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Red Baron Peach Blossoms
Many fruit trees, such as peaches, apples, pears, and plums, have what is called a 'chilling requirement'. This means that after the tree goes dormant for the winter, it needs to accumulate a certain number of 'chill hours' before it will be ready to grow again in the spring. A chill hour is loosely defined as one hour below 45 degrees Fahrenheit. This chill requirement is important, because it helps ensure the tree won't break dormancy too early if there are just a few warm mid-winter days.

It is very important to know the chill requirements when selecting a fruit tree. My area usually receives between 600 and 700 chill hours on average, which is why I wouldn't plant Red Delicious apples (1400 chill hours) or Redglobe Peaches (850 chill hours).

If a tree doesn't receive enough chill hours, it will be slow to break dormancy, have reduced fruit set (or none at all), and the fruit quality is lower.
It's OK if the tree receives more chill hours, but at a minimum most trees need to receive their specific chill requirements to be healthy and productive.

The Texas A&M Horticulture website gives two ways to estimate the accumulated chill hours of an area, based on readily available weather data.
The first method uses the mean January temperature to chill, and the second method uses the average of the mean December and January temperatures:

January Mean Method:
Estimated Chill Accumulation = 3547-54 x (January Mean Temperature)

December/January Mean Method:
Estimated Chill Accumulation = 4280-68.8 x (December+January mean temperature/2)


However, it is important to note that these methods do not consider late cold snaps in February, like the one we had this year. I used both methods to estimate the chill hours my area received for the past 20 years, and the results are surprisingly variable. Even though my area receives and average of 600 chill hours, a Red Baron peach tree would only receive it's full chill requirement roughly 60% of the time. Much better to plant something with a chill requirement of less than 400 hours, like Midpride or Tropic Snow.

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Estimated Chill Hours for Zip Code 77379
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Map from www.sandybarnursery.com
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Tropic Snow Peaches
 


Comments

David DeShurley
03/03/2011 08:06

Hey Clayton,
Is that Red Baron Peach photo from this year? Mine hasn't broken dormency yet. Since I live in the inner loop, I'm wondering if it didn't receive enough chill hours this year.

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Clayton
03/03/2011 08:10

That photograph is from last year. Don't fear, I'm sure all the stone fruit got plenty of chill this year. Keep in mind that most of the really cold weather blew through in February, which isn't considered in the A&M formulas. I estimate we really got between 800-900 chill hours this year.

If I still had a Red Baron, I would consider grafting some other low-chill varieties onto it.

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03/03/2011 18:49

Great blog.

You've really planted some really cool things.

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stacy
03/03/2011 20:13

Clayton, do u still have the figs for me ...i can pick them up any time that u r free. stacy

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Doug
03/12/2011 21:00

I have seen websites that claim red baron peaches only need 200-300 chill hours, and I've seen others that state it's needs at more like 500-600. How do I know who is right? I'm looking for a showy peach that produces good fruit for the north Houston area, but am not interested in Saturn.

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12/30/2011 22:07

Thank you for details

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01/28/2012 11:55

good post

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Jon
08/20/2013 08:02

Hey Clayton, I found your website again this time looking to see what chill hours existed in Texas.

To get an actual accurate total, you can run a report from NOAA on past daily data... then manipulate the data using an if then statement so if temp < 45 then 1.. then sum it up and you'll get a very accurate portrayal of what the chill hours are for your area.

http://www.ncdc.noaa.gov/cdo-web/

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Jon
08/20/2013 08:49

Actually I'll partially retract that - you have to be careful because sometimes the weather station doesn't report or reports every 20-30 minutes.. you can manipulate the data to account for that then you'll have a very accurate info

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The Bell House - Growing Fruit Trees in Northwest Houston