You aren't the only one concerned. I've seen growers in the general Chicago area wondering if their trees will be shorted on chill hours given our warmer winters lately.

In my opinion, the concern over chill hours in colder areas because of the warming trend is unwarranted. Even in my Z6, there are many days of winter where the temps are below 32, which contributes nothing to chill hours. It seems likely to me that warmer winters could add chill hours to my area with less hours below 32, and more hours between 32 and 45F.

The weather extremes are much more of a concern for me. Several years of weather like we had this summer could be the end of fruit growing in the Midwest.

I agree with olpea in an area like Chicago warmer winters could be more chilling. I really can't imagine a Chicago winter in our lifetime that is short enough on chilling to cause serious issues.

Coastal RI has good chilling conditions nearly half the year, mid Oct until mid April. You get at least double what anything needs. I'd be very happy with half your total any year.

Double what you need is no better than just enough. It won't set more fruit or cause better fruit.

This post was edited by fruitnut on Sat, Jan 5, 13 at 12:56

Thank you all so much. The weather has been so strange and really from one extreme to another. It was highlighted to me by the Nor'Easter we had wrapped in a hurricane this past fall. That was one terrifying,noisy and damaging storm. I would suffer warmer winters to avoid that situation. What Olpea is saying is of great concern. No rain, just heat. Whats up? Mrs. G

"Several years of weather like we had this summer could be the end of fruit growing in the Midwest."Wow olpea,that's a scary thought! Brady

If you want to know your chill hours here are two ways to find them.

1. Buy a personal weather station and get software for it that will count the chill hours for you. Last year I found a well reviewed weather station (on Amazon.com) selling for under $100 and there is free software available. I can't tell you which one(I didn't buy one yet) but I found it by looking up software being used by personal weather stations in my area.

2. Locate a personal weather station nearest to you, and find their daily readings page and start counting. I've been doing this with one that is in a nearby canyon, at the same elevation, and their lowest readings are within one or two degrees of mine.

You can do this on www.wunderground.com . Bring up what they call their WunderMap. Check the weatherstations options and set the options to temperature. If you're zoomed in fairly close to your location (which you've already set by entering your zipcode), hopefully you'll see some personal weather stations nearby. They'll show up as small circles with the current temperature inside. Click on a circle and this should bring up a window with current information for this weather station. Find the station id in the upper left area of this window. Click on it and that will open a page(in your browser) for the current date, with a lot of data from this particular weather station. Scroll down past the graphs until you see the tabular data. In the one I watch, temperatures are updated about every 15 mins. I find the first reading at or below 45F and count the hours that this holds. When you finish the current date, up at the top of the page you can either change the date or just click on "next day".

If you don't see any weather stations on the WunderMap, zoom in a little more. The one I watch doesn't show up until I've zoomed in pretty close...although there are plenty of others visible all the time. I'm in a canyon near Los Angeles and I've been surprised to see new stations showing up occasionally as local people come online.

For Nov and Dec I've counted about 400 hours below 45F so I think I'm going to have more than the 750 I thought I might have (because a Fay Elberta peach tree fruits here), and the three coldest months are still ahead.

John

Here is a link that might be useful: sample data for 1-05-13 KCATOPAN4

Thanks John. I bought my husband a weather station for xmas. Hasn't drilled the holes for the window yet, but it will happen, he loves weather. I cannot wait to get more of an honest read. I bookmarked weather wunderground for my area, it is a very nice site. Wow, there is more to the site than I ever thought! Many thanks again, Mrs. G I am still very concerned about the conditions in the midwest.

I've been doing some research on how to calculate my chill hours so I could make this year's purchase of new fruit trees and ran into an old GW post on how to estimate based off the average temperature. I did it for every month so I could see what the estimated chill hours were for 2011.

The formula is 100*(18.5C-monthly avg).
1. Look up your local avg temperature by month or calculate it with max/min data (max+min/2). I found this link with the data I needed http://www.ocalmanac.com/Weather/we02.htm
2. Convert the data in Fahrenheit to Celsius
3. Plug it into the formula and that should be your estimated chill hours

For example:
1. the coldest month in 2011 was Jan with a max of 65.0, min of 43.0 and avg of 54.0
2. Convert 54.0F to C = 12.2
3. Plug into formula =100*(18.5-12.2) = 630

Of course this is only an estimate but I found it very useful when trying to figure out which fruit trees might do well in my area. My question to the experts is can you add up all the estimated chill hours for the winter period to figure out what would do well in your area? By my calculations Jan had 630 hrs, Feb 570, and March had 500. Can you add them all up and say that I get over 1,700 chill hours for Dana Point? I'm not sure that sound right. I would love to understand better how these things work...

Sandra

Sandra:

Your numbers are way too high. The maximum you can accumulate in a 30 day month is 720, 24x30. At the temperatures of your example you won't be anywhere near that. I have seen a model based on coldest month temperatures that predicted yearly totals. 630 might be a reasonable yearly estimate, not monthly.

There are several models that you can use. The link below should get you started. There is also a site that you should be able to find somewhere on the link below that gives running, real-time, totals for many locations in CA.

The most accurate model is the dynamic model. But it is based on hourly temperatures and requires a computer model to calculate. Hours below 45F or the Utah model are adequate for home growers.

Here is a link that might be useful: chill models

Mrs G,

You got plenty of chill last year in coastal RI. I picked two wunderground stations on the coast and they both reported more than enough chill for any fruit tree.

KRILITTL4 2011:
below 45 chill hours: 1813
45 to 32 chill hours: 1352
utah chill hours: 1612

KRINEWPO4 2011:
below 45 chill hours: 1353
45 to 32 chill hours: 1046
utah chill hours: 1394

Sandra,

Dana Point is on the coast in Southern California. You will be lucky to get 100 chill hours on a really cold year. I checked all four wunderground stations in Dana Point. Three are reporting 0 chill hours to date and the fourth is reporting 1 chill hour.

Tom

Sandra:

I see that the link above gives current and historical chill hour accumulations for many locations in CA. Chose the one that has temperatures most like your location and you will have a good estimate.

My question would be what numbers are we seeing attached to the varieties we buy, hours below 45F or Utah. I think the answer is most likely hrs below 45F because it is the oldest. But nurseries could do a better job telling us what model they are using.

Fruitnut/Tom,

That's certainly disappointing. I guess the closest location listed would be Irvine which is about 30 minutes away and lists 73 hrs. However, I got good fruit production in 2010 with 300 to 350 chill hr requirements (peach, plums and some apples) but less in 2011 (we had a warmer winter last year). So, this is still a mystery to me. :(

The nurseries are not much help either. It seems all they care about is to make a sale. Some sites will list lower chill hr requirements than Dave Wilson (I'm looking at the Zaiger hybrids - pluots and apriums). In fact, I just bought the Flavor Grenade pluot at Armstrong and it had 2 DW tags, one listing 200-300 hrs and another at 400 hrs -- on the same tree and for the same product.

Btw, if chill hrs are accumulated for hrs below 45 degrees, how can we have zero for this year so far? We have definitely had very low temps this season ...

In any case, thanks for the data and clarification.

Sandra

Sandra:

Chill hour requirements aren't set in stone. Especially in a climate like yours the only way to tell for sure is to try. Usually one can get away with higher chilling material than the numbers would indicate.

To be fair to the nurseries many factors come into play. They have to list a higher number to limit liability. As they gain experience the number usually comes down, hence more than one estimate. And these low chilling plants that we are talking about are pretty adaptable. There isn't a hard number and certainly not an easily determined number that fits all situations. The timing and quality of the chilling has an effect. Those factors vary widely by location and year. There just isn't a yes or no answer, but many shades of gray.

Fruitnut,

Unfortunately you are right. That's why a forum like this is so vital for information sharing and I hope to be doing a lot more of it this season.

Thanks for addressing my questions.

Sandra

My chill hours are around 300 mark as of yesterday this for peaches, in your state may be different crop like Apples.
What every USDA recognize as crop needing chill hours.
This good winter read on chill hours and plants. http://informedfarmers.com/do-you-know-your-chill-hours/

Here is a link that might be useful: Chill hours

Looking at the weather models out the next 2 weeks, should rack up plenty of chilling hours in S TX west to the California coast ...

{{gwi:55289}}

Sandra,

Actually if you are a few miles inland you might be getting more like 200-300 chill hours a year. KCADANAP2 is a mile or two inland and at 171 chill hours. KCADANAP5 is right on the coast will probably not reach 100 chill hours most years.

KCADANAP2 2012:
below 45 chill hours: 171

KCADANAP5 2012:
below 45 chill hours: 5

The amount of chill hours can be drastically different within a few miles in Southern California. It is the reason why I put a weather station in my backyard.

Tom

Hi Tom,

I looked up in wunderground.com and I'm actually closer to KCADANAP4. However, I couldn't find where the chill hours were. Would you mind telling me where to look that up? In any case, I guess I'll be shopping for a weather station for my little orchard. :)

Thanks!

Sandra

Sandra,
I looked yours up.Is it the one near City Hall?The KCADANAP4 is the same anyway.
To get there,I typed in Dana Point when at wunderground.Then scrolled down to weather stations and clicked on City Hall,Dana Point and it brings up History for KCADANAP4.There are daily,weekly,monthly,yearly and custom headings to choose from.For some reason though,for me,it only showed for the month of December,the 19th-31st,not the 1st-18th. Brady

This post was edited by Bradybb on Thu, Jan 10, 13 at 22:20

Sandra,

There aren't any chill calculations performed on wunderground. There is just raw historical data for each station.

I made a script, for my own wunderground weather station, to calculate chill based on historical data. It will work for any wunderground station.

There is missing data for KCADANAP4 so it is not possible to determine how much chill that station has recorded. KCADANAP2 is the next closest one reporting enough data to do a calculation.

Tom

Brady/Tom,

Thanks for the clarification. It figures that it would not be that easy. :) Like I said, I'll be shopping for a weather tracker with free software so I'll know what's going on in the orchard.

You guys rock!

Sandra

Frank-Tank! You always have the best maps. I tried to navigate your complicated weather map site. It was like trying to learn to knit over the phone! Too complicated for me. But every so often it would be great if you would post a map a month for us to see what is going on, on a larger scale. Many thanks to you and everyone. Mrs. G