Monday, April 23, 2012

Another Look At Cold Hardiness In Climbers and Ramblers - Spring 2012

It was almost a year ago that I wrote a piece on cold hardiness of climbers and ramblers. The focus of that piece was to look at dieback at the end of the winter of 2010-2011. This winter, 2011-2012 was one of the mildest winters in the Central NY area. There was very little if any die back. But this spring was bizarre. In March and April, temperatures ranged from the low 20s to almost 90- up and down, within days. Roses leafed out at least a month earlier than they typically do and then were hammered repeatedly with hard frosts. Although the cold wiped out all the buds on my wisterias, it gave me an opportunity to look at how different varieties of roses respond to freezing after leafing out.
I always prune my roses as the forsythia starts to bloom. This year I pruned at least a month earlier than I typically do. There was no difference in how the roses responded to this earlier pruning and later pruning.
Keep in mind, all roses grown here have been selected for cold hardiness and disease resistance. This is what I observed.

·         No roses were killed or had severe dieback from the repeated warming and freezing. It appears that overall cold hardiness is a good indicator of the ability to withstand freezing after leafing out.
·         Roses that had no damage at all to their foliage and canes included all the once blooming ramblers (Rosa multiflora, setigera, beggeriana, spinosissima, arvensis and a some wichurana, rubiginosa and kordesii hybrids).
·         Most of the Canadian Explorers had no damage (Rosa kordesii hybrids). A few had some damage to their tips (Henry Kelsey and Quadra- the only red Explorers).  Unfortunately, the Exploreres do not get as tall as the other climbers and ramblers.
·         The R. kordeseii hybrids varied in their response. Some had no dieback, others had damage just to their new tips, while others had several inches of dieback.  The most resilient ones include: Gelber Engel, Jasmina, Laguna, Morgengruss,  and Manita. They were followed by Aschermittwoch,   Ilse Krohn Superior, Leverkusen, Red Corsair, Rosarium Uetersen, Summer Breeze, Summer Wine.
·         Older, more established roses held up better than roses recently planted.
·         Overall, the most vigorous growers were the most resilient. These roses tend to root the easiest, as well.