It depends a lot on what root stock the grafted ones are on I would think. And on what variety the rose is too. They'll all react differently to climate conditions.

As for hardiness in cold zones it's six of one, a half dozen of the other. Grafted roses are generally more vigorous because they're on vigorous roots but if not properly planted or protected the bud union can freeze and die and you're left with the root stock. Own root plants are generally slower to develop and a little less vigorous depending on the variety. However, if they die back to the ground but the roots do not die the rose can come back true to variety. So you take your pick and your chances with either.

If you had planted them all in the garden soil last spring, I think you would find there is no hardiness difference due to grafted and own root--especially (for Zone 6 gardeners anyway) if the graft had been planted an inch or so under the soil line. (The graft is the more sensitive point.)

I don't think there would be anything to worry about unless the temps started regularly dropping down to 28 or lower degrees.

The other differences might just be due to the natural hardiness of each type of rose. Not all Austins are created equally cold hardy.

I'm not sure if how long they have been planted in pots makes a difference or not. I always plant in the spring, occasionally as late as mid-summer, but that gives my roses 4 months or more to settle in and develop good roots before the frigid winter temps. Some roses may need more than 2 months to develop a decent root system.

Since there are several factors that might affect roses in pots (how about drainage also?), I think it is mostly coincidence that your grafted plants turned yellow before the own root ones did. But let's see what others have to say on this also.

Kate

If a rose is budded on the laxa understock, there would be no problems with below zero cold. Roses will do fine if some sort of mulch is placed around the pots for protection. Own root roses won't survive any better than grafted ones if the rose is a tender type to start with. One gets the opinion that all say hybrid teas have the same hardiness but many are not hardy unless budded onto a hardy understock.