In my own garden, compacted clay soil that was not properly dug and amended has been worse for my clematis than root competition though to be truthful, some of those spots weren't properly dug and amended because of arborvitae and Douglas fir roots....

Those that I just hacked out holes for still struggle even ten years down the road than those that went into established beds that were originally rototilled and amended.

Without seeing the situation firsthand, I can't say for certain but I highly doubt the Nikkos are the problem. They are just too small a shrub to offer any significant root competition. The vast majority of clematis at my old garden were planted to scramble up various shrubs and trees (so quite close to the base of the plants) and virtually without exception root competition from the shrubs and trees was never an issue.

Like BorS, my first inclination would be that the planting hole was not as adequately prepared as would be preferred. I'd prune the vines back hard, apply some alfalfa meal to the root zone and mulch well with a high quality organic mulch - compost would be my preference. In addition to being an organic fertilizer, the alfalfa meal will stimulate basal growth or the development of new stems from the root grown.

Hi,

These planting holes were really well prepared and, I think, are well maintained. Holes were dug at least 2 ft. deep and filled with a mix of composted manure, peat moss, bone meal and the upper part of the original soil. Clematises are pruned back hard every spring, dressed with composted manure every spring and every fall, and fed Epsoma rose fertilizer every two weeks they are not in bloom. I also give them seaweed fertilizer from time to time. Clematises in other parts of my garden, not fronted with deutzia, thrive with this preparation and maintenance.

But buyorsell brings up an interesting point: the difference in performance between clematises planted in a meticulously prepared hole in an uncultivated bed and others in identical holes in thoroughly cultivated beds. I have done a tour of my property since receiving that email, and indeed the clematises I planted within perennial borders (usually on a tuteur) are wonderful specimens about which I have no complaint, and those planted in well prepared, but isolated, holes are not doing as well.

I think I'll wait a couple of days hoping for a few more clematis addicts to chime in here, then carefully dig out one deutzia and see if I can ascertain how much mischief it's doing.

Thanks for your input. It will all be used in the end!

IF you dig a hole in clay and then plant in amendments you basically create a pot...they can become potbound in such a situation.

I fear that makes sense. I don't have a terrible clay situation, though. My community is on a pretty steep hill, and my street is at the bottom of the hill. Over hundreds of years, much of the top soil seems to have worked its way downwards, and the people on my street are the beneficiaries. I do have some clay but not huge hunks of it. It's probably the best soil I've ever had.

Still, the clematises holes are a lot finer than the surrounding soil, and I can see where the clematises might have become potbound. Certainly something has happened!

If you think it is a diffuse root problem, I would not hesitate to dig it up and examine for whatever signs of damage might be found. The roots can be trimmed and the vine potted, while looking at the hole and surrounding area. As a test, if you add water to the hole, using a hose and find water does not drain, the reason is hard pan. Trees living in places with shallow hard pans will spread roots laterally, searching for preferential watering sites and can provide significant root competition. Digging in the hole, tree roots are larger & when pulled up, lead to the culprit. Sometimes in digging up a vine I've found nothing wrong with the roots, leading me to conclude the site was just not getting enough sun and other times finding the roots severely damaged beyond my wildest guess.

Did you figure out the problem?
What did you do?
How are the clems now?