The cold-hardy varieties developed by Drs. Ackerman, Parks and Clifford (the Winter Series and a few others) and Camellia Forest Nursery (April Series) allow people in your zone (6) to plant camellias in the ground. That is the limit though. I have not seen any that is officially advertised for Zone 5. Camellia Forest Nursery's website can be seen by clicking here. You can also call Nuccio's Nursery for additional varieties at 626-794-3383 (sorry, they do not have a website).

Luis

Here is a link that might be useful: Very Cold Hardy Camellias

Here are a few links that I collected when researching cold-hardy camellias. Hope these help some.

http://www.sazanka.org/ackerman/index.htm
http://www.bcnursery.com/listItems.asp?displayType=Across&Cat=CAMELLIA&CatDesc=Camellias&SubCat=20&SubCatDesc=Camellias&Search=Link
http://www.monrovia.com/PlantInf.nsf/PlantThumbsAv?SearchView&Query=field+botanical+contains+camellia&Count=10
http://members.aol.com/camsoc1/ACKERMANCOLDHARDYVARIETIES.htm
http://www.cspv.org/ackerman.htm
http://camellia-ics.org/_ics/ackerm1.htm

The cold hardy camellias we generally understand are C. japonica or C. oleifera hybrids. Many do not familiar with some camellia species which are very cold hardy, growing at high mountain, ranging from 6,000 to 10,000 feet elevation. The plant can be loaded with flowers at 2 to 3&1/2 inches in diameter also with neat leaves. Although the flower is single but the petals and texture are very attractive. I am very sure in near future that the new cold-hardy hybrids camellias are coming. The flowers will be simi-double, in deep pink or red. The new flower will be larger.

Here is a flower picture of C. tenuvalvis, Shell pink at 3&1/2 inches. It grows at 10,000 feet elevation at Sichuan Province in China discovered in 1989. Notice the pollen and anthers are in wine red. The flower is not that shabby. At end of June, the flower buds are well formed. I am very sure this camellia will stand cold.

Here is a link that might be useful: {{gwi:510717}}

I have been growing Camelia japonica in Northeast Jersey for several years now. I plant them near my house (zone 7) and never have any damage overwintering them. Note that they are sheltered from strong sun and winds. Mine usually bloom in March or April. Go for it.

Does anybody know a source for C. tenuvalvis? That's a beautiful plant.

It might be a few years of waiting after special camellia nursery or research institution has done their investgation, hybridization or propagation.