Go with vinca and you could start some ice plant too that would drape over the edge(although you can cut it back in spring).
Before you replant anything, after you clear out the impatiens (New Guinea?) mix some watersaver beads into the soil. Not too much. Too many will displace and heave the soil. Maybe a teaspoon per quart of soil.
Vinca is great but watch out belooooowwww because it will seed and make babies around the base of your planter you will feel obligated to save and plant elsewhere.

Most temperate zone plants shut down in high temps. Most tropical plants keep going strong but they require more water.

Petunias, Angelonia, Lantana can take the heat and once established need little water.

I second the vote for Lantana. Mine have always laughed in the face of our heat.

Meredith

crazy, from the photo..your beds are elevated 10-12" and on a natural slope.
Is the bed fill natural soil or a mix of natural and bagged amendments?
Do the beds get regular irrigation watering?

I agree with lantana, a good pure yellow mid height as a primary central grouping so the small yellow flowers make a more solid yellow statement.
Still think the hot rose of ice plant ,which is (I guess) a semi-succulent ,surrounding the taller lantana would provide the visual pop to be seen from the road and from inside the house.
Perhaps in an elevated bed of artificial soil, the vinca isn't the best choice but it's a great all season color provider in sunny,well drained ground beds.

Here's some plants that would do well in your beds:

Achillea millefolium
Achillea "Moonshine"
Aromatic aster
Butterfly weed
Baptisia alba
Wine Cups (Callirhoe)
Dianthus
Gaura
Ornamental Oregano
Cumberland Rosemary
Calamintha nepeta
Catmint
Blue Oak Sage
Penstemon

Check out Niche Gardens, Sunlight Gardens, Plant Delights, and Bluestone Perennials. All are excellent online nurseries that between them carry all of these plants. Good luck!

Dottie - I don't think Vinca is a bad choice. I've seen it used plenty of times in difficult areas. I think in some situations it's the only thing that will work. For me though I would save it for the hardest of all places to garden - under large trees in dry shade and bad soil. In raised beds or planters it quickly takes over and dominates everything. But you can't beat it for low maintenance. My favorites are the variegated forms of Vinca major.

It's easy to pick out plants but the key to success will always be how well the soil is conditioned and how much work the gardener is willing to put in. The plants aren't really on the top of the list - everything depends on the health of the soil. This is why I tell people that during extreme periods of drought the thing to do is work on your hardscaping and build up your soil. It isn't the most glamorous part of gardening but it is the key to a great garden.

My yard is so hot and dry that even the weeds are dying!

The soil is a bagged potting mix with some perlite added and yes get's watered with the hose by hand at least twice,three times a day when they look wilty,it's slopey too.Thank you all for your replies..will look into these plants and hope I can find some low maintenance flowers/plants to try..more replies and ideas are welcome :)

Thanks

You could fill them with the colored sweet potato vines - either the dark purple one or the chartreus one. They grow fast in the heat if given enough water.

I would put plants in there that don't need to be watered regularly, like lantana, the ones I listed, culinary Rosemary, lavender, and skullcap (Scutellaria incana and ovata).

Or you could be in some drought tolerant shrubs like Butterfly bush, Caryopteris or rugosa roses, which don't need to be sprayed and can't tolerate being sprayed. OK I've said enough for now. :)

Also, just to be clear, there are two plants with the common name of vinca; a vine, which has a variegated form, comes in taller and lower forms and can be "thuggish", with blue/purplish flowers, and an upright, low-growing bedding plant with white, pink or red flowers. The one will cover ground, and is quite hardy, the other may reseed, but is tender and killed by frost. I think they are the same family, but they sure aren't the same plant!

Knock-Out roses, once watered to establish, and with some judicious watering, would probably do well. Prostrate, or upright, rosemary is another possibility for perennials.

If you want annuals, then callibrachoa/million bells is a thought - they might overwinter, since 4 plants did for me. The lower-growing forms of gomphrena might work, they are quite drought tolerant.

Many of the ornamental grasses are pretty heat- and drought-tolerant - they could be used in the centers of the beds....

TJ...I meant the annual flower 'vinca', not the vine.

crazy..from the photo, it looks as though these beds are road side.
Are they? If so, that's why I suggested the plants I did for maximum color visibility by passing motorists.
Bagged soil in an elevated bed in full sun begs for so much watering because of the sharp drainage plus the heat sink effect of the slate perimeter.
That's why I recommended you get the watersaver beads into the soil before you replant and consider adding in some moisture holding mulch(not bark fines)and regular soil with some clay.

Dottie's right on for a non-stop show of color with the bedding vinca. They can really take the sun and the heat. The water crystals would help to make them less needy about watering though they are not a particularly thirsty plant. Lantana would be more carefree probably. There is a new hardy one out this year lantana camara 'Chapel Hill Yellow' that tops out at 18 inches. Its more of a rambling lantana then upright Miss Huff and much shorter. Its a nice clear yellow. You probably would not have to water very much if we EVER get some REGULAR rain. Adele

Well, another good thing about "that" vinca is that even if the conditions get dry the flowers seem to be the last thing to show it.

OOOoh, the yellow lantana with something taller and purple poking up in the center - like maybe one of the purple leaved dahlias with hot pink/red single flowers.