Your answer is yes...and no. Yes, when grown with everything they require to be healthy and vigorous, and given the shelter to prevent unnecessary damage from extremes at either end of the weather spectrum, they will perform to their fullest, genetically set abilities.

No, in that nothing you can do is going to change what was programmed into them genetically at conception. You can push zones by insulating them through deeper planting; mulching; winter protecting; keeping them healthy, full of foliage, well fed and watered; even planting them close to hard scape which acts as a thermal collector, radiating the absorbed heat back to them, preventing frost from being as hard or as damaging as it may have been. But, that doesn't change what the rose is genetically capable of. Move it to a less ideal situation and stop protecting it and it will respond as it's supposed to. Kim

I have to agree with every thing Kim said but I have a question for you. Where are you getting your zone information from? I know HMF lists zones for all of the roses but sometimes those are just default settings and not from the experiences of growers. If you don't post your zone and that you are growing and successfully wintering these roses no one else will know that the rose is indeed hardy to zone 4-5.

I have noticed that if there is ice on the canes, I have worse luck than when (like this winter) we had 2 feet of snow and 14 below F. That ice is a killer. It can occur when it is not even that cold.

Exception rugosas and rugosa hybrids of course.

Zone hardiness is not the only determining factor for how a rose overwinters. For instance, roses that are perfectly hardy on paper in my "zone" can sometimes succumb if we've had our usual warm fall weather followed by a "surprise" nor'easter that plunges the temperature down by as much as 60 degrees overnight. From 80 to 20 does some serious and often fatal damage to a rose - zone 7 or no zone 7. So look to your weather patterns as well as just your zone. If you live in an area where autumns are Disneyland perfect, a gradual cooling down until winter, then your roses are very lucky indeed....Also, ice should be no more a problem then snow, since an ice coated cane can't get any colder then - well - ice. But if the cane hasn't been allowed to properly harden off, then damage may occur....Maryl

If you grow them well each season, the root mass increases, so they come back with stronger growth after the annual severe pruning.

Digger Dave in z. 4a Montana grew HTs that looked really strong by mid-season, but he said it took years to build them up to that. He had hardly any cane survival, so it's not really a case of becoming hardier.

However, if you have any cane survival owing to snow cover or whatever, second-year cane stubs will be hardier than green, first year canes and will have a better chance of surviving the next winter.

Yes and No and much as MichaelG just added.

You will not change the inherent baseline genetic hardiness of a given rose variety. However, a specific rose variety will reach its true hardiness potential only after a few years of establishment and root growth.

To site one of many possible examples, I've had a couple of Lavender Lassies for a good few years now. In their first year of planting, they died pretty close to the ground after the first average winter. The next year, they were about 50% winter hardy. By year 3 and beyond, with more establishment, root growth and larger and thicker hardened canes, they are nearly tip hardy in all but the worst winters here.

Thank you all for these great responses ! Growing roses in MN is always a real challenge, I have learned from the mistakes I made. A rose will not necessarily get hardier, but with the proper planting (the craft a couple of inches below the soil level, even an own rootstock goes in deeper), a cooler fall into a cold winter, no spring frost, a nice layer a snow (2 feet plus) and a lot of luck will help a lot growing beautiful roses in the upper midwest. Plus, like Seil mentioned, who knows if a rose is not hardy for this zone unless you try it.

The responses are all great. I emphasize keeping the roses healthy during the year which involves a good fungicidal spray program, and occasional application of insecticide, as needed. I try to keep a thick mulch cover.

I also have many of my roses bordering a sidewalk and driveway and shoot the snow onto them during the winter for winter cover. I cover (with wood chips) only those that seem to be more fragile. Most are not covered, other than with snow. As they mature and grow larger and healthier, they are better prepared to overwinter.

Now back to roses. Up here in the southern Smokies I was told it was to cold during the winter to grow anything on fortuniana root stock. I have learned that if you can get them through the first winter, it does quite well with winter protection. 1/2 of my garden is on fortuniana root stock. The roses themself seem to be stronger then some on Dr. Huey. I use a thick cover of oak leafs as winter protection. Also I have learned to see were my roses are originally bred. Roses bred in a cold climate will probably winter well. Roses bred in warm climates are iffy at best.

Also some hybrid teas are hardier than others; for example, Olympiad, Savoy Hotel, and Warm Wishes are relatively hardy.

Back when we commonly had sub-zero temperatures, I lost a bunch of white roses to winter kill. However, Garden Party was cane hardy.

I agree, Michael, my Garden Party sails through winter and it's in a pot! Green nearly to the tips every spring. Other ones that are very good winteres for me are, Folklore, Memorial Day, Oklahoma, Hondo, Grenada and surprisingly the florist rose Red Intuition! Double Delight winters but starts out short every year due to die back.

My Garden Party is launching a campaign to take over the neighborhood. If we take any sort of vacation away from the house for a few days, she just might succeed.