For what it's worth, our temps have been in the upper 90's and low 100's and I have had at least the first 3 cuttings I stuck take root. They were stuck about 3 weeks ago and all 3 have roots. Two of the three have a bit of top growth as well. I'm sure it's not ideal, but I believe it is doable.

I just stuck mine in a potting soil mixture, watered them in, and placed 2 liter bottles over them.

I'm sure someone who knows far more than me will chime in, but that has been my experience so far. Oh, and the pots are on my covered porch that only gets indirect sunlight.

I have been sticking cuttings in the ground around the parent plant and they seem to be rooting. These are old or own root roses, I haven't tried it on hybrids.
Barbie

Mine rot. Try in September/October. In Wasco (California's big commercial rose growing region) they strike all the own root roses in the fall when they get the valley fogs. The fog keeps the cuttings moist, but the soil is still warm enough to get them to root.

How to Root Roses...
as told to me by our local "rose witch", Venessa, who grows gorgeous roses:

Use clear plastic cups with plantable peat pots inside for "liners".

This way, you can see roots forming without removing the little rose from the cup & disturbing it, & then when you plant the rose, peat pot & all, into a larger pot, there's almost no disturbance to the tiny roots.

Poke drainage holes in the bottom of the plastic cup.

Use coconut coir, available at pet stores, for the rooting medium.

Break apart the coir brick & soak it in a bucket of water.
When it's saturated, put it in the peat pot, put the peat pot inside the clear container, & use a pencil to make "post holes" in the rooting medium (the coir).

Take a cutting from the growing tip of a rose (one that hasn't already been cut).

Remove most of the leaves, including any tender new growth, leaving only a few at the top.

Using a knife or the blade of a pair of scissors, gently scrape off the "skin" below that first node, & submerge the cutting in water & cut it again about 1" below a node or joint.

This fills the cut end with water instead of air, so that the little cutting can uptake water without being stopped up by a "cork" of air.

You can also split the end where the stem is cut.

What you're doing here is exposing as much inner tissue as possible to the rooting hormone & the medium:

The inner tissue is the part that forms roots.

Dip the scraped area in a rooting hormone & gently tap off the excess (too much will burn the cutting).

Gently put the cutting into one of your "post holes"
(if you just stick the cutting into the coir, you may scrape off the rooting hormone), then gently tap the coir back into place around the cutting.

Spritz the cutting with water, & keep it in a warm shady spot until you see roots through the sides of the cup.

Use a clear plastic cover to keep the humidity high.

(I don't have one of those, so I just put the roses in the shade & keep them spritzed;
easy enough, since I check them every day anyway.)

As soon as you see roots, prepare a "real" pot with good potting soil & re-plant your rose, still in its now-soggy peat pot, in that.

Baby your rose until it grows up somewhat;
this will be an "own-root" rose, & its root system won't grow as vigorously as the grafted varieties that we buy in the nurseries or mail order places.

The roses that I rooted last summer are still in pots, & I protect them from the worst of our heat.

They should be ready to plant next spring.

If you want to root some roses this summer, go right ahead:
the ones that are rooted in the warm months will do fine.

If you start them too late in the year, they aren't strong enough to last over the winter.

On a misting table sure you can root in summer.

What is a misting table? Thanks.