Answer: If the stems and canes have turned black, they're probably dead. You can determine whether a stem, branch or cane is alive by gently scraping the bark away with your thumbnail. If green tissue is found directly under the bark, that part of the plant is alive. If it's brown (or black) the stem, branch or cane is dead.
Even though some of the canes may be dead, you don't need to discard the entire plant. Wait until new shoots begin growing to decide if there's too much damage. If one entire side of the bush is dead, you may want to plant a new one.
Roses require full sunshine all day, and rich, fast-draining soil. Prune your healthy rose by removing the dead and damaged canes as far back as necessary. Then, remove any suckers that arise from below the graft union, if there is one (the swelling near the base of the plant). Next, select the healthiest canes (thicker and bright green) and cut off the weaker ones. If your roses are just a couple of years old, save about 3-5 canes. Save more on older plants. Lastly, cut the flowering canes back by one-third to one-half. Make your cuts about 1/4" above an outward-facing bud.
Roses need weekly watering to keep them happily growing. An easy way to provide water is to build a basin around the plant above the root mass and fill the basin with water so it can slowly trickle down to the roots. Depending upon weather you may need to water once or twice each week by filling the basin.
Hope your roses regain their health!
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