........."trifoliate organge sets a winter quitness, but not a true dormancy"......This statement is true of every single variety of citrus, not just trifoliate orange, thus whatever the depth of cold hardiness obtained by a particular variety, causes each variety to bloom earlier or later

......"where superior cold hardiness is usually not requried so here there are not realy advantages, for most container growers"........ Respectfully, I submit that almost no container grower utilizes Flying Dragon or Poncirus trifoliata for their cold hardiness, but rather for its dwarfing attributes, because of the very fact that the tree is being planted in a container. Container grown plants do not need to be cold hardy, as they are moved to safety as required.

........"Sour Orange is abandoned in Spain for commercial and it's use is forbidden by law"........ Regretfully, Sour Orange has been abandoned in many areas of the world due to the variety being so very susceptible to the Tristeza virus, and that is a real shame, due to the fact that sour orange performs so highly in most every other aspect. Anyway, even with the difference of opinions, or perhaps because of the difference of opinions, this thread has been interesting, and I'm sure a helpful posting to the membership. I've enjoyed it. - Millet

Well, Millet,

in germany most growers use Poncirus trifoliata not because of dwarfing attributes and slow growth, most of them justify it's use because of it's superior cold hardiness.
And none will understand, that it's not needed, as you mentioned, because container grown trees are mobile and can be sheltered if needed.

I abandoned it's use, because of the slow growing habit. Because I have a CaraCara on Poncirus trifoliata, and in two years since I own it, the tree only made 10 inches new growth.
Can you tell me, what I should do with such a little thing? That's not a tree, not a shrub, it's nothing.. Even if I feed this to death, it won't grow...

So that's why I choose other rootstocks, because I want growing trees, no trees which act like a snail!
And if snails eat leaves and spider mites cause leafs to drop, and the plant should regrow, but doesn't exhibit the power to do, well, then I must change and get other rootstocks which do better in my cultural circumsances....

That's why I use vigorous rootstocks, like Citrus volkameriana, Citrus jambhiri and Citrus limonia.
And about dwarfing:

Poncirus trifoliata isn't a true dwarfing rootstock, it's simple slow growing... but in commericial groves it's found that with correct feeding and cultural maintainace, the trees get same size as on other slow growing rootstocks.
Poncirus trifoliata 'Flying Dragon' is dwarrfing, but as I was reported form Israel: "We talk about dwarfing, not harvesting the fruit on our knees!"
for container well, but only if you can provide a periode of cold, just to match the biological demand of the Poncirus trifoliata stock.... or you will have a plant, which is growing like mine: Slow as snails!

so I use Citrus limonia, it's very good. Not real dwarfing, but if get's rootbound, as typical in containers, the trees will stop their upright grow and tend to grow more lateral.. Very well for a container plant.

So I have seen many trees on Citrus limonia and Citrus volkameria which exhibit a strong, vigorous growth and need to be pruned often twice a year, but build up beatifull little trees...
But most of the trees on Poncirus trifoliata often in containers looked very unhappy and less vigorous.

So it's everybody's decission. If someone is lucky with his rootstocks, why he should change? There is no rule to do and no cause for this.
So do not change, do it only if necessary, or you feel other ways give better results... but in the slightest doubt, do no change....

Steve, it is alright with me, you certainly can grow your trees in Germany any way you wish. It seems that we are going around in circles, and any real assistance to the original intention of this post is being lost, so I will bow out of this thread, and let others who have new information or advice for Philip join in. Take care, and thank you for becoming a member of this forum. - Millet

Anyone want to start a debate on the anthropogenic effects of global warming?

We won't need to worry about cold tolerance since we will all be burned to a crisp within the next few years. Just for fun, what's the most heat tolerant rootstock?

Phillip

I would guess that the most heat tolerant rootstock would probably have excellent cold tolerance and drought tolerance as well. The mechanisms of tolerance for these extremities are the same or similar.