Chill hours and hardiness and getting fruit
 

I am looking for some sort of insight as to how the number of chill hours are determined for various cultivars. For example the same cultivar from different sellers/nurseries will variously be listed as a 9 or an 8. It is the same with the needed chill hours. Usually a nursery will under state the chill hours or move the hardiness zones to the most optimistic range. What I have found is that when possible talk to an experienced grower from your hardiness zone and ask them if a particular cultivar will likely fruit. The gripe is this causes a big disappointment when after several years of waiting the tree in question will not bloom well and there is no fruit.

Re: Chill hours and hardiness and getting fruit
 

The number of chill hours in a location is roughly the following:

Between November 1 and January 1, the number of hours below 45 F minus the number of hours above 65 F.

The number of chill hours stated on a nursery tag is often calculated by an older method: just the number of hours below 45 F. To get better information on the performance of a cultivar in your location, I would contact the wholesale grower -- or at least a nursery that is in constant communication with the grower. The seminars held by Dave Wilson Nursery (wholesale grower) around the country are a good source of information.

The chill hours of a cultivar are a matter of phenotype and not preserved across generations. Preservation of phenotype is one of the main reasons we graft fruit trees instead of growing by seed. The other main reason is maturity of the fruit stock: the grafted scion will begin producing fruit the following year.

Also, if a fruit tree with a higher chill hour requirement is raised by a wholesale nursery in an area with high chill hours, then you can plant it in an area of low chill and it will bear fruit the first year (because of the previous year chill) and likely not bear fruit for all the follow-on years.

Re: Chill hours and hardiness and getting fruit
 

There are a series of questions that follow from your answer. Let us go through the first one. Let us say that the nursery has a new cultivar and that yr they had 600 hundred chill hours. Can they say that their new cultivar requires only 400 chill hrs to fruit since they only exposed the plant to one regime of 600 hrs? It seems to me the only real way to tell is to expose several different specimens of the same grafted plant to different quantities of chill hours and I suspect that aside from the USDA that few entreprises have the personel or facilities to do such a determination.
Genetype is almost always preserved by grafting. Phenotype is the expression of the genes and that could vary I suppose due different factors, but normally we expect it to be if the same grafts are placed on rootstock of the same genotype and phenotype. I have never really understood what sort of meiosis and fertilization goes on in plants and this is something I need to pursue since my training was exclusively in Zoology. Plants can do things with their cytogentics that are really strange to come up with all sorts of viable polyploid hybrids.

Re: Chill hours and hardiness and getting fruit
 

What was the question ?

Re: Chill hours and hardiness and getting fruit
 

To paraphrase, I think it was "can a nursery list chill hours as lower than the plant has been tested?"

I would say that ethically, they can't. My understanding is the lowest chill hours listed are based on growing that exact cultivar in an area with the lowest chill hours listed and having it produce fruit. I've heard comments from nursery folks, including employee's of Dave Wilson (the wholesale nursery that Richard mentioned), along the lines of "we list it as needing at least xxx chill hours, but we know it has fruiting with fewer chill hours than that." As enough reliable information is gathered, you will sometimes see a grower or nursery drop the chill hour estimate because of that new information. My sense is that most reputable nurseries err on the side of listing more chill hours than are absolutely necessary.

And I think it is agreed that chill hours are an oversimplification of the biology involved. For example, I would think it's got to matter whether the chill hours occur early in dormancy or late in dormancy.

Re: Chill hours and hardiness and getting fruit
 

So it is not just total chill hour but the temporal sequence. In my area we get middle 20's and lower that can be followed by 70's and then the lower 20's again. I wonder also if for pears for example react the same way as peaches would to temporal temperature patterns.

Re: Chill hours and hardiness and getting fruit
 

Say again --- over.

Re: Chill hours and hardiness and getting fruit
 

I say plant one and if it does not make good fruit,graft over it.

:08::woohoonaner:

Re: Chill hours and hardiness and getting fruit
 

I think that there is still alot of mystery and posibly a little balck magic and Voodoo when it comes to understanding chill hours. In my area we sometimes may get the bare minimum chil hours for fruiting, until you have to deduct the below 32 hours which don't count and then calculate the penalties for above 45 (which is quite frequently)!

I have also heard that there are different set temps for various fruits...i.e. Blueberries may have a higher or lower (I don't know) start stop temp than Pears or Peaches. Has any one else heard this?

Re: Chill hours and hardiness and getting fruit
 

I think I confused you. Any particular cultivar has a fixed chill hour requirement. It is ascertained by growing different individuals of that cultivar for a period of 7-10 years in a variety of places where the chill hours are known and then recording the successes and failures. There are a large number of proving grounds. For example out here in the west a popular proving ground for "low-chill" is the Irvine Test Station.

The point I was trying to make is that (a) suppose you have a cultivar that has a 600 chill hour requirement and it has been receiving it for at least the last 3 years at the wholesale nursery that propagated it. Now suppose (b) that during the winter (January-Feb) it is moved to a location with only 400 chill hours. The result (c) is that in the 1st year it will more than likely bear fruit, because it received enough chill in the prior November-December. Further, if it really does require 600 chill hours, it is unlikely to produce a crop in subsequent years in the 400 chill hour location.


A cultivar is a specific phenotype. Chill hours are a phenotype characteristic. Fruit stocks and rootstocks are almost universally of different phenotype.

Genotype is going to be preserved by grafting regardless. Phenotype is almost always preserved but there are some unusual exceptions; for example between perennial species that are in different genetic tribes (different Linnean families) but strangely enough are graft compatible.

Re: Chill hours and hardiness and getting fruit
 

I think you should not try too hard to understand chill hours -- they have no biological basis. There is nothing magical about 45 degrees. They were invented as a way to talk about the relative chilling needs of different plants. From what I can tell, even for a given species, experts disagree about the best way to calculate chill hours. They are a tool to use as a rough guideline. Probably if your chill hours are greater than what is supposedly needed for some plant, it'll fruit. But even if yours are lower, it may fruit.

I'd suggest you follow Sunfish's suggestion, but only plant varieties that you think are at least in the ballpark for your climate. Not much point planting something that needs >1000 chill hours if you get only 100 on average. Or better yet, ask a local expert what varieties fruit reliably in your area.

Re: Chill hours and hardiness and getting fruit
 

I agree with this, in the sense that both chill hours and degree-days (for fruit ripening) are statistical measures. I would also agree that there is nothing magical about 45 degrees. However, even those experts who disagree about chill hours will agree that the Utah method (hours below 45 minus hours above 65, 11/1 to 1/1) is a respectable measure. The problem is that almost no grower puts Utah method hours on their tags. So now the consumer is left at the mercy of the retail nursery.

Some wholesalers work hard at getting quality information about trees to their retailers, and others just focus on the volume of plants they can move through a big box store or supermarket chain. Walking into Vons supermarket this evening I saw Bing cherry trees and Washington Red apple trees for sale. Our local chill hours are 250. :(

Re: Chill hours and hardiness and getting fruit
 

All these big words guys... They're going right over my head! I mean all I do is rub two flowers together, than plant the seeds...... Hopefully get some fruit! lol

Seriously though, The large nurseries and breeders don't even have it down 100%.
I of course have to look no futher than my back feild for this to ring true.
(My) Apples; are really great examples(yes, everyone will hear of my apples sonner or later:) )they are planted widly, and have established "growing zones".
Apples that were bred to survive the harshest winters, And stated to need up to 1000 ch, actully produce(very good fruit!) and thrive with 100 ch..
As I stated to Barnetmill in a message; diease and heat talorance, throw in fruit quality in those conditions, tend to be the limiting factors for more than a few temperate fruit trees. Not chill requairment.

Its all so complex, any one solid answer would be...... (sorry cant think of a good word:( )
Not only do the genetics set the outcome of the plant, but location and situation aswell, it seems.

Re: Chill hours and hardiness and getting fruit
 

When you are pushing zones or varieties there are no experts. Just your own thoughts and research! I hope that as I experiment more and hopefully have some success I will be able to advise others in my area. Not that I will be an expert but I will have knowledge that is uncommon in my area.

Apples. Those too I am looking at acquiring. I am actually hoping to create or purchase a multi graft Apple. I was aware that the apple seems to laugh at the chill hours REQUIRED.

How is it with the seven year testing that was done the Apple fell through the cracks in the test?

Re: Chill hours and hardiness and getting fruit
 

The tags you are referring to are apparently from a wholesale grower that does not test in low-chill areas and simply uses the numbers they've been printing for decades. On the otherhand, a grower with significant business in southern CA etc. takes a far greater interest in what plants work where.

The lower chill capability of many apple cultivars has been surprising the heck out of fruit enthusiasts and some wholesale nurseries for about the last 15 years. By "low chill" I am referring to places that were previously thought to have too temperate a winter (e.g., coastal southern CA). You might want to compare numbers you are seeing on local tags with the numbers posted here: DWN: Wholesale Catalog: Apples. The numbers there are simply "hours below 45 F" and not the Utah Method. The sales staff for Dave Wilson tries to avoid using chill hour numbers at all, and instead discusses areas where the plant is known to bear fruit regularly. They do have representatives and seminars in all parts of the U.S., so check their online schedule and start finding out what they recommend.

Re: Chill hours and hardiness and getting fruit
 

Last time I checked there were no Dave Wilson people in my part of florida, but hopefully that has or will changed. If anyone knows different please let us know here.

Re: Chill hours and hardiness and getting fruit
 

Re: Chill hours and hardiness and getting fruit
 

They tour and make appearances throughout the US. There is a representative for the southeast. Contact DWN for more information.

Re: Chill hours and hardiness and getting fruit
 

Angel Oak Nurserey in Charleston SC sells their products.

Angel Oak Nursery

The DWN site says you can custom order through them.