Hungary, being a central European country with a Continental climate is quite unsuitable for growing citrus outside.
However, in the communist period efforts were made to grow oranges in order to replace expensive imported fruit.
In the early 1950's trees were planted in deep trenches, so they could be completely covered in winter. This was mainly on the south-facing slopes bordering Lake Balaton - a large area of water which provides some local modification to the cold winters.
I have just discovered this fascinating page of photos on the web-site of the Elte Botanic Garden in Budapest. It is titled "Hungarian Oranges"
Here are a couple of pictures from it


for full pdf see
http://www.fuveszkert.org/images/pdf/magyar_narancs.pdf
Mike/Citrange

Very interesting technique, however according to this Wikipedia article, so unsuccessful that it spawned a liberal political magazine by the name "Magyar Narancs" (Hungarian Oranges) to refer to the generally goofiness of the Hungarian communist system of that era.

http://en.wikipedia.org/wiki/Magyar_Narancs

Very cool information. Thanks Mike.

Interesting article. Cant't say much for the construction material the communist government used. - Millet (406-)

I have the book which is mentioning about trench culture at Keszthely but I was too lazy to sit down and translate, till now.

The book describe the biology of citrus, the average temperature requirements for growing citrus from flowering till fruit ripening, soil, etc. There are also few data's about hardiness.

The majority of citrus trees were grow from seed until 1951-52 when arrived from Georgia country few thousand of grafted citrus plants like: C. Unshiu, 'New Georgian' Lemon, 'Georgian' Orange, Meyer Lemon and Lemon 'Keszthely' - I believe this one is from seed.

Two rootstock's are mentioned in the book: PT and Bigaradier.

In 1953 Keszthely, the average of temperature to meet the growing requirement of citrus was 199 days and the total temperature received by plants was 3495C degrees. This calorimetry was enough for Satumas fruits to ripen till end of November but not for lemons and orange.

There was done an experiment from 1953 when those tranches were covered with glass from 15th of September until 30th of April and with this method they can increase the growing season to 278 days and the total temperature received by plants to 4.755C. This was enough for lemons and satsumas fruits to ripen in the same year but instead for oranges it wasn't because the intensity of sun is not enough during spring and autumn.

That really worked.

I was there and ate some fruits even.
The fruits very tasty , just very small, at all the lemons ...

With a little of heating this tech would even work perfectly at any place ...

several times .. last time when the comunism broke down