After reading many posts by a great deal of people I have seen many people refering to citrus as having to have chill hours like peaches, apples, and other decidous plants do. That is not the case. Citrus plants require 0 chill hours. If they required chill hours then they wouldn't be able to grow and fruit in the hottest parts of the world were the temperature never gets below 70 degrees or when you have a potted citrus plant growing in your house that never gets below 60 degrees. Thought I would let this be known because there are alot of people confusing citrus plants as needing a dormancy period and that is not the case.

They don't require chill hours per se the way temperate fruits do, but some varieties do need a certain amount of hours below a certain temperature range (mid sixties as I recall) to put forth their best flushes of blossoms.

Millet can detail this for you as he's got the data to hand. I'd have to go look it up again.

.....Alan.

ML, this subject has been covered on this, and other citrus forums. Unlike decidous trees, such as apples, which set their fruit buds in the fall, and these buds can be easily seen, citrus trees basically only produce buds that will develop into foliage. They never produce flower buds. How flowers come about on a citrus tree, is through a process called differentiation, which is not yet fully understood. By differentiation a foliage bud is somehow changed into a flower bud. Differentiation, is accomplished through a form of stress to the citrus tree, and occurs shortly before the tree blooms. In temperate climates, this is accomplished by the lower winter temperatures (temperatures below 68F). The more hours of low temperatures the tree is exposed to, the better bloom can be expected. In tropical countries, where low temperatures never occur, the stress needed to change the foliar buds into flower buds (differentiation) , is accomplished by the dry season. A tropical citrus tree becomes quite stressed during the dry season, and upon the return of the rainy season, if the tree has acquired enough drought stress hours, than a good bloom will occur. In commercial Lemon production drought stress is commonly used to insure that the main lemon crop harvest comes during the summer months, when lemon prices, and demand are high. Without any stress hours, a citrus tree will produce foliage. - Millet (1,442-)

The chill hours required to enable citrus to set bloom, has long been known, and has been well established through citrus research. Information on chill hour requirement, is published in books, research literature, University of Florida publications, numerous places on the Internet, and can be found on just about every citrus forum. Dr. Manners , and other members, have written on this very subject, both on this and other citrus forums . - Millet (1,441-)

ML, your welcome, and also, thank you for all your contributions to the Citrus Growers Forum. - Millet (1,441-)

Okay-
I am confused.

I was the person that mentioned citrus chilling hours and subsequently got Morphinelover going on this issue.

I am new to citrus growing and did get the impression that chilling hours were necessary for good bloom/fruiting. I got that impression from a thread on this forum in Container Citrus- Container Citrus Winter Growing Guidelines by BabyBlue 11371. Patty- you posted on this same thread.

Millet and Morphinelover now seem to be agreeing. Are you agreeing that citrus need chill hours or not? Or are you simply agreeing to disagree (which I certainly repect).

Or is this simply a matter of disagreement over the term "needing chilling hours" vs "benefiting from chilling hours"?

Kyle

ML is correct to a point, in that citrus can live a healthy life, without acquiring the needed chill hours. However, without the required number of chill hours, or drought hours, a citrus tree WILL NOT bloom, or will only produce a very weak bloom. The average number of chill hours, or drought hours, is normally 600 to 900 hours during the winter months. These hours do not need to be continuous, they can be aggregated. If the tree set a heavy crop in the previous year, than the tree will need the higher amount of hours to produce a good bloom. So the answer is YES, a citrus tree does require enough chill hours in order to differentiate its foliage buds, and change them into flower buds. Without the required chill hours, the foliage buds cannot change (differenitate) into flower buds, therefore, the tree will tend to produce only additional foliage, and not flowers, and, of course, without flowers, there will be no fruit. In Florida, every winter, the number of chill hours are recorded by the authorities, and published monthly, so that the commercial growers can get an idea of the coming seasons crop load, and so that official estimates of the Florida state citrus crop can be estimated. . I hope this clears it up for you. Take care. - Millet (1,441-)

This discussion brings to mind something I have had on my mind. My large Ambersweet had tender flower buds, just before a recent freeze, where the temperature went to between 24 and 25 degrees f. All the tender buds were killed, but the mature foliage only experience minor leaf curl. Until now I have assumed this year’s crop was lost. Is it possible that the tree will form new buds on the spring flush?

Ned

Morphinelover and Millet-
Thanks for the clarification.
Kyle