If I want to reduce the growth of citrus trees strongly, which rootstock I should use? The Flying Dragon is one option - but how much it reduces the growth? 25%? 50%? And what about other citruses - calamondin or, well, Microcitrus australasica f.e?

In Estonia, the easiest method for dwarfing a citrus tree, is simply to grow the tree as a containerized plant. - Millet (1,091-)

Morphine do you have any reference for that? Don't want to argue, but we have FD-rooted trees 15+ years old that are not yet 6 feet tall. If they ever grow large, it likely won't be in our lifetime! I don't recall ever seeing an FD-rooted tree of any age, as much as 10 feet tall. It just doesn't happen here. And I've seen many of them, some quite old. I do consider it to be a truly dwarfing stock.

I bought a Calamondin tree that is supposedly on ultradwarfing rootstock, which I suspect is FD. Planted it in the ground, gave the best nutrients that I can find, it is 26 feet tall! The fact that it is a calamondin, which generally are small trees on their own, and I have this 26 feet tall beauty that has given me award winning wines. I no longer trust the ultradwarf labels on the citruses from any nursery.

And like Millet said, is so true that the container has more effect on the height of the tree than its rootstock. I have another Calamondin tree kept in 5-gallon container, 10 years and it is only 3 feet tall, and the rootstock is labeled as semi-dwarf.

About a couple years back, I have a mandarin grafted unto FD, planted it in the ground, gave it some nutrients, and the first year it almost did nothing, but now I have seen many juvenile sprouts shooting for the skies. This going to be a big tree afterall.

Sometimes it has to do more with your backyard soil, your climate, the care you have given, drainage, nutrients, water management, pest control and the whole shebang of rituals done personally.

Most of Florida's sandy citrus soils are inherently strongly acidic, not alkaline. In our area, 4.3 would be "normal" so we use a lot of dolomite. We are comfortably the #1 citrus-producing county in the State. On other rootstocks, our trees reach some of the largest sizes of any commercial citrus trees in the world. So I'd think FD would do very well here (it actually does; but the trees stay short). Do you know where there are 12' FD trees? And how old they are? I'm not arguing that they don't exist; but it surprises me that I've never seen anything like that. And I've visited most of the major citrus-producing areas of the world.

My experience with dwarf citrus trees grafted on flying dragon is that they grow much slower than trees on standard root stocks. After 14 years in the ground, they are only 6 - 7 feet tall, and for the ones in containers, they are even shorter yet. - Millet (1,091-)

I eagerly believe that the effect of dwarfing rootstocks is (more or less strongly) reduced growth rate. It's true also in case of apple trees and strongly depends on rootstock/variety combination. But at least for common fruit trees - apple, pear, cherry, plum - the effect is not limited with growth reduction. Dwarfing rootstocks also force trees to reach their fertile stage in younger ages and the last effect is sometimes said to be very strong also in case of seedlings. At the same time, trees on dwarfing rootstocks may reach the height of 'normal' trees (though as a rule, they do not) - if not pruned at all. The trunk diameter and crown volume remain lesser, though.
What I am actually interested in, is there a possibility to shorten the juvenile stage of citrus seedlings via using some specific rootstocks. Does someone have any information regarding this?
For merely reducing the growth, one would grow citruses in pots as Millet said. And for me it's not only the easiest way but also the sole way to grow more than a couple of citrus trees, no matter on which rootstock...
I also suspect that potted seedlings not only grow slower but they also may develop slower and therefore reach the fertile stage later.

NB! A silly question from a nonprofessional follows!
The citrus world production is nearly two times bigger than apple production and cost and labor effective technologies must be at least as desired in citrus production as in apple production. Using dwarfing rootstocks surely would be one of the effective ways to gain this purpose. But there are no "real" dwarfing citrus rootstocks as morphinelover writes - why?

Morphine -- no argument at all that FD itself can get tall. I was meaning citrus scions budded to FD. We have an FD seedling on our campus that is over 12'. But all of our budded trees are much shorter, and remain so for life.

Harriest -- There are several likely reasons for a relative lack of rootstock diversity in citrus:

1. Nucellar embryony. Historically, the industry has selected in favor of nucellar varieties, which does away with much diversity in the seedling generation. Apples, on the other hand, produce wide variation in a seedling population, from which one can select for desired characteristics, such as dwarfing. And it's a double-edged sword in citrus -- it would be nice to have monoembryonic types from which to breed a new rootstock, but because we want to produce nursery rootstock trees from seed, it's important for the final product to be nearly 100% nucellar. That's a tall order.

2. The large-scale commercial production of citrus as a grafted crop is very young, compared to apples, lagging by perhaps a couple centuries; so there has not been as much time and effort put into finding dwarfing stocks.

3. When you look for crops with extremely diverse rootstock choices, you're pretty much stuck with apples. In peaches, grapes, various nut species, and other major fruit crops, yes, there may be more rootstock diversity than in citrus, but really nothing that begins to compare to the situation with apple. So it may be that apple as a species simply has more genetic potential for such variability.

4. Someone took an interest -- apple research, particularly at East Malling, but also at other research stations around the world, have put generations of research into apple rootstock development. There are relatively few breeders of citrus rootstocks in the world, and they started the process relatively late in history.

5. Less reason to look -- "standard" size citrus trees, while much larger than we'd like, from a harvesting standpoint, are tiny, compared to the size of a mature, standard-size apple. So I'd think people throughout history would have had a greater interest in bringing down the size of apples, than they had for citrus.

6. Perhaps some bad luck -- it seems that when we find a significantly dwarfing stock, there is always something unacceptably wrong with it -- 'Rusk' citrange won't make enough seeds; 'Rangpur' x 'Troyer' hybrid is susceptible to several severe viral diseases.

Of course I can't prove that any of those are the "real" reason for the relative lack of dwarfing rootstock selections for citrus, but those are the commonly held views. And I have to wonder, now that a high percentage of rootstocks (at least in Florida) are being produced via tissue culture, might we soon see new stocks for which a low seed count or monoembryony are no longer considered detrimental?

Thanks, Malcolm, for your in depth answer! I myself had thought about two things - something very different in citrus biology (nucellar embryony!) and disease problems. The first makes real hybrids difficult to get and the other may strongly reduce usability of them. Somehow I did not think about that as citrus seedlings mostly are clones of their mother trees, a question about suitable rootstocks may easily not come to mind at all!

I planted three trees on FD(I grew and grafted the rootstock) the same time about 5 years ago, same size. The clementine and fairchild mandarin are less than 6 feet. The page mandarin is at least 10 feet tall, maybe taller, more than twice the size, and much more vigorous. They are within 10 feet of each other and last year was the first year of production for all. ?????

MrTexas -- interesting! I don't think we've tried 'Page' on FD. So I have no experience with it, although on other stocks, I don't expect 'Page' to be unusually tall or large, compared to other varieties. And I've wondered if inherently vertical varieties (think 'Ponkan') might get taller than other cvs, even on FD?

I wonder though -- do you recall your rootstock seedlings? As you may know, FD produces a high percentage of non-true-to-type seedlings. They are apparently nucellar, but mutant, much like navels are wont to do. I read a paper once (don't remember where? Maybe Proceedings of the Florida State Hort Society?) saying that you could predict performance by how curled the thorns were -- the straighter they were, the less dwarfing, and the more curly, the more dwarfing; and that only the very curly ones should be considered true FD. Is that a possibility here?

Malcolm