Move to England.
Just kidding.

It's just too hot for them here. My Double Delight rose bush is seven years old now, and every rose on it today was crispy and black on the edges of the petals. I cut them all off. Water just won't do it when it's this hot. That said, you should try soaking them with the hose, since their water requirements rise with the heat.

In my experience, there are a few roses that do well in the summer heat here, including St. Patrick's, Marilyn Monroe, Iceberg, and Henry Fonda.

Most people in California plant tropicals in the spring and everything else in the fall, so that the plants can become established before our brutal summer heat hits them.

Cone flower, a prairie flower, does not do well in most areas of California. Here's a thread on the issue from earlier in the year.

Good luck.

Renee

Here is a link that might be useful: Echinaceas: fussy for you?

I agree with Renee, it's just hot. I'd clip off all buds and give your plants a break. They're still trying to get established.

Be careful not to overwater and make things worse. I think it's more the sun at this point. Can you give them some temporary shade? Get an umbrella out there? Or throw some shade cloth over them?

I've been adding shade for my plants this week. I have a little piece of leftover fencing that I stapled some shade cloth to. It can be stuck in the ground or leaned on a plant in a pinch.

I went to the landfill here in San Diego and made bags of the best mulch just the other day. Had previously added compost and bark but the ground was still hot but now the ground holds the moisture and stays cooler. Ground cover succulents are now blooming along with sweet william around my roses which also holds moisture and look colorful.
My backyard is at the base of a mountain so I get animals that like to eat roses so this year I left them tall when cutting back and the animals ate most of the lower half of the bushes while the tops look great. I do put a little Mira grow for roses in a spray once a week now that it is so hot. Never wet the top of the plants because the leaves will just fry. Also the snails this year are in the plant and I find them in brown leaves and some grasshoppers.

Have you dug down in the soil a bit to see if it's wet all the way down? Maybe they are just having trouble getting established in the heat.

I have some white iceberg roses which I hardly water at all, not more than once a week--or even that, but they're well established..about 5 or 6 years. They bloom almost year-round in my zone.

The problem might be that the plants may have just been planted at the wrong time of year, after it already started to heat up in your zone. Almost anything planted "late" needs more water than usual to get it through the heat.

An initial deep soak when planting natives is di rigeur, but I'm beginning to think that may also apply to almost anything else--at least here in Calfornia.

It also seems that often when plants are on a drip or irrigation system of some type, they tend to be watered shallowly more often which keeps plants' roots from going "down" where they can survive a heat spell. It might not be too late to do a deep soak, and then back off and do longer, deeper waterings less often. I had a tree that was in the ground for two years that looked pretty shabby and I was ready to yank it. I did a deep soak and then started doing soaks once a week, and then stretched it out to every 2 weeks over time. It looks much better...like it will survive now.

As a side note, I LOL'd at the thread, "echinaceas fussy for you?", because like the OP, I have never had any luck with echinaceas or coneflowers. Davissue, in the thread, said they require more water than their drought-tolerant reputation would lead you to believe. I think she's right.

I think the problem with echninaceas (and some other popular 'drought-resistant' perennials) is that in most areas of the country, their idea of drought = 6 weeks without rain.

They have no idea what it's like to live in CA and see no rain for 6 MONTHS, lol.

My double delight looks crispy too. They just do in the heat.

My new plane trees seem to like the heat. They're making new buds.

I never had luck with echinacea.

Thanks for all the great answers. I sense a deep soak may be in order here.

I would like to second the good ideas already mentioned. Make sure the soil is deeply moistened. Mulch to reduce soil temperature and reduce surface evaporation. Shade to reduce heat stress on the plants. I really like the shade idea. I grow woodland plants under 50% shade cloth, in a full sun location. They love it. I'll bet your plants would need a lot less water if they were in the shade. But the shade can't come from a tree; it has to be a shade house of some sort. Trees take way too much water out of the ground.

Are your plants exposed to hot dry winds? Try building a wind break.

Try growing plants on the east side of the house. They will get full sun in the morning when it's cool, and shade in the hot afternoon.

Don't over-fertilize, especially a plant that is not well established. You can burn the roots.

If you over-water, you can waterlog the soil, which drives the air out. Without oxygen, the roots cannot absorb water. So a waterlogged soil can cause wilting. This happens a lot with house plants that are potted up in overly dense mix.

I agree with the deep watering. I will also say that I have had problems with drip irrigation and gophers. The gophers make tunnels and the water from the drip irrigation (most types of irrigation other than flood) finds its way into them and then follows them away from the plants. It can be wet under the dripper and bone dry everywhere else. Also, if you have fast draining soil, you might need twice as many drippers because the water doesn't spread much in the soil.

I have found that when it is my watering day and I put my finger down in the dirt under the roses that they are still nice and moist especially now with all the mulch I just put on plus the worm castings hoes deep into the soil. Here in San Diego where it has been in the 90's everything is looking really great with lots of roses. There are roses that I own which grow better in the spring but continue to look great as green shrubs but with fewer blooms.
Yesterday when I went to the Home Depot and saw all the beautiful flowers which would probably fry in this heat but if you look up and notice the shade cloth and the continuous watering those plants were destined to fail in our gardens.
My neighbors have wells around all their plants but she loves to water but her plants are crunchy with a lot of disease which I had also before just applying Bayer 3in 1. It's just criminal to get the leaves wet and than they fry in the sun. Do the mulch thing and the Bayer and remember to feel the moisture in the soil.
A house up the street was vacant and weeds up to your ears but the roses were green still with some blooms and that was when I realized that they must like the stress and not to overwater.

Different varieties also tolerate drought differently.

I planted some rose bushes and a few perennials some weeks ago

They probably were not established enough before the summer heat hit. Plants do best here planted in the fall or winter, which gives them as long as possible to grow roots before the heat hits with a vengence. Keep them well watered to get through the summer, and they'll look a lot better next year. One thing you can do is apply a thick mulch of compost or composted shredded bark (leave a few inches of space between the base of the plant and the mulch, to prevent disease). Mulch helps hold moisture in, and keeps the soil cooler, which is of great benefit to the plants.