Hibiscus: Hibiscus grandiflorus in the Cold., 1 by Michael_Ronayne

Michael_Ronayne wrote:
In 2010 I had posted several reports on Hibiscus grandiflorus seeds I had purchased from NWN Nursery - Foster Folly in Chipley, Florida in the fall of 2009.
http://davesgarden.com/products/gwd/c/1826/

The Hibiscus grandiflorus seeds were started indoors without any difficulty. When I put the plants out too early in the spring of 2010 all but one plant was killed by a late frost. The survivor grew a single stalk which flowered and set seeds; the seeds were collected and saved. I posted a picture of one of the flowers here;
http://davesgarden.com/guides/pf/showimage/308992/

With the onset of winter I covered the Hibiscus grandiflorus with one foot of salt-hay and expected the Hibiscus to not make it through the winter in my Zone 6b garden.

Much to my surprise in the first week of May 2010, I discovered that the Hibiscus grandiflorus survived the winter 2010-2011, which set record snow falls in New Jersey, and appeared to be sending up four new stalks. The winter of 2010-2011 saw snow coverage of three to four feet all winter.

I did not remove the single stalk from 2010 which is 50 inches tall so that I would have a point of reference for the four new stalks. As of June 5, 2011 the new stalks are 40 inches tall and the fastest growing Hibiscus in my Zone 6b garden and can be viewed in the attached photograph. I have no explanation as to why a Hibiscus grandiflorus, native to Florida, is doing so well in New Jersey.

Plant Delights (http://www.plantdelights.com/) reports that their Hibiscus grandiflorus cultivar would survive to Zone 6 but I had assumed that they had an unusually cold tolerant cultivar or the claim was wishful thinking on their part. Apparently some or perhaps many Hibiscus grandiflorus are more cold tolerant than is realized. I did save seeds from 2010 so if anyone is interested send me a DM. I also have some interesting hybrids with other Hibiscus species but am still waiting to see how they turn out.

As anyone had any experience with Hibiscus grandiflorus surviving in cold Zones of 7 or less? Was any special action required?

Mike