I have several Austins, including 5 plants of Prospero, which have been in my garden for nearly 20 years and have been pruned to ground level every spring without fail and are doing just fine. I would say there is absolutely no sign of permanent weakening, in fact I suspect the complete annual renewal may well lead to longer-lived plants. It does create differences: my plants take perhaps a week or two longer to achieve their first bloom of the season, and I will probably never see the ultimate shape of a full, mature specimen. But, the plants do increase the number of basal canes and improve their performance every year.

Considering they aren't yet truly established, my guess is that mike may well be correct, but the true answer will depend upon your weather for the rest of the year. If you have a serious drought you will have trouble. Make sure they stay hydrated (moist soil - NOT CONSTANTLY SOAKING WET!) An excellent way to help that out is to keep your roses well mulched with a mulch of an organic material. If this was a "cutting garden" (out back where you were growing them for flowers to cut, rather than for a beautiful landscape), I'd suggest a good straw or hay mulch, but if the beauty of the landscape is an issue, you'd probably be better off with a hardwood, or pine bark, mulch of some kind.

Most years my Austins are cut back that far due to winterkill and I honestly don't notice a difference between them and the ones that don't need much cutting back.

For most of the Austins you have it should not be an issue especially since your in zone 5 - re: permanent weakening.

However Evelyn would be the only one I would suggest is the most susceptible to repeated die downs over the years. The rest Glamis Castle, Mary Rose, Eglantyne and Brother Cadfael should have no issues in zone 5 - been growing them all in zone 3 and all of them die to the mulch line here but still comeback. Eglantyne is the most resistant.

Evelyn however turns to mush even below the protection line and never achieves it's original 1st year planting vigor as received from a zone 5 vendor.

Thanks for all the responses. Some HT growers in our neighborhood use plastic cones for winter protection. I'm wondering if any of you do the same for DA shrubs or OGR's. Of course, they would have to be pruned down far enough for the boxes to fit over them, so perhaps defeat the purpose... This year I mounded soil around the base of the plants and then covered with a deep layer of chopped oak leaves. It worked well (I had started to uncover when the devastating freeze hit), but what alot of work to undo in the spring! Anybody use these boxes or anything of the kind for their DA's or OGR's?

Work it is but your numbers are small so just peck away at it so it's not that much work. I normally protect about 400 to 500 roses in a en mass method that varies from my usual peat moss covering and burlap to last years cheap frost blankets. Fall and spring covering, uncovering and cleanup sessions combined are about 10 to 15 full days of work.

I use pseudo rose cones (old large nursery pots) for some of my small OGRS (gallicas and young Damasks) and it cuts down on cane death but not always. When I want to get cane length I find bending and pegging down the flexible caned roses in fall and then burying works to a degree. On the whole more length is saved than just mounding - but you get canker loss and it is more work in the fall being impaled on thorns. This does not work for saving fall Hybrid Tea cane length as nearly all of them have canes too stiff to bend down.

The basic tenant is if you want cane length saved by the method the more you will save the closer the out of zone rose is to your zone. In other words I get good cane survival for zone 4 and 5 roses but beyond that it is tremendously iffy. For example I have made Marechael Niel survive for 3 winter now, but no cane survival, it just comes back but to 1/10 the normal 3 year height of the rose.

Truth be known being in zone 5 should allow you to have reasonable success with a lot of the old classical European OGRs with minimal protection if you have lots of snow.