Sun? Shade? North? South?....
Need to know more.
Linda C

If in full sun---Homestead Verbena, purple is a great spreader and the flowers are lovely. Just one plant spreads quickly and in your area, zone 7, it would probably be considered a tender perennial or even better yet, return each year as a perennial? . Here in my zone 6, it's treated as an annual. However to me it's worth the expense of buying each year.

Yes, full sun. The wall faces west. (Sorry, forgot to add that part.)

Paminpa, I will look into Homestead verbena. Thanks for the suggestion. I am still open to other options.

I have a retaining wall that I always plant with wave petunias ... they cascade down and look really wonderful. Plus, waves can take the heat/sun

Do you think they would work with a cement retaining wall as well? I have four huge Austrian pines planted by a former owner and they're about 3 feet above our yard with a retaining wall -- I plant all kinds of perennials and annuals underneath and in the space between, but I would really like to have something flowing over the wall to make it more attractive. How close together would I plant them for that effect?

I have trailing rosemary that likes the sun and heat and not lots of water. it blooms really cute little lavender flowers most of the year. i also love using it for cooking, and the fragrance is wonderful.

Supertunia is another trailing petunia option besides Waves. Avalanche is another. I'm really pleased with my Calibrachoa (million bells) this year, too.

If you want hot colours, don't forget the humble Nasturtium. They come in lots of colours these days in addition to the usual oranges and yellows, e.g.
'Black Velvet' - deep maroon-red with small dark leaves
'Milkmaid' or 'Whirlybird Cream' - buttermilk to primrose
'Cherry rose jewel' - pinky-red and semi-double.
They look best in a poorish soil for maximum flowers without too much coarse foliage. The ones above are fairly dwarf but there are others that come in a range of hot colours, including bicolours, that will trail to 8 feet or more. You can get additional effects by choosing ones with variegated or very dark foliage.

Well, I thought I would give a report, now that it's at the end of the summer season. I went with what I could find, which was double-wave petunias, pink and blue. I ended up putting them in pots, and they were quite disappointing. However, I also planted two in the soil in front of my house, a sunny southern exposure, and they are phenomenal, carpeting an area roughly 2x3' with just those two plants.

Meanwhile, that crazy ivy-leafed morning glory from last year apparently reseeded itself and went absolutely wild. It swarmed up and and over the wooden fence at the top of the retaining wall and then began to spill down over the retaining wall, coming down at least about 8', and overrunning the pots with the petunias along the way. But it doesn't flower much.

Bottom line: Next year, I will try something new. And pull out any morning glory shoots I see.

I have lobelia and nasturtium...both suffer a bit when it is real hot. Dont forget about perennials. There is creeping phlox, soapwort, rockcress on and on. Most of these flower in the late spring though.

I have been looking for a flowering wall flower too. I live in Los Angeles and we are expecting the serious drought conditions to continue, so I need a flowering plant that takes little water, preferably a low maintance plant that constantly is blooming and can withstand 90 degree summers and at coldest 40 degree winter nights. Any suggestions? Is trailing rosemary my best bet or are their more fit, prettier suggestions? The wall will be what neighbors see from the street and what I see when I come home everyday. The wall is in full sun facing north and we have a second wall facing east. it is a big choice!

How about a trailing variety of lantana? It probably wouldn't be hardy for the OP (but neither is petunia) but it certainly can take the heat and is drought tolerant once established. There's a trailing lavender one as well as a white one. There's also New Gold which is...golden yellow.

From what I've read, it would be perennial for L.A.