http://www.telegraph.co.uk/gardening/main.jhtml?xml=/gardening/2007/08/17/garden-citrus-orangery117.xml

Hope that URL isn't too long!

Thank you Susan, the article was interesting. I would say that the "How To Grow" section of the article was dreadful information, and will get a lot of trees in trouble. However, all in all the article was enjoyable. Take care. - Millet

Millet,
I know Mrs. Patrica Oliver personally. She knows what's she's talking about, because she takes care for a lot of the orangeries, especially citrus trees of the imperial collection in Great Brittan.
With her citrus nursery 'Global Oranges Groves UK' she leads a very valueable source for citrus and is a very famous and often cited autor in UK....

So I think the "How to grow" Inforamtions are very shortened, by the newspaper.
If you like, I seek if I can find her book anywhere and post closer informations...

I personally can also not realy fully agree with her, but as I talked to her and we got hours on telephon, I found, realy: Betwen written informations in books, magazines or newpapers and the knowledge of someone personally is space, often large as grand canyon!

Amongst the contradictory things mentioned in the article is that citruses grows when temperature is 7 to 10 deg C, which is 45 to 50 deg F. Quite very narrow and very cold for citrus growth. Most experiences of my friends here, including reading of scientific publications suggests or recommend that soil temperature should be greater than 50 deg F to have some growth, with greater than 55 deg F that is most favorable starting point for growth for more than 90% of the cultivars. The maximum upper limit to produce good quality fruits would be at 95 deg F air temperature. Ideal air temps would be between 80 to 90 deg F, and this is about 27 to 32 deg Centigrade, obviously hotter, if not a lot warmer than the 7 to 10 deg C mentioned!

Regularly clipping the tree into perfect round shape will surely limit fruit production to near zero. Heading off at the top to control height do not limit fruit production, but nipping terminal buds around your canopy will surely do. People here who uses citruses in their landscape for topiaries or hedges that are regularly clipped have never produced fruits, a character of citrus that they like.

I could only summarize the possibility that she must be growing a dramatically different cultivar of citrus... or perhaps there are other tremendous details and caveatus not mentioned in the article that could explain why the contradictory practices seem to produce very good yields while at the same time maintain nicely shaped topiary style canopies of citruses.

In cases when you plant your citruses inground, outside of the "conservatories", and you have freezing winters, specifically those in USDA zone 9 type of winter, it is strongly recommended that your citruses remain dormant the entire winter. It hardens them a lot to withstand temperatures far lower than their published susceptibility level, and could come out unscathed after the cold winters. Case in point is that I have citruses that are supposed to be cold hardy only down to 30 deg F, and if you check various websites, there are plenty, and amongst them are limes, lemons. But my lemons, have regularly survived several nights of about temperatures of 24 deg F each winter, and even survived the 20 deg F prolonged arctic freezes.

Well the trick is called dormancy. Several months before winter, we withheld anything that would encourage growth spurt. And in our area, the slowly cooling of the nights acclimatizes the citruses and bring them into dormancy, and come subsequent freezing nights, they can withstand much colder temperature than expected.

If during late winter when the weather warms up, or even in the late fall when there is still some growth, the sudden or dramatic cooling of temperature to just near freezing (but with frosts) could even nip my cold hardy citruses, simply because they still have tender shoots, and they have not gone into dormancy.

Global Orange Groves is a big supplier of expensive citrus trees here in the UK. However, they do not propagate their own stock, but import almost exclusively from Spain. This means their plants are not growing on rootstocks selected for our conditions, but for the light soils and warm conditions of Spain. If you can afford the heating costs of replicating these conditions in England, then I am sure they will thrive, but they are certainly not suitable for trying to grow outside all year.
Citrus, as US growers know, will survive and re-grow after some frost. But they surely die if first frosted in September or October, and then have another six months of cool wet soggy conditions as happens here. They simply don't get warm enough for a new growth flush before the roots rot away.
Apart from the very warmest outdoors micro-climates, there are two ways of growing citrus here. First, you spend a fortune on heating costs and keep above 55F all year. Or, like I do, you keep frost-free, allow to warm up enough in March to have vigorous growth and then put all plants outside at the end of April. Once kicked into growth in the greenhouse, they seem to keep going in the cooler outside conditions. Mid-September they go back inside.
One interesting point about heating is often overlooked. If you are already heating a large greenhouse, it costs no more at all to heat a small interior section to much higher temperatures. I have a small plastic 'tent' for my tenderest plants heated to around 70F. Any heat lost just passes out to the rest of the greenhouse and reduces the heating required there!

Dear Citrange,
GOG UK has the most plants on Citrange stocks, so the rootstock is far more cold hardy, as the most varieties GOG UK offers.
So there is not real deal for outside all year culture, because most of GB is to cold for the typical scion varieties.
And in most conservatories those plant will do well, even in most orangeries.
Usually from my viewpoint: Storing the trees in winter in an orangerie and permit a temperature around 41° F will work well for the most plants, so heating is here often not the point, and most trees will surely survive the winter time, by a temperature forced standstill of the biological activity of the most citrus plants.

so the rootstock will fit, about price and information represented in the article one can discuse.
But expecting a rootstock might have the ability to make any scion surviveable in GB... wewll, a dream and would you find one, sell it to be millionaire!
Well, just kidding.... but the rootstock isn't to blame, also the practics of GOG UK with importing citrus trees to GB isn't that worse...