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Leaf drop signals time to protect most roses
Kansas
Many roses in Great Plains gardens are semi-hardy. Without protection against freeze-thaw cycles and bitterly cold weather, their winter kill becomes a very real possibility.
But, the time to provide that protection continues to provoke arguments in gardening circles, according to Greg Eyestone, associate director of the Kansas State University Gardens.
"The fact is, it doesn't matter when you protect roses in late fall unless you get a real cold snap before the plants have conditioned themselves for cooler temperatures. Roses will go dormant when they're ready to, protected or not," said Eyestone, who also is a K-State Research and Extension horticulturist.
The problem with protecting roses too early is that the mulch will look like ideal nesting material to rodents on the hunt for a winter home, he said. Then the roses themselves will become part of the critters' winter food. And, even if the damage isn't killing, it will become a window of opportunity for a wide range of rose diseases the following spring.
"That is why it is better to delay until we have had some cold weather--at least a hard frost--so the rodents will have found other places to live. By that time, the roses will have lost most of their leaves and started entering dormancy. In Kansas, that usually means around Thanksgiving," Eyestone said.
Knowing which roses need protection can be tricky, though, because most roses are grafted onto another variety's root stock. The area where the upper, named rose plant and the other variety's root stock were grown or grafted together in the nursery often looks somewhat scarred.
"In most cases, the root stock will be very hardy. So, what gardeners really need to know is the hardiness of the grafted part. They've got to know the genetics," he explained.
Generally speaking, though, most shrubby floribunda roses are hardy, Eyestone said. Most of the large-flowering, always-popular hybrid tea roses are semi-hardy in the central and northern United States. Most grandifloras--which tend to look like unusually tall hybrid teas, but produce clusters of smaller flowers--are also subject to winter kill. Whether climbing roses are semi-hardy depends on the variety.
"The Don Juan climber, for example, is not winter hardy. If you mound up soil around its trunk for winter protection, it will die back to that mound," the horticulturist said. "But the New Dawn rose is very hardy, so you might leave it unprotected. Or, if you wanted to ensure you have really long canes next year, you might bend them over and protect them through winter."
When rose growers are unsure about their plants' hardiness, they basically have two options, Eyestone said. They can treat all the roses as if they were semi-hardy--which won't harm those that could make it through winter on their own. Or, growers can do some investigation.
Protecting roses basically comes down to installing insulation around each plant's graft zone to even out winter's temperature extremes and keep the plant dormant until early spring (when the insulation should come off). This insulation can be a mound of wood chips; compost; straw; crushed fall leaves; or even loose, well-drained soil. The recommended height for this mound of organic material is 10 to 12 inches.
Spraying the roses first with a fungicide can be a good idea, though, Eyestone said. Pruning long canes to 24 inches from the ground can help prevent winter wind injury.
For gardeners interested in investigating their roses' genetics, the plants' original plant tag is a good place to start, he added. Even so, a garden store that sells the involved varieties can often provide more detailed guidance. Libraries may have in-depth resources on roses. The World Wide Web includes information, as well, including a site called www.helpmefind.com, which is an illustrated plant database that lists more than 35,000 rose, peony and clematis varieties.
Date: 11/24/04
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