the truth about chilling hours?

I have 31 trees, some citrus, some orchard fruit.
Last year we had no fruit, because all the blooms rained off.
This year hasn't been as wet, so I'm keeping my fingers crossed for the coming months!
I read about chilling hours, and I am checking websites for the chilling hours in my region.
BUT... All the information about how to count chilling hours is so confusing. Some sources say all hours below 45 and above 32 degrees Farenheit count. Others say the hours early in winter count as double, the hours late in winter as half. Again, others say for each hour above 60 in the day, we substract chilling time.
I don't know what to believe anymore. Or, maybe the chillfactor isn't that reliable or important after all?
Please share your opinions with me, it will be greatly appreciated!
Christie

Like you I have no idea how they arrive at this info. It is some sort of average and I do know that gathering info for one year is not useful. Try calling you county extension agent. Or a local nursery that sells fruit trees. Wish I could help more!

Contact your county extension office:
http://cemarin.ucdavis.edu/
They should be able to tell what the average chill hours for your area are. Also look for the chill hour requirements for the varieties you've bought. The recommendations here are to stick to varieties that require about 100 fewer chill hours to assure that fruit sets.

Another good source of information is Sunset's Western Garden Book.

This message was edited Jan 10, 2007 1:09 AM

Interesting topic. Over in the Southwest Forum I brought this very topic up. Several years ago I moved to a new house and wanted to plant fruit trees you normanlly don't find in Tucson. I tried looking up the information and like you it might as well have been written in greek. Plus in Tucson its pretty typical to have most days above 60 degrees in the winter yet the nights will be below 45. So how do I count these hours? Then I decided I was going to start keeping track for myself how many hours we get below 45 degrees. A couple weeks back I hit my 1 year total and it was 846 hours below 45. This shocked me. I have also found that the experts know about this topic as much as we do. Not very much. Even they have a hard time explaining it. I think the thing that helps more than anything is forums like this where people in the same area can share what works in there garden. Much better source for my money.

Here is a link that takes you to a list with counted recorded chilling hours so far.
http://fruitsandnuts.ucdavis.edu/chillcalc/index.cfm

We had about 500 here, but since I am still not sure if counting is enough, who knows!

Christie

Chilling hours... I'm in the 300-650-hour area, north Florida. I have been considering trying currants and filberts here but they are supposed to need 800 or more -- not a good bet, though I might buy a few as an experiment. Lingonberries can produce several crops a year, so perhaps they can get by without chilling despite their northern origins, also worth a shot. I have a huge sprawling "Leontine Gervais" rosebush planted next to the south side of my doublewide; it's supposed to bloom once a year, but after six years or so I haven't seen a single blossom; perhaps it needs chilling hours, or at least to be away from this poorly-insulated trailer that leaks heat and provides a south wall. Repeat-blooming roses don't have this problem.

Some Northern growers don't know much about chilling requirements, especially if they've sold mostly to locals and now sell on-line as well: it simply hasn't been a problem for them.

In looking for information on currants and such, I've found tables showing that figs and olives need a little chill too, as well as the fuzzy kiwi. The fruits and nuts grown commercially here, such as pecans, blight-immune chestnuts, and southern blueberries all need less chill than I get. Everbearing raspberries have been grown commercially in North Florida: one mows down the canes every winter, so that there is no early crop dependent on chilling hours; the autumn crop is all on new canes.

Due to the warm snaps usual here throughout the winter, plants or particular varieties that break dormancy late are very useful: late frosts can kill early blossoms. Pecans qualify, as do a few types of almond (it may be too humid here for almonds to thrive -- I haven't tried them yet). Some of the Scottish varieties of blackcurrant have blossoms that can tolerate freezes, but I suspect that they need more chilling than I can provide here: again, I might experiment a little if I can get plants cheaply. Sometimes I seem to have the worst of the subtropics combined with the worst of the temperate zones: too cold for the more interesting citrus, too warm for a lot of temparate fruits...