Abutilons? They are very easy to train flat,flower all year and like the summer shade winter sun if its not TOO much sun. You could plant a mix of them in red or white or orange or yellow...sort like those Bougainvillea plantings of mixed colors. Just an idea.

They need regular watering.

We're also in SoCal. How deep is the planting area in question? We've grown Abutilons as small trees (love them) that did well in filtered light. Our Iceburg Rose bushes are in full sun year round. We don't have Bougainvillea now but have in the past...also in full sun where they are very showy. Just hate the thorns. For a trellis vine, a Bower is a huge favorite that do well in filtered light. They have shiny, lacy leaves with trumpet-shaped blooms but need growing room to be optimum. Maybe take your photos to a local nursery for suggestions.

Just looking at your birch trees. Keep an eye on them for birch borers that have become an issue here. We've lost several of our birches due to those freakin critters. :-(

I would even consider a non planting solution. These are the kinds of situations that would traditionally be solved with a bas relief sculpture, a trompe l'oeil mural, or something like that.

Right...the narrow appearance of the area in question is why I'd check with a good nursery.

A bit overdone, but heavenly bamboo can grow tall but not too wide. Nandina.

Tall but somewhat narrow glazed ceramic pots in the color of your choice filled with whatever seasonal color appeals and compliments the containers. They should be high enough off the ground that the bunnies can't easily reach. Lime green pots with orange gerberas; cobalt blue pots with red and whte geraniums.....etc. River/beach rock to cover the soil and fill the remaining space. Or use a groundcover if you prefer.

Another alternative is a very columnar shrub, like Ilex crenata 'Sky Pencil' or Cupressus macrocarpa 'Wilma Goldcrest'.

There are any number of viable solutions for these areas but you may need to get a little creative or do a little searching for suitable plant material

socks, I love the colors of Heavenly Bamboo. Ours are mostly all in shade with those pretty red clusters of berries. Just wonder if the narrow pathway in the pic here could be too narrow for them to look their best. Ours are kind of full.

Consider xeriscape

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chloebud - I'm reading that heavenly bamboo is invasive...?

Not to my knowledge. Some bamboo is invasive, but not the heavenly. It is very pretty when it gets the berries and when the leaves show color. A very adaptable plant in my opinion.

It IS considered invasive but only in certain areas of the country, primarily in the southeast and midAtlantic states.

We're in Southern CA, and our Heavenly Bamboo isn't the least bit invasive. socks is right...the colors in the leaves along with the bright red berries are downright stunning in certain light IMO.

Nandina is Heavenly Bamboo

Yes...Nandina and not really a bamboo but an evergreen shrub. The berries are supposed to be toxic from what I remember. I've often thought about clipping some leaves/berries for display but no thanks! Too bad since the berries on ours are orange during the fall and red at Christmas. We have 8 HB shrubs that are all in mostly shade or filtered light.

Found this photo and other info online...

"All parts of the plant are poisonous, containing compounds that decompose to produce hydrogen cyanide, and could potentially be fatal if ingested. The plant is placed in Toxicity Category 4, the category "generally considered non-toxic to humans", but the berries are considered toxic to cats and grazing animals. Excessive consumption of the berries will kill birds such as cedar waxwings, because they are subject to cyanide toxicosis, resulting in death to multiple individuals at one time. The berries also contain alkaloids such as nantenine, which is used in scientific research as an antidote to MDMA (ecstasy)."