Trifoliate orange is suitable for use in cool climates where maximum freeze hardiness can be developed. Freeze hardy rootstocks, like trifoliate orange, acquire freeze hardiness at ONLY 70F day temperatures/50F night temperatures, whereas the less freeze hardy rootstocks do not acquire freeze hardiness until 50F day/30F night temperatures occur. Interestingly, trees on Flying Dragon rootstock have NOT been shown to be more freeze hardy than trees on other trifoliate orange types. Note also that when SEVERE FREEZE damage does occur to trees on trifoliate orange rootstock, they recover more slowly than trees on more freeze sensitive but more vigorous rootstocks like rough lemon. Trifoliate orange is satisfactory rootstock for most sweet orange cultivars, especially navel, but fruit size for grapefruit scions on trifoliate orange rootstocks may be relatively small. Trees budded on trifoliate orange produce excellent fruit with high soluble solids (sugars), good juice color and a smooth thin peel. Fruit also holds well on the tree. However, fruit, especially for the fresh market, can be small because of heavey fruit set. Therefore, some thining might be required. - Millet

Cool posting!

Remember the usuall slow growing of the stock, which appears not only in recovering grow after freeze damage, but also in normal growth habit...
Sometimes the anuall new growth of a container grown Citrus on Poncirus trifoliata can archive often only 4 to 5 inches.... on other roostock, these new grown can reach three times that new growth.

But, I fully agree!

Steve, I would expect that most people who grow citrus as a containerized tree, would count the usuall slow growing of the trifoliate stock a good benefit, not a drawback. - Millet

Actually, I have no idea what you are talking about. I have never seen a trifoliate tree, nor any other variety of citrus tree grow with a weak bent down trunk nor with willow type branches. But to be honest, there are not many citrus growers in Colorado. The two largest growers are myself and Joe. Only one of my trees uses a stick to prop up the trunk, and that tree is not on Poncirus, it is a Useless (Eustis) Limequat growing on its own roots. Too obtain strong stout trunks and strong sturdy branches is extremely easy when the tree is grown properly. There are many threads on this forum with instructions on what causes straight, firm trunks and branches, and how to accomplish this. Use the search function, and read away. There is no reason to have weak trees. Actually, I find the growth of trifoliate stock to be exactly the very opposite of what you are saying, trifoliate stock produces an abundance of fruit, and nice trees. I am currently growing 127 different varieties of citrus in my collection. Some in the ground, all of the rest are growing in Air Root Pruning-Root Maker Containers from 5-gallon to 30 gallons. I now ONLY use Root Maker brand Air Root Pruning Containers. The absolute worst container a grower can grow trees in, are the common hard sided, round, smooth sided plastic commercial nursery containers. The trees are growing on many types of under stock, but a lot of my trees are on Flying Dragon, and various varieties of Poncirus. Another stock that I like is Smooth Flat Seville (SFS). European growers should not be having any trouble with FD and Poncirus under stocks. Take care. - Millet.

Steve,

I grow and sell citrus on trifoliate rootstock. I can grow a 3' tree in s 3 gallon pot in about 12- 18 months, and many growers further South can grow them in less time that that. I have seen plenty of healthy, bearing citrus on both regular trifoliate and Flying Dragon rootstock, both in the ground and potted. I would suggest that you have a problem with you growing technique. One piece of advice I can suggest, to speed growth, is to remove all fruit until your tree reaches the desired size. You might also consider Millet's advice in regard to growing citrus in containers.

Ned

All of my 7 trees inground trees are on trifoliate stock, 2 of those on FD. It appears to me that the biggest difference in growth comes from what is grafted onto the rootstock. My Lisbon Lemon has had 4 growing seasons and is now well over 10 ft (starting from about 3 ft). The 2 satsumas that are in the 3rd growing season are barely 3 ft now, with the exception of the Daisy mandarin that I grafted on a trifoliate sprout which has grown to over 4 ft this growing season from a single bud--I can hardly imagine anything more vigorous.

The 2 that are on FD were planted last July, one of those has put on more than 2 ft of growth, the other a little over 1 ft. The advantage to me in having dwarf plants is more varieties in my limited space or being able to plant in a very small space.

My limited experience does not allow me to compare to other rootstocks, but I am satisfied with what I have gotten out of the trifoliate stocks that I have.

The type of citrus you bud to Trifoliata will make a big difference in growth rate. Budding Satsuma to Flying dragon will indeed be a very slow growing tree as both cultivars are slow to begin with. Grafting a lemon to standard Trifoliata will result in a very fast growing tree, as both the rootstock is faster than FD & Lemon is a very vigorous cultivar. Using Swingle will almost double the growth rate, but you will lose some cold hardiness.

All in all it depends on the environment the citrus is grown in as will as the rootstock & scion type. Growing citrus in containers in cold environments will indeed produce a much slower tree than if it is grown in a warm climate in the ground...

If people will go back and read some of the
older Hilgardia articles on Citrus rootstocks
or get out the books you guys have on Citrus
and go back and read the article listed in
the reference sections that in some cases
the book authors have not read themselves,
we can see what we can expect from some
of the partially deciduous Trifoliate orange
rootstocks in comparison to Sweet Orange,
Sour Orange, Citrus macrophylla, Rough
Lemon and the Citranges. Much of our
research on rootstocks have been carried
out not for root production, not for better
and more efficient nutrient uptake but
studies were extensively carried out for
added disease resistance and from the
Sinclair Grapefruit book we know that
much of our intent studies were carried
out in attempt to help along or promote
Oranges much more so than other Citrus.

Then people came along and found that
dwarfing rootstocks could slow down the
growth rate of the tree and still impart
disease and later on insect resistance as
well in the plant but people did not ask
themselves at what price for other things
such as have disease resistant rootstock
to Tristeza but then see more fungal
and/or bacterial issues in the plant later
on.

We solve one issue that can kill the plant
and spread and we overlook another issue
that can also kill a plant and spread all in
the name of being Tristeza or in some
cases Virus free. We do not take into
account that when we clean up the viral
activity that we can make the plant more
susceptible to fungal and bacterial pathogens.

Later on we learned that much of our
graft transmitted diseases from plant to
plant were not coming so much from
the infected scions but were initialized
from contaminated rootstocks and then
when we take infected wood and bud or
graft it onto an already contaminated
rootstock we can expect to have more
trouble later. Any wonder how Citrus
Canker became so widespread in some
areas? I've mentioned to a few people
before if you want to help for that disease
you have to start with growing much
cleaner (sanitary) rootstocks.

There is a reason why Trifoliate orange
rootstock do better for container plants
than they do for some of the in ground
Citrus forms and it seems that Steve
knows what some of those issues we
have with in ground plants are. All
we have to do is take a tree out of
the ground that is faltering or was hurt
by a freeze and we can see what our
real nemesis is and that is what we may
want from a dwarf tree for size and overall
shape of the tree and get but we also do
not get a whole lot for root production
and new root shoot development when
in the ground.

People do not realize that there is a price to
pay for dwarfiness and much of the time that
price comes when a juvenile tree gets hurt
by a severe freeze and we wait and wait for
new growth to help sustain the plant later on.
This is why I gave up on the dwarf form rootstocks
after the freezes of 1990-1991 in which I lost
so many of the in ground dwarf form Mandarins,
yet the semi-dwarf Mandarins and Tangerines
both in ground and other Citrus and in containers
on our blacktop driveway made it with no losses.
It was my feeling that the dwarf from rootstocks
used for those Mandarins that perished were not
nearly as cold hardy as what they were being touted.

When we pull the trees out of the ground and take
a good, hard look at the root systems we can see
where our real problem lies for the new growth
regeneration in the tree. There are rootstock
studies that were carried out by the University
of California, not necessarily were all conducted
at the Riverside Experimental Station either, that
showed that even when the rootstock could tolerate
low soil temperatures that there was a difference
in which forms of rootstocks could impart cold
resistance into the scion portion of the tree. Cold
resistance is not a whole lot more than sap movement
within the tree which in itself chemically combines
with other substances and form a anti-freeze like
chemical within the plant. If the roots are in flux
whereby they are not functioning imbibing water,
absorbing nutrients and even soluble salts and other
solutes then the anti-freeze like protection may not
be seen. Another thing that needs to be stated is
we have to be mindful of the synthetic soil medium
we are using for our container plants as we may
not get or have the microbial activity like we get
when the microbes are working around colloidal
particles.

Some people like the easily managed trees that
are easier to pick, easier to maintain and take
up less space so we can have more trees in a
given area than we can have with semi-dwarfs
or standards but with partially deciduous trees
we have to deal with in flux states whereby the
root system grows to compensate for the leaf
loss due to the tree wanting to slough off leaves
and produce more apical or lateral growth. When
the terminals stop growing so does the roots and
when we have a root system as our feet for the
plant stop growing and go dormant then what we
were told or perceived as being more cold tolerant
does not mean a blasted thing if the roots are not
capable of carrying out their normal chemical
functions. This is how I know that the 55 degrees
being absolute zero for a root system is pure BS
for in ground trees but not necessarily for a tree
grown in a greenhouse or in the home, in that we
can still see new top growth being produced by
some trees even in freezing weather but not
enough of you have seen it and were too busy
to take someone else's word for it that also has
not seen it. It is the activity of the roots is what
produces the protection and through transport
within the plant enables the top growth which
is more exposed to the cold than the roots to
help internally ward off the onset of cold injury
to the tree.

Having a rootstock be able to withstand or
impart freeze resistance to the tree has no
meaning if the root stock is not carrying out
its chemical functions. A Flying Dragon
rootstock that may be hardy down to zero
or minus degrees is useless if that same
rootstock cannot function in those same
low temperatures. We also know that the
chemical constituents of the rootstock does
enter into the scion and we also know that
bitterness in the rootstock can be transmitted
into the fruit of the host plant.

Some years we may not see the overall
effects of the rootstocks imparting its
own genetics into the scion and its fruit
and in years in which the Flying Dragon
had to ward off some real cold we can
get less sweet fruit from our Sweet Oranges
in comparison to the same Sweet Oranges
that were budded or grafted on Citrange
(semi-dwarfing) rootstocks instead.

Jim

Steve, when talking about what under stocks are used, as when you wrote above ...."in Spain..stock is Carrizo... and also ...here whole orchards are grown on Citrus volkameria.. keep in mind the difference in root stock preference between commercial culture and door yard, container culture and citrus grown in cold areas. Also under stock preferences between European and western growers. Although, a few people want huge trees and therefore use Volkameria, Swingle, and perhaps Carrizo, door yard growers much prefer smaller trees, that still produce high quality fruit. Trees that are grown on FD and other Poncirus hybrids, give them this benefit. In the USA smaller dwarf trees are now becoming quite popular among commercial growers, when planting out new groves. For both commercial growers, and home owners, a "dwarf" tree is simply one defined by convention as being about 6 to 14 feet tall. Commercial citrus growers are very interested in dwarfing rootstocks for citrus, because small tree size allows a higher tree number, or density, per acre, fewer IF ANY hedging and topping (pruning) cost., and MUCH EASIER FRUIT HARVESTING on smaller trees. A number of factors can influence tree size, but for most commercial citrus cultivars, trifoliate orange rootstock selections have been generally divided into two groups based on flower size. Trees on small flowered trifoliate orange selections like Rubidoux are typically 15 to 20% smaller than trees on large flowered selections like Pomeroy. In California, my home state, where dwarfing citrus rootstocks have been widely used, 8 to 12 year old Navel and Valencia oranges, Minneola tangelos, and Dancy tangerines on Rubidoux trifoliate orange rootstock at different sites range from 10 to 14 feet tall. Comparable trees on Pomeroy trifoliate rootstock were 15 to 19 feet tall. Standard root stocks can reach 25 to 35 feet tall, and are very hard to harvest, and difficult to manage economically. Commercial growers are now even using additional growth hormones like auxins and cytokinins to further reduce tree size and increase lateral shoot development. Steve, in my opinion, European growers need to ketch up on grove technology. After all, commercially it is all about two items. quality and economics. Regards, - Millet

Jim, as always your posting are some of the most rewarding readings on this forum, and always offer a lot of information. If I could, I would like to offer several responses to a few of your comments. You said...("after the freezes of 1990-1991 in which I lost so many of the in ground dwarf form Mandarins you gave up on using dwarf form rootstocks")...... It is known that when trifoliate orange is used as a rootstock for mandarins and mandarin hybrids, bud union incompatibility is often reported.

Also, when referring to when a root stock goes dormant....("does not mean a blasted thing if the roots are not capable of carrying out their normal chemical functions").. This is true, but this is true for all citrus root stock varieties, not just trifoliate forums.

The reference......('A Flying Dragon rootstock that may be hardy down to zero or minus degrees is useless if that same rootstock cannot function in those same low temperatures').......No citrus rootstock known can function at temperatures down to zero or minus degrees. In fact 99 percent of other rootstocks would have long ago been dead at such temperatures.

Jim, I understand what you are saying about 55F and its being BS about absolute zero for in ground citrus tree root function, However 55F, is a well founded fact, and I totally believe it. You are right to point out, that the 55F absolute zero topic is much more important to container culture, than it is to in ground trees. This is simply because in areas where citrus can be cultivated as in ground trees, the soil temperatures at two inches below the surface never comes anywhere close to 55F. In most sub-tropical areas of citrus culture, the soil temperature several inches below the surface does not often fall below 72F. Interesting conversation. Personal Regards, - Millet