I was just wondering if citrus trees need any chilling hours, i doubt this but i just wanted to know for sure.

No they don't. In the consistently hot, wet tropics, they do tend to become unsynchronized in their bearing, producing several small crops per year. But they do still bear. In climates with short days and/or a dry season and/or cold weather, any or all of those triggers can tend to synchronize the tree to a single flowering and therefore a single crop.

It is also true, though, that with no cool weather, oranges will not develop a beautiful orange peel color, tending to stay greenish. Also, blood oranges will develop little or no anthocyanin pigment, so they are not red inside. Grapefruit and some mandarins color up just fine, though, with no cool weather at all.

Do citrus ***NEED*** cold weather? Your critical word is NEED. I would almost never disagree with Dr. Manners, and expect to be right. I would REALISTICALLY say it all depends where you live. I have always read in citrus production books, that in the tropics they don't need (require) cold weather because they use the dry season to fruit. In the subtropical regions they could still use a dry season, but REALISTICALLY citrus use the colder season (CHILLING HOURS of less than 68F) to differeniate the buds to floral buds. Everything I have ever read, most common citrus require (need) 850 hours at temperatures below 68F to set a good crop, in the absents of dry season. So do citrus absolutely NEED chilling hours, Dr. Manners is correct - no. But in the USA chilling hours is how citrus do it. So Valenciaguy, move your trees to Bogota, Columbia and your trees will not NEED chilling hours, but here in the good old USA you better count on them. - Millet

Ok so i live in zone 6b in ontario so how could i create the prefect climate for my trees or would just bringing them inside the house like i was planning to do. Or should i keep them some where in the house where it stays cooler like the basement with a light?? i definatly can't leave them outside.

im in zone 6 here in Tennessee (strange how that works!)

Mine came indoors for the winter, lived near a window, got sun and a bit of supplemental light, and are just fine this year. Meyer and Meiwa lived indoors and are now flowering.

Id opt for in front of well lit (ie south) windows if you have some, and give it a try!

It might be neat to see if cooler garage vs window gives better blooming, but i dont know if the added electricity bill would be worth it...

Valenciaguy, 68F(20C) is not exactly cold! - Millet

Ya i guess it really isn't that cold i will stay with my orignal plan.

The chilling hours of citruses is quite different than the chilling hours accumulation of pomes and stone fruits.

It would only serve as correlational estimates for time of blooming, so it doesn't really mean cause and effect. In this context, the chilling hours are inducing some sort of water stress to the plant. The inactive roots while the leaves are slightly active during the coldest months, will have some stress effect, and of course this will correlate well with some measures of chilling hours. But mind you, I don't believe that it is the chilling hours that will induce the blooms, I believe it is more related to stress.

Case in point, as Millet have said, tropics will have a different kind of stress counting for inducing blooming, during the dry season, followed by wet season.

Joe I go along with your thoughts on stress. It is the dry season, the chilling hours, that cause the tree stress. In fact you see it also directly after the stress of citrus leaf drop. The tree quickly puts forth a lot of blooms. I never thought of short day length, but Dr. Manners also mentions short day length as a stress, though I would think a lesser form of stress. - MIllet

I'm not sure "stress" is exactly the right word, although I use it as does everyone else. What we really mean is something that causes the tree to completely stop growing, above ground. Something that puts the buds into complete quiescence. And short days may contribute to that.

In the equatorial tropics, where temps virtually never fall below the mid-70s, where there is little variation in day length, and where there is no defined "dry season," one has to wonder why those trees still flower and bear. I presume it is that even in a "wet" climate, there will, from time to time, be a few weeks of little or no rain, and it may be just enough to trigger the trees to flower.

I would take it the quanitiy and duration of stresss or quiescence (latin from where we get the word quite) relates in how full the bloom, thus the potential crop will be. Also, as Dr. Manners wrote above, my greenhouse Moro Blood oranges do not turn red but stay orange, due to the higher temperatures. This winter, I am moving the Blood Oranges to the far back of the greenhouse, the opposite end from the heating units, where the temperatures are lower. We'll see how this affects the coloration. - Milllet

Millet, I think it is the diurnal fluctuation that makes for deeper pigmentation. In Gene Lester's farm which has a strong maritime influence and there is not much difference between day and night temperature, the pigmentation is minimal for blood oranges. It is interesting to note also that both the variegated and regular Cara-cara doesn't seem to be affected, it still has pink pigmentation. Us here in the inland we have extreme fluctuation that even the skins of some of our blood orange become full red like red plums. So perhaps, you will think of a cheap way you to achieve greater diurnal fluctuation within your greenhouse localized for the blood oranges. Putting it far from the heater is one step. Can't think of what to do next, but you may perhaps find a way to achieve it.

Joe, the Cara Cara gets its red coloration from Lycopene which is a carotenoid, thus not affected by the difference in temperatures. The Blood Orange's coloratiion comes from anthocyanin. Anthocyanin is affected by climate. - Millet