In MN, no experience with the Clethera. The diervilla is nice, but it does need a shear midsummer to refresh the foliage if it's in full sun. The sorbaria, like sem, is also very pretty but it runs.

Why aren’t you considering evergreens if it’s the bare winter you’re concerned with? Or at least shrubs that have winter interest, like hydrangeas or red twig dogwood?

Clethra needs moisture and is late to leaf out.

"Or at least shrubs that have winter interest, like hydrangeas or red twig dogwood?"

It's a narrow strip right up against the back of the house; it's not prime viewing real estate out the window in the winter, and I have to be careful not to plant anything too large or too wide. Red twig dogwood is way too large, and I already have a lot of hydrangeas, am looking for something different. An evergreen that is going to get tall enough to add visual interest in the growing season is going to get too large for the area or be a shape that just won't work there (e.g. pyramidal dwarf Alberta spruce or those tall columnar shapes).

Clethra needs moisture and is late to leaf out.

Well, the good news is moisture isn't a problem in this area -- it's not overly moist, but neither is it dry; I'm blessed with well-draining, loamy soil for the most part. How late is late? Are we talking early to mid May, or going into June or later?

In NY zone 7 mine leaf out in June.

Oh wow, June!?!? Forget about it, then.

Clethra is a plant for acidic soil, and that seems to be non-negotiable. I've tried in several times, in several places, including the swamp, and it's never lasted more than a year or two.

Clethra is crossed off the the list...

I could also consider "Iceberg Alley" sageleaf willow. I have one in another part of the back and it's doing great. That silvery foliage is really eye-catching, too.

Ilex verticillata and symphoricarpus are winter favourites. And corylopsis, hamamelis, wintersweet. I am really just beginning to dip my toes into shrub world after initially filling my tiny garden, then having to take them all out. I am changing over from massive roses to mannerly shrubs at the allotment too...so also eagerly awaiting tips and suggestions.

I always have time for firethorn.

I will second pennlake that false spirea runs. According to Morton Arboretum, it is colony forming. https://mortonarb.org/plant-and-protect/trees-and-plants/false-spirea/

That was true in my garden and we finally got it out,... I didn't really think it was pretty personally, but maybe mine was a less ornamental variety.

My comments are based on experience: i dont find clethra easy to keep ” tidy looking ” The interioir branches go every which way and . it looks messy for the long period. before it flowers.

”sem” does run and leaves ugly sticks to trim back in spring

my 2 cents on DAS- overused, gets spider mites

this space:

Q exposure?

Q access ti irrigation?

Q do snow & ice slide off the roof onto it?

Q clarify its dimensions again: w x l

1 what im wondering is do you really need to work on yet another area of your already huge garden?

2 do you use the deck in the bare season?

3 since woodies( deciduous or conifer) never stop growing it seems any kind of tree will eventually out grow the space

4. who sees this space? if its not visible to the public couldnt you live with a mix of tough attractive perrenials? : that big tall polygonatum commutatum, amsonia hubreckii, polymorpha, ( giant fleeceflower) rampant shastas or feverfew,

5 or just perhaps, let it be and enjoy gin and tonics on the deck with your back to the offending sliver of real estate.

I’d go with #5…

Q exposure? Southern.

Q access ti irrigation? Yes.

Q do snow & ice slide off the roof onto it? Not that I've noticed.

Q clarify its dimensions again: w x l: 3-4' wide max x 3-5' tall preferred.

1 what im wondering is do you really need to work on yet another area of your already huge garden? Do any of us NEED to LOL!

5 or just perhaps, let it be and enjoy gin and tonics on the deck with your back to the offending sliver of real estate. I look out this bank of windows a lot. My sight line is just past it, but I do look down. And I also see it in full view everytime I go down that path, which is pretty much daily all season. Read: It's bugging me.

If you like the texture of a sorbaria but don't want the running look at Matcha Ball. New growth isn't quite as colorful as the other cultivars on the market, but it stays put. Other thing I like about sorbaria, for a deciduous foundation shrub, is it leafs out very early in the season and holds well into the fall.

I’ve looked thru my pics to try and find some suggestions, but can find any that fit your size requirements. I know you said you’ve already got hydrangeas, but it sounds like they’d be perfect there. Of course I’m a hydrangea lover and feel you can never have too many lol (having almost 50 myself)….

Update w/pics in original post.

Proof….hydrangeas can help any bed!!

😀