Ok I've been reading the Albrigo work, as well as that of Southwick and Davenport. I don't think there is new stuff here -- it's been known for a long time that any "stress" that causes a cessation of growth induces flowering in citrus. Southwick and Davenport, and then Albrigo et al., tried different cool temperatures -- no one seems to have determined the exact temperature needed for a temperature stress; only that the temps they used "worked." The drought issue is better known and understood. But it looks to me like the old concept holds true -- anything that "stresses" the tree will induce flowering. And it seems to me that it has to be a new and different stress -- trees grown in consistently cool or high-altitude situations don't bloom all the time; even there, it seems to me, they need something new and different to trigger the response.

After just one more comment, then I'll leave it at that. My comment is that Albrigo's presumed chill stress temperature is given as any temperature below 68F. Dr. Albirgo also points out that besides the chill, a certian amount of hours are also required (600 and 850 hours) for "optimium" bloom, depending on the previous years crop load. I see your point that the word stress might be a replacement for chill hours. But it looks like it is the chill hours that is the agent providing the needed stress to obtain an optimum bloom. Anyway, interesting discussion. I enjoyed it. Regards - Millet (863-)

Thanks Millet, Malcolm, and David.

I hope we can pick this back up BUT can we redirect a tad. As a FUTURE non commercial grower I would like large yields but more than that I want healthy trees and I am very concerned with having cold damage to my trees especially of I try to push my zone with some. What I am interested in is any studies done that look at Cold Hardening of the tree to prepare it for freezing temps that we occasionally get. As I mentioned before are temps frequently are ridiculous having really warm days replaced by freezing temps which are rapidly replaced by warm days. I have lost Palm trees from this very thing. Citrus trees are like Palms in so much as it takes time (years) to get a mature tree. I need to be able to accurately predict the need for protection. Not that I have or will have a lot of trees, probably 15 - 20, but I have a lot of other plants that I need to protect. If I was retired it wouldn't be a problem but work continually gets in the way. LOL Not only that but every other weekend I work 23 hours in addition to my regular 40. Now I'm sure why but the local weather men here are not plant lovers as they always schedule the freezing weather when I'm working and can not get away to protect my plants.

OK let me quit rambling. Are there any studies that address this issue which primarily affects North Florida.

To get alittle back on track I found this study.
http://www.plantphysiol.org/cgi/reprint/56/4/540.pdf

Darkman, Cold hardening seems to start at about 55 F or lower. It is a time-delayed process, so the actual hardening occurs about 2-3 weeks after the cold event. Colder temperatures (down to but not including freezing) increase the amount of hardening per event, but not the speed with which it will appear. A tree may be processing several events at once. So for example, a tree with no hardiness (tender to 32 F) may experience 50 degrees on November 1, 45 degrees on November 5, and 45 degrees on November 15. We'd expect to see it start to harden, maybe hardy to 29 degrees, around November 21, then be hardy perhaps to 25 degrees on November 25, and hardy to 23 degrees on December 1. I'm making these numbers and dates up -- the exact number of days between the trigger event and the actual hardening varies a bit with variety and likely with season, and the number of degrees of hardening gained per event will also vary. But that's the pattern. It is critical that the tree be completely quiescent (dormant; in rest; not growing) when the trigger event occurs, or it doesn't work. That's thought to be the reason lemons and limes don't become hardy -- they are almost never completely quiescent.

A freeze event does two things -- assume you definitely had a freeze (say 27 F), but that your trees are fine (they were hardy to 23 F). First, it "uses up" some of the hardiness already present. We don't understand how this works -- what "IS" this "stuff" we call hardiness? In any case, the tree, hardy to 23 tonight, will only be hardy to maybe 24 or 25 tomorrow night. It has used up some of its hardiness. Secondly, and very importantly in areas that get multiple frosts -- it has lost any ability to rebuild that hardiness this winter. Gaining of further hardening is prevented until after a full growth flush has occurred.

Millet -- agreed with your last post. But cold is not needed for floral induction if there is some other "stress" such as water stress. Likely other events could also work, so long as they achieve the same level of quiescence.

Which brings me back to Darkman -- notice that while quiescence is needed for flowering, it is also prerequisite (but not the causer of) cold-hardening -- that requires some actual more severe "chill," and there is no known other stimulus that will substitute for cold, in triggering hardening.

Charles, what you may want to do is set up a microspray based cold protection system--based on what I learned when I attended a seminar at the Auburn Agricultural Experiment station in Fairhope a couple years ago. At that seminar, they laid out the economics of growing Satsumas along the Gulf Coast and the various cold protection systems. The most economical cold protection presented is a water spray system that protects the trunk and the main limbs or scaffold limbs. It will protect satsumas down to low teens. The other interesting thing I learned is how productive these trees are--about 400 pounds per tree and at a planting density of over 100 per acre, that is $20000 gross at even 50 cents per pound. Stan has some pictures of his microspray system in SC and it worked just fine last winter.

What is the average market price for satsumas?

My cold protection is covering,heating and banking. I have never tried the water spray on trunk and limbs. Morning shade can also protect citrus.


The water spray method can be very effective but be sure to supply enough water especially if it is windy and the dew point temperature is very low.

According to information put out by the University of Florida (UF), "Commercial nurseries, growers and homeowners who grow citrus north of Gainesville should use a freeze hardy rootstock such as trifoliate orange, or one of its hybrids. Trifoliate orange is suitable for use [as a rootstock] in cool climates where maximum freeze hardiness can be developed. Trifoliate orange, acquires freeze hardiness at 70F day temperatures/50F night temperatures.

NOTE: that when severe freeze damage does occur to trees growing on trifoliate orange rootstock, they recover much more slowly than trees grown on more freeze sensitive but more vigorous rootstocks. - Millet (862-)