s an east facing wall; in summer at this elevation that’s 6-8 hrs of sun/day so the wall probably does get hot. I kept a small potted plant there to keep the roots cool. Should I put a little potted tree in front of Suzy Mac instead to help cool the wall until she creates enough shade?

This one was hard to find and ended up being quite small. What worries me is that there is only a single vine this year. I could have been over enthusiastic about planting deeply so I’ll poke around and see. How much would she hate being dug up if it comes to that?

It’s high time I do some soil testing here so I’ll get that done. Soil here is heavy and tends to have a high ph so I mulch with a lot of organic matter. How specific does the ph need to be for a finicky clem?

Thanks so much for your detailed response!

Kay

Oh, should I prune down that single vine?

Kay

I might check around to see how large the root system is and if still small, plant it in good potting soil in a large pot, but if it has a large root system, just leave it. It sounds like it might be a soil issue. Did you turn in a lot of compost or other organic matter around the whole area when you planted it rather than just planting it in what was there? It may be the photo, but If the root system is small enough to replant, I would move it a couple of feet away from the wall. Put the trellis midway between the wall and the plant. That will get it further away from the hot wall and the added alkalinity from the concrete.

i don't know what to say about pruning it at this point since I don't have a lot of early large-flowered clematis.

NHBabs, you’ve been so helpful already; I hope you don’t mind a couple more questions.

It was hard to feel the size of the root system through the clay. The system felt small so I dug it up (gently) and put it in water for a few minutes. The soil fell away easily and I was surprised to see A pretty good sized root system.

There are these little roots developing a little ways up the stem that make me think it was a little too deep. I think there was only one other little stem developing down by the main root and it was broken off. The other stem is an old one that has no signs of new growth.

Since it was out of the ground I went ahead and put it in a 3 gallon pot to pamper awhile. This is a pretty shady spot and the next week is going to be cool weather.

You asked if I planted it with a lot of compost and organic matter. I probably threw some in the hole and probably didn’t dig a wide hole. The soil was certainly thick and heavy. So when the time comes, do I want to plant it in the environment that is there or do lots of amending? I guess I leave it in the pot until it seems stable and growing well?

Thank you!

Kay

that looks great, 4" deep is perfect. Give it some alfalfa to encourage additional shoots up from the buried crown. Pinch out the tips of the vines you do have now. Clematis are the exception to the rule to plant in native soil. Dig a wide and deep hole and amend with compost and organic matter. Mulch. Don't worry about "shade" all that means is they like moist soil not that they actually have to be shaded. Nurseries grow them in black pots in full sun by the acre....