Hi,

a few pictures of my unprotected Citrus hybrids after this long but not extreme winter.

http://img97.imageshack.us/img97/4238/hamlinxfd2.jpg

HamlinXFlying dragon is one of the best. Citrumelos are dead and Citsumas are severely damaged. Citrus ichangensis seems to be harder than any Poncirus-hybrid.
/Robert

http://img28.imageshack.us/img28/7998/citrumelo.jpg
http://img697.imageshack.us/img697/8002/citsuma.jpg

how cold did it get?

I've got to respectably disagree with you on that one. There are many well documented cases of people growing citrus in 7b zones with great success but only a few varieties worth eating will grow in this zone. My favorites that WILL grow in this zone are satsumas, nippon orangequat, yuzu, taiwaniquat, yuzuquat, keraji mandarin, changsha mandarin, C. Taiwanica-Nansho Daidai, and Ichang Papeda (ornamental). Growing citrus in this zone will take alot of care. One of the things that I think alot of people are doing that jeopardizes there chances of success is that they give the plant to much nitrogen and/or the give the plant nitrogen to late in the season which makes the plant grow succulent tender plant growth and makes the whole plant more vulnerable to low temperatures.

Robert,
I think you are pushing too much. From my experience hardy hybrids should be grown at least two years more before planting outside, than be protected for the first year. Only after such maturation the comparisons could be made.
The climates in Europe and USA are so different that USDA zones are only very rough approximate. This is specially true for hybrid citruses that are difficult to keep under weeks of frozen ground.

are, that I did not supply nitrogen after end of August. I do not feed much some of my plants are quite old (8 years) and not higher than 30cm (1inch). They should be very hard in fact. there was no plant younger than 4 years. I have to admit I did not even try to protect my Citrus plants -they had to take what came. But this winter was not extraordinary cold. I think it fits into the USDA 7b pattern but I am in doubt that we can compare US 7b with European 7b. The same digits but a lot of differences. Maybe the whole system does not fit European climate?
For sure it is not at all possible zu grow Sasuma without protection in Vienna. Not even in a Vienna City-Garden (which should be 8a)
I am always talking about results without protection because one can do everything to protect plants. There are people in Germany who build houses around their palmtrees etc.
I have one hope that the scion of my sweet Citsuma has survived. If yes this could show me the way how to act in future. I have budded the Citsuma on the top of a 1m Poncirus. Maybe this is the answer: keep them well above ground. Most of the damages appeared near the root base.
/Robert

Whenever the temperatures are forecast to drop below 20F it is time to build a frame around your citrus tree and cover with frost cloth and provide a heat source under the cover. I grow citrus trees and in the 1980s there were freezes that dropped the temperature to as low as14F despite warm water surroundings and very warm microclimate and still had damage even to Satsuma trees! The temperature dropped to extreme lows even in Tampico, Mexico in the December 1989 freeze! There is no other place on Earth that gets this cold at this latitude 23 N!



The December 1989 freeze nearly wiped out the entire trout(weak fish) stock and it took over a decade for it to recover from this disaster.


I am moving to either Guam, Brazil, or Miami, Florida. Guam 12N and Brazil rarely have severe freezes like the December 1989 freeze. In North America, you must be extremely far south even further south than 23N to escape the really severe freezes.

Hi Ilya,

you are right I was quite rude with my plants. Some will probably survive and I will dare another try.
/Robert

Robert, Citsuma seems pretty healthy..

This decade there should be new citrus hardy to below 10F with advancement in genetics. The mechanism for cold injury is already understood and the genes that determine cold tolerance are known. It could happen in the next five years, but it will take time to propagate the increased cold tolerant citrus.

Tri,

I would like to share your optimism, but am not sure that you are right.

The agricultural revolutions are happening very rarely and only if there is an economic drive for them.
Actually , the freeze resistant citrus could be easily bred by conventional means during 100 years since Swingle hybrizations with poncirus.

Outside conspiracy explanations there is no economic interest in such varieties. Citrus industry have no interest in expansion outside of traditional areas; consumers are not ready to change from traditional varieties and decorative tree market is too small.

Concerning the understanding of freeze/stress resistance we are not yet there. Dozens of genes are cloned, but their interactions and detailed mechanism of resistance is not elucidated. Total sequence of clementine genome is under way but is not yet finished.

I estimate that we are at least 30 years before emerging of resistant citruses

I have been surprised at the cold tolerance of my sister's Owari satsumas--on their own roots. They survived mid teens with no protection and little damage--for several nights. There are not a lot of citrus that taste better either.