I have 2 own-root roses - Erinnerung an Brod and 'Perpetual' White Moss that just won't grow. They have been in the ground for 2-3 years in my Zone 9b yard, and they've just done nothing - no die-back, but no growth either. Erinnerung an Brod is said to do well in hot climates per HelpMeFind, but it's not for me. Don't know if Zone 9b is too hot for 'Perpetual' White Moss or not, but for me it's living just not thriving.

I dug them both up and discovered that they haven't grown above ground because their roots haven't grown at all.

I have put them in a bucket with some water and root stimulator and hope that will help them to grow roots, but I was wondering if anyone had any ideas on how to get roots to start growing.

Not all Zone 9b are the same. I grew Perpetual White Moss in Zone 9b Newhall, CA central desert and it grew and flowered beautifully. Something else is amiss. Can you photograph the area in which they weren't happy to give some perspective about the prevailing conditions in that position and please indicate where you are. That old 9b had a 100+ degree temperature swing summer to winter (15F to 115+F) and could have a more than 50 degree temperature swing from midnight to noon (50F to 100F). THIS 9b (Central CA coast) is a chilly coastal area with severe marine influence with a bit over 50 degrees swing winter to summer and an average 25 degree swing midnight to noon. Obtaining a fuller picture of what was going on where they were planted will definitely assist in helping you figure out what was going on with them.

The dozens of roses (of all sorts) next to/near them are fine. It's just these 2 whose roots, it turns out, for some reason haven't grown.

OK, some things which might produce the mystery you are experiencing:

Something was dumped into the soil where these two roses were planted which inhibited their root growth and is different from what's under the others. Think paint, oil, that kind of thing. (Can't determine without excavating the area to see what, if anything, is wrong with the soil there.)

There is a large rock or chunk of concrete under where they were planted which inhibited their roots from burrowing deeper into the soil to support their maturation. (Can't determine without excavating the spots to determine if there is something down there.)

The spot where those two plants receives more reflected, radiated heat than the others, cooking the moisture out of them, which prevented them from developing where the others don't get the same heat inhibition. (Can't determine without seeing the position and its proximity to any hardscape upon which direct sun may shine and reflect from.)

Something is preventing the irrigation water from reaching those two plants in the same amounts as the other roses. (Requires investigating to determine if they are receiving adequate irrigation)

There's a tree root under where they are the others don't have to deal with that robbed them of moisture and nutrients. (Again, need to dig around to determine)

The soil in that spot is just badly drained or too sandy which can inhibit root and plant growth due to bad or too quick drainage.

Those two plants were more shaded than the others around them so they received insufficient light.

The roots of those plants have been eaten or severely disturbed by a gopher, vole or mole where the others weren't.

The roots of those two plants have been attacked by crown gall. Only a visual inspection of the roots can make that determination.

There are likely other potential issues but those will, at least, give you some things to explore.

Are they own root or grafted?

Own root, as are all my other roses.

The great majority of my roses are healthy, and I have/have had a few that are/were not - yellowing stems, die-back etc.

But these 2 are unusual - they appear healthy - no yellowing, no die-back, no black spot, but also no growth because for some reason their roots aren't growing. Before I dug them up (and saw how small their root balls are) they were both near roses that are doing quite well so I don't think it's due to their location etc.

They have been in the ground for 2-3 years so have had plenty of time to develop roots. I'm hoping that rooting hormone will help, but I am curious to see if anyone else has had this experience - a healthy rose (in an environment full of healthy roses that do grow) that just won't grow.

When my roses fail to grow but look healthy, I often blame it on shade and tree roots. Is either a possibility for yours?

Don't think so. They got plenty of sun and there were no tree roots near them when I dug them up. I have only one large tree in my yard and it is 20+feet away from where they were planted. Plus roses near them (and in a few cases closer to the big tree) are fine.

It's really a mystery to me.

I would plant the rose in pot till Fall and watch the development if any.