I will have to leave it to someone who gardens in a climate more similar to yours than mine is to help you with the rooting method, Jen, but this is callusing. See the granular, white swelling around the edge of these cutting bottoms? That is callus. It is where the cambium layer, the circulatory system of the rose has been exposed to conditions suitable to encourage it to differentiate, to perform like stem cells, begin becoming what is needed to support the plant. That callus can become several different things. If the piece is budded to another rose piece and the cambium of both plants is in good contact with each other, it knits together, becomes one, producing a new circulatory path so the inserted piece begins growing as if it is part of the piece that has roots. That's what happens when a rose is budded or grafted.

It can become scar tissue to seal over, heal, a wound. Once these cuttings were put under soil, the conditions triggered that callus to begin forming root tissues so the plant could sustain itself through its own roots. The callus is simply the circulatory system readying itself for whatever is needed of it, then waiting to be exposed to the proper stimuli to trigger it into becoming what is best needed by the cutting. I hope it helps. Kim

Thanks, Frances, for the link to Kim's burrito method. That looks like a winner. I can't wait to try it.

Jen, there are a lot of different ways that work best for various zones. I used to live on the hot humid Gulf coast & could NEVER get rose cuttings to root, even though I rooted many other plants. I never got the "baggie" method to work, even though neighbors did.

What worked for me:
1. Use coarse media--very coarse. I use #3 sandblasting sand. It's about the grain size of grits. I add ~1/3 ground coir.

2. Use a stronger rooting hormone. I'm using Rhizopan #3, which is 3% IBA--it greatly improved my take.

3. If you want a vast improvement & are rooting a lot of cuttings (and this helps for all woody cuttings like your gardenias) put your rooting area in a high sun place & use mist. This might be counter intuitive, but the more sun, the more the leaves can work & support the cuttings while they're forming roots. The heat is good, too.

You can set up a pretty effective amateur mist system cheaply. I use one of those "porch cooler" or "kennel cooler" mist lines you can get for ~$15 at a Home Depot or Lowe's.
It's a 10' line with 6 brass mist heads screwed in. Has another 5' or so of attached tubing fitted with a standard hose-end connection.
You don't HAVE to add a timer, but you'll want to. I'm using a Raindrip 675 CT ordered from Amazon for ~$30. It's not as fine tuned as a professional would use (one that lets you select a few seconds each minute) but it's pretty effective.

Just 3 dials, battery operated:
A manual dial--set to run at will, for however long you choose.
A dial for how often it comes on, in hours. (I have mine at the most frequent time--on this timer, 1 hour)
A dial for how many minutes the water runs. (I'm running it 10-15 minutes per hour, shutting off at sundown)

Tie up your mist line on rebar stakes or whatever, so that the heads are ~18" above the cuttings & the mist drifts horizontally over their leaves.

For me, cutting failure is always due to rot. Using coarse media drains off excessive water & rooting under mist in full sun keeps the leaves on the stems & actively growing to supply energy to the stems that are trying to push roots.

Any bottom heat helps a lot also. Kippy is taking advantage of a hot cement slab under her cuttings. I used to use a hot bed for late fall/winter rooting. It's similar to a cold frame, but packed with rotting hay & manure that generates warmth under the cuttings.

Hope this is helpful--keep trying. There IS a way that will work for your climate & by experimenting, you'll find it. Maybe this will work for you.

It also seems everyone finds some varieties easy, some near impossible. I personally find species & many modern roses difficult. Chinas, teas, polys--a lot of the ogrs root well, & fast. And, as you observed, some roses root better in different seasons.

Here's a view of my mist area in late afternoon (it's getting shaded at this time, but most of the day it's in full sun)

That is very much the "home made" version of the old mist table that worked perfectly for many years at The Huntington. You often don't need the mist at night, unless there are hot, strong winds and high aridity at night. Putting the cuttings in the sun where the foliage works (as bluegirl correctly theorized) and applying the mist to prevent the cuttings from failing due to water loss (no roots to absorb it) pushes them to grow the root system they need to survive. Brilliant! Congratulations! Kim

Many thanks!--but it's not my idea. Years ago, Bax Boyd posted these suggestions on his "make more roses" webpage.

They were the things that turned it around for me & let me root most ogrs successfully. Still difficult with many moderns.

But the baggie method that so many friends (even those in the same zone!) use--I can rarely get to work. The cuttings rot.

They all rot under bags here, too. Kim

Thanks, everybody!! I have learned a lot about growing cuttings, and I really, really appreciate the help! I am writing all this information down. I am going to try to do this next year, it is unusually cold here already.
Jen