"although the average temperature at Sepp Holzer’s farm is 39.5 degrees (4.2 degrees Celsius), sometimes plunging to thirteen degrees below zero during the winter, his one hundred acre property known as the Krameterhof is home to 30,000 fruit trees, including many citrus."

From: http://hines.blogspot.com/2012/01/interview-with-permaculture-farmer-sepp.html

I've heard he grows all his citrus from seed, the non-hardy die, the survivors benefit from very strong microclimates. Anyone know what's going on over at his place in Austria? I'm curious where he's getting his seeds

Hahaha ...

Well, if nobody noticed, I am AUSTRIAN and of course know him ...

He gets the seeds from supermarket fruits and his permaculture is great, but about citrus you cannot copy anything ...

I was thinking of you when I posted this!
Have you had the opportunity to visit his farm? Can his method not be copied because it relies on having his mountains?

He lives within the alps ... that place has an enormous amount of rain and snow.
The first frost means the first snow.
Therefore his citrus are buried under some meters snow all the winter and never have to suffer lower themperatures than 0 ° C.
Besides is on the south side of a high mountain and he plants them between giant rocks.
That rocks load up with heat and give it away very slowly.
So he has a microclima that does not stress Citrus at all and gives him rich harvest in growing season even.

Well, now you have the detail:

Under the SNOW ...

Thank you Sanguinello, I have to admit that I'm surprised a lemon can handle being buried in the snow for months, but what works is true. I've tried burying much hardier plants like rosemary in snow and in the spring they are dead. Shoveling snow onto a plant might be less ideal...maybe it packs too much, or maybe it's just that rosemary likes light?

Rosemary is complicated .. I think what it really kills is too much wetness, for the roots are very sensible and used to dryness.

Anyways, I saw often rosemary totally burried under snow and they all survived.

http://data.mactechnews.de/446513.png

Yes, packed now is not the same as naturally fallen snow.
Packed snow very easily turns into ice and then you have the plant into an iceblock instead of a very fluffy structure, that lets light and air pass easily.

Cristofre, Please clear up my misunderstanding. Are the mandarin more tolerant of the cold and unprotected or are they the satsuma with the greenhouse built around them ? I have two Meyer Lemon and two Satsuma all in ground but I haven't covered them yet. I am waiting for temps below 25 for more than an hour or so but I don't want to be foolish. They are in ground and seem to be hardened off nicely. I have large Christmas lights and frost cloth ready but so far nothing below 28 for an hour or so .

I think I kept them too warm too long last year and I had a little damage. I don't want to hurt the Meyer and would really need to put frost cloth over all together. I made a mistake and put the Satsumas inside the Meyers in the row. The Meyer are on each end. I put a tunnel over the whole row and probably left the tunnel up a little to long last year. The Meyer with a little freeze damage really loaded up this year. The undamaged one had just a few. I might have them set up to off set each other if they alternately bear fruit !

Thanks, Tom

I am not Cristofre, but I can give you some advise.

You never can put too much warmth.
Just cover with foil and keep it as airtight as possible.
Heat with Incandescent light bulb, that is the best and cheapest way to heat: 95 % of the energy go to warmth and 5 % to light.

Thanks for the advice but my weather conditions are much different than your weather. We can have 80 * F weather one day and in just a few days we can have bitter cold wet weather that ruins fresh new tender growth. It happens over and over so I like the citrus hardened off and mostly dormant during winter. If we have a long cold spell followed by very warm unseasonable temps then I have to work hard to protect my trees when we have a suden change. It would take a lot of tin foil and I would need to get it off as soon as we got warm weather again.

I do like the large Christmas tree lights but they are getting very hard to find because the LED lights are much more efficient to operate for light. I do agree the old fashion bulbs are much better for warmth and I hope to always have a few on hand. A large heavy cardboard box works great too but my trees are getting too large.

To repeat to maybe be more clear. We usually have great weather all winter where I live but we do have some extremes from time to time and I don't think the foil would be reusable. My frost proof fabric with lights , black barrels and maybe even a propane heater for brief periods work great for me but I want to be smart and use as little as necessary but I do want to be safe for the citrus trees.

I am a little concerned about the Meyer cold tolerance vs. my Satsumas . From what I have read the Satsumas can take it pretty cold if they have been cold already.

Tom

Yes, meyer is not so much hardy ...

The hardest lemon is Genua/Genovese
The second hardiest Tipo Toscana/Tuscany
Third Villafranca

The Ichang lemon would be about the hardiest lemon / hybrid. None of the true lemons are hardy.

Just for a heads up, my Meyer has seen 17F with no damage to the tree, every true lemon I have tried was fried at about 28F.

Thanks Laaz, that is very encouraging. Did you agree with what I was trying to say about not bitter cold and a heat wave in the middle of winter ? Tom