Since I am cursed with a 12-ft. tall South-facing retaining wall, I must mention one caution. South-facing concrete-block or stucco in Southern California can soak up and bounce-back a tremendous amount of heat.

Even in my coastal zone (I can see a bit of the ocean, in the distance) the sun beating on this wall has killed any number of roses.

We have tried various workaround techniques and ideas, but we've never found one that really worked satisfactorily. Here, you can see lattice-work panels. A few inches out from the actual wall, they do help, but bit by bit, age destroys them.

It sounds as if it should be quite pretty! Your space is only about 3' deep, which should be sufficient for one climber. I don't think I would want any tall shrubs because they are going to be happier being thicker than 3'. Whichever climber you choose, please try to select the one with the THINNEST, most pliable canes. From too personal experience, Polka doesn't play well with anyone or anything. You can use its growth instead of rebar to reinforce cement. It has lethal, eagle talon prickles. They are dense, huge and very hard. You WILL sacrifice your blood to it. Add that it wants to devour the world and that should settle that decision. I grew it, or TRIED, on a client's wrought iron fence in Stevenson Ranch, Santa Clarita, for many years. It simply wanted to grow straight up and out in all directions. I am very happy to be far away from that plant. The flowers are beautiful and where it has an enormous space to occupy, it can be gorgeous. As long as SOMEONE ELSE has to battle it.

I can't comment on the Austins you mentioned as I've only grown Margaretta out of the bunch and didn't find it to be all that satisfactory in Newhall. There was too much mildew there, which may have been due to the water stress it experienced. I watered everything in that garden the same and Austins have traditionally shown themselves to be more water needy than most other types in my experience.

Columbines are pretty, but they are so fleeting. You are only going to have color for a few weeks and they do mildew rather badly in the hotter SoCal areas. I grew them in Newhall and the SFV for 30+ years. I had collected every odd type possible from every botanical sale I could find and added all the weird types I could only obtain by seed. They are fun, but only "pretty, when they're pretty". I loved viridiflora and now there is "Chocolate Soldier" to enjoy. I would double think the idea of putting violets anywhere, also. They can be gorgeous and they ARE invasive and immortal. Neither are really suitable for full sun, southern exposure against a stone wall, 3' deep beds. Perhaps a shorter growing Salvia greggii would be a better suggestion? They LOVE the heat they'll get there. They grow quickly so they'll help shade the wall to reduce the reflected/radiated heat. They come in a wide array of colors and they flower nearly year-round. Plus, NOTHING eats them and many people find their scent "minty". They attract hummingbirds, too. Whack them nearly to the ground in fall is about all you really need to do to them and if you want to reduce their mass during the year, whack away. They'll simply thumb their noses at you and rebound with more color. About the only thing easier and more colorful would be the ubiquitous pelargoniums, which can be easy, perpetually colorful and inexpensive landscape alternatives. Here, I have very frequently turned around or entered parking lots to determine what kind of shrub something was, only to find out it was a blamed "geranium"! They really CAN look that good when they are happy. Sure, they'll freeze if there is one, but who cares? It gives you a chance to try another color or something else and they are CHEAP compared to most other plants. And, they root so easily, once you have one, you can pretty much keep it forever.

If those aren't to your liking, there is nothing wrong with filling in the space with plain old alyssum and bedding lobelia. Imagine a sea of sky to ultramarine to cobalt blue with "poofs" of white alyssum at the base of your climber! The alyssum will reseed itself into perpetuity. If the lobelia is happy, it will reseed, too. If not, a couple of six packs of the color (s) you want will fill in nicely. Or, just rotate out densely packed petunias for the warm times and pansies for the cool ones, perhaps with some cool white Icelandic poppies for fun? Sure, there are more "esoteric" choices and you'll cycle through them eventually, but for masses of easy, easily obtainable, non-stop color, these are SO simple. Enjoy!

Thanks Jeri for your thoughts on concrete! Perhaps that’s why the current wall is wood and not stone/concrete! I’ll have to talk to DH about material choice as he wanted to have either brick or stone to avoid having the gate misalign again.

Kim, thank you for helping me avoid a thorny disaster with Polka! I really was thinking that would be a good option because of the colors, so thankful I asked!

And thanks for for your thoughts on the base plants. I like your recommendation of the Salvia, Lobelia, and maybe just rotating annuals.

I have regal and common pelargoniums in the inner yard. I prefer the regal pelargoniums for their fancier flowers, but both get large and mounding if given the chance. The common pelargoniums are each 3-ft around. I wish roses were as easy as these plants!

The problem I see with Pelargonium is the thick root system which I suppose may outcompete those of roses.

Thank you both for sharing your thoughts!

If we replace the wall with another wooden one, does anyone have a good idea for keeping the gate aligned?

Jeri is absolutely correct about the radiated/reflected heat issue. One way to get ahead of the problem is to obtain the largest canned specimen of the desired rose possible. I had an installation in Calabasas where the homeowner insisted he wanted "red climbing roses" on a retaining wall on the west facing side of his back yard. The only way to oblige him within his desired time frame was to obtain three, 15 gal. Red Fountain roses through Green Thumb. Of course he would have preferred something else, but when you have a "cooking surface" you want to slip cover with living tissue during summer, you have to shade it as much as possible and that was with three, large specimen plants. If you don't wish to go that route or don't have that option, you can always obtain the best specimen of the desired rose and then "grow your own", planting it once it has attained as large a size as possible in the 15 gal can. You will definitely want to enlist the services of a gardener or landscaper to install large roses in cans of that size (believe me!). Yes, they're hot and things cook easily, but there ARE ways around many of these issues. Wood can be almost as inhospitable as the stone or cement surface. I don't have anything planted against any of my hotter surfaces (and mine are nowhere near as hot as Jeri's or perhaps yours, though mine can damage plant tissues over hot weekends) but those closest to them have the nastiest cases of spider mites I've seen in ages. Get ready to be washing whatever you plant against that surface with strong streams of water to get the nastiness and debris out of them.