Has anyone been successful in planting an in ground Yuzu in zone 6? I found some for sale and was planning on planting it treating it like a fig tree, wrapping it for the winter and the like.

I really doubt it. I am finding they are about as hardy as Satsuma. They have a lot more leaf drop from the cold than Satsumas do.

That would be interesting, I don't know if it would be successful or not? Figs lose their leaves and become dormant during the winter months, thus can be wrapped for protection against the cold. Yuzu is an evergreen, retaining its leaves year around. A citrus tree, Yuzu included, has only one source of energy, and that source is light. - Millet (640-)

Grafting on poncirus will make any difference? Millet you mean that citrus tree are not like the apple tree? so the tree can never go dormant?

danero, the metabolism of citrus is capable of slowing down, but citrus trees never go dormant. - Millet (640-)

Mine are on flying dragon.

I cant remember where I read it but I read that once it goes to 15 degrees it looses its leaves, although your experience says more than what I know as I have never seen an actual plant of it. I think I will try it and see what happens, I may get lucky or I may just be disappointed but at least I can try. Does anyone have any tips that might help me become more successful?

We didn't get anywhere near 15. I think the lowest we hit this past winter was 22 F. Both Yuzu lost most of their leaves, Satsumas didn't lose any...

Thanks Millet , but I was also asking if graftin yuzu (allready hardy enough) on a much hardier tree , for example Poncirus (The Flying Dragon - I heard some rumors about his instabillity ) wouldn't make the tree more cold resitant ? Poncirus can survive -5-10F , or at least the trees that I have ,they have survived in that winter to such low temps.

The most frequent mistake, when it comes to talk about citrus hardiness, is speak only about lowest temperatures. This is only 1 part of problem. Basic question is the kind of winter, how many days is frost temperature, sun/frost, frost +snow or just dry frost and many and many other things.
For example:
I put one citrumelo swimgle grafted on fl. dragon to the ground in zone 6. First winter: mild winter, only few days frost and minimum about minus 10 Celsius - no problems.
Second winter: few weeks of frost and non frost, day/night etc.. Min. temperature minus 17 celsius for a while. - frost demage on stem and bark, but after all, plant OK.
Third winter, min. temp. aprox. minus 12 celsius, but long time-several weeks day/night frost, mostly minus 10 celsius. - plant nearly totaly demaged. Citrumelo survived only 1 centimeter above graft union.
So, I took it out from the ground, to the pot. Citrumelo reborn from last buds in that centimeter of stem and now it grows together with other citrus trees in greenhouse.
btw I think, that citrumelo is much hardier, than yuzu.

Radoslav, your post is certainly correct. I believe most every one on this forum, who have been a member for some time, understands the importance of the previous climate. When a person asks what the hardiness of a citrus variety is, it is usually understood what people want to know is a temperature. A temperature, gives a person a base upon which a person can make a knowledgeable decision on what they might want to do. When the survivable temperature of a cultivar is given as a number, it is of course an average temperature, and is always understood (at least by most citrus people) that it is merely a range, and depends on what the recent, past, and future climate has been and will be. - Millet (633-)