The 'low chill' controversy

Axel(12b/Sunset H2)January 12, 2009

Has anyone clearly observed what symptoms appear as a result of low chill? I've read multiple reports on this, but I've never had the opportunity to observe for myself.

What I've heard so far is:

1) Delayed blooming

- I think applenut has reported that some of his so-called high chill apples simply bloom a lot later and therefore fruit a lot later, which doesn't seem to be a big problem.

2) Reduced blooming, or blooming over a longer period of time.

- I've heard about this showing up on cherry trees, leaves come out first, and blooms follow, but less and over a longer period of time.

3) Significant reduction in vigor

- One of our local CRFG members lives right on the coast and he has observed that a number of higher chill apple trees will grow much less vigorously on the Winter sunny side of the tree (south side).

i don't think this chill thing is really well understood. For one, I've noticed that a rather large number of so-called low chill apples and even low chill cherries happen to be self-fertile and early bearing. Pettingill, beverly Hills and Gordon are apple trees that come to mind, and lapins and Stella are a couple more. Are these really "low chill" or are they just self-fertile.

Now there are real low chill fruit trees: Anna and Dorsett Golden apples are not self pollinating, but they will produce up to three crops a year in mild climates and seem oblivious to the seasons. The new Royal Lee and Mini lee cherries from Zeigers will bloom and fruit when spurred by manual defoliation after a zero-chiil Socal Winter.

Now I happen to be in a medium chill area, (800h on average) but fairly freeze free. My first attempt at growing Dorsett Golden doesn't suggest it's capable of doing three crops here. it's bare right now, although it seems to be getting ready to bloom.

My basic understanding of chill is that the higher chill requirements simply keep a tree dormant through occasional Winter warm spells, or by requiring a longer early Springtime chill exposure. If it's below freezing, apples don't accumulate any chill. So most of the chill accumulated in Northern latitiudes takes place either during the late Fall or early Spring.

So the questions I have are:

- How often does it turn out that chill accumulation is erroneously attributed to poor fruiting when in reality the issue is either pollination or fruit tree maturity?

- How many "chill ratings" do nurseries pull out of thin air simply by looking at where a fruit originates from? The typical erroneous logic goes something like this: "German, Canadian and Upper-Midwest originating apples must be high chill because they come from places that have high chill."

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miketrees(WA Australia)

Axel, what a great thread starter.
I have noticed over the years that chill is not the only thing that causes the symptoms you mentioned.
Poor nutrition and post harvest stress will make a tree look like it is lacking winter chill.
I think that deciduous trees need to build up nutrients in the wood behind the buds, before the buds will burst properly.
I am not saying chill is not important, I am saying you can do a lot of things to enhance cropping in areas where chill is lacking.
I have read a paper on growing stonefruit in marginal chill areas, while they recommend using dormancy breaking chemicals, they also recommend preconditioning your trees with KNO3 sprays.
I think part of the benefit of the KNO3 spray is the build up of nutrients in the wood.
I had used urea sprays to defoliate plum trees in order to reduce disease carry over on the leaves.
While I found it nearly impossible to defoliate the trees with urea, I did find that the next years blossom on those trees was advanced and very compact (just like they had had 100 hours more chill than the untreated trees.)
A friend of mine is a mad collector of books specially anything horticultural.
He had found a book published in 1904 and it had the results of a trial using NaNO3 sprays in autumn on an ancient apple variety and the results were the same, tighter blossom and much bigger crop.

My advice if you are borderline for winter chill is to post harvest irrigate , enough to stop water stress but not enough to send your trees into a growth spurt.
Make sure the tree has enough nutrients to look deep green, but not enough to start shoots growing (KNO3 is good for that)
Make sure the tree has all the nutrients and trace elements it requires (no deficiencies)
Do some late nutrient sprays, so the leaves can absorb some nutrients and store them in the wood behind the buds.
Defoliate the tree with ZnSO4 (choosing the right time is the hard part )

I must have a hunt round and see if I can find the name of the study and the author and let you find it

    Bookmark   January 12, 2009 at 4:51AM
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sautesmom

I think you have to separate it out into fruits--you are mixing apples and cherries. There IS a controversy about low-chill apples.
I haven't heard anyone argue it about cherries, or other stone fruits.
SO are you asking about apples, or cherries, or what in particular?

Carla in Sac

    Bookmark   January 12, 2009 at 12:59PM
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Axel(12b/Sunset H2)

Mike, the KNO3 is a good idea. I don't have an issue with trees going dormant, they loose their leaves on their own, except when the trees get planted the first year. But still, I've heard it's very important to feed post harvest, and in low chill areas, unless you use the right feed, they might go into growth spurts. Basically, the next year blooms develop before the tree goes dormant. One big mistake California gardeners make is to let the drought stress cause the tree to go dormant. That's really bad and will screw up the tree's internal clock. As a case in point, I have a raisin tree that lost irrigation in August. By mid September, it defoliated. It got hooked up again, and then went into full growth mode in late Fall. It's now totally green, foliated and going gangbusters as if it is Summer.

Carla, the controversy exists with all fruits, not just apples. Often people mis-interpret poor cherry bearing on low chill when in fact it's due to lack of maturity, poor pollination, or Summer drought. But you are right in that each fruit is different in it's behavior. For example, apricots need their chill early in the season, and do best when we get the coldest weather in December. Cherries need their chill mid-Winter, and apples do best with late Winter chill.

    Bookmark   January 12, 2009 at 1:57PM
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miketrees(WA Australia)

I think sometimes cherries suffer more from post harvest neglect, since they crop so early, there is a lot of season to neglect them in

    Bookmark   January 13, 2009 at 4:13AM
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calistoga_al

My experience with fruit trees receiving less chill than required is the bloom is erratic over a long period, rather than the whole tree bursting into bloom at once. Very little fruit is set. Al

    Bookmark   January 13, 2009 at 9:04AM
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applenut_gw

Compactness of the bloom period is how I determine if an apple is "low chill" or not. Northern Spy has a very compact period here and sets good crops (too bad the quality is absolutely hideous in the heat). Nittany delays blooming until almost August but then has a compact period, so I would call that low-chill also.

On the other hand, Hawaii blooms over a 4-month period, but has a very good fruit set on those blossoms. This would drive a commercial grower nuts, but is quite convenient for the home grower. I would call this inadequate chill, but is no reason not to grow it. I've never had any trees die from lack of chill (borers usually get them first). Trees do seem to lack the vigor of colder climates, but that may be because I stuff them so close together.

My Rainier cherry literally explodes in blossoms, but only sets one or two cherries. Haven't quite figured that one out yet.

Applenut

    Bookmark   January 14, 2009 at 12:39AM
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Axel(12b/Sunset H2)

Well, I guess the topic I brought up is quite relevant as we're having a major mid-Winter heatwave. Looks like I will get to see first hand what happens when there isn't enough chill.

This year will be the least chill we've gotten that I can remember. Right now daytime temps are in the upper 70's with lows in the upper 50's as a result of a freak mid-Winter heatwave, and there is no end in sight for the warmth and dry spell. Normally we are in the low 50's during the day and the 30's to low 40's at night. We even hit the low 80's yesterday.

While there is finally a hint of rain in the extended forecast, it looks to be of the warm subtropical type. So the window for chill accumulation is quickly closing. Most years we get about 800 hours, this year, we're lucky if we hit the 400 mark.

    Bookmark   January 15, 2009 at 9:17PM
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calistoga_al

applenut
A Rainier cherry with a good bloom and only one or two fruits says 'pollination problem'. Usually it means a suitable pollinizer is not near by. Sometimes it is too cool for bee activity, but you would get more than you are. When I had your problem I bought a Black Tartarian from a nursery in a five gallon container already in bloom and put it under my Royal Ann, also in bloom. That year I had a bumper crop of cherries. Sinse I planted the Black Tartarian close by I have regular crops of both cherries. Al

    Bookmark   January 16, 2009 at 9:09AM
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applenut_gw

Well, I guess I should get my cherries straight. What I thought was Ranier is actually Royal Ann, and Lapins and Royal Ann explode in blossoms, but give meager fruit.

Last year we planted Royal Lee and Minnie Royal, which are proven producers in low chill climates, so we'll see if that helps any.

It was 87 here this week and we sleep with the windows open. I'm not worried a bit about it (the apples will fruit fine) just as I wasn't worried about the freeze in 2007 that wiped out so much citrus and avocados here. Apples are like the perfect fruit to grow in our climate, as you get something every time.

Applenut

    Bookmark   January 17, 2009 at 12:16AM
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Axel(12b/Sunset H2)

Applenut, cherry trees need to reach a certain level of maturity before they will readily set fruit. As long as they are blossoming all at the same time, then you should be all set, just wait for the trees to mature.

The trigger for fruiting depends on the rootstock. Colt and mazzard, although semi-dwarf still require the tree to be fairly mature to set fruit. The Gisela series rootstocks cause earlier fruiting than mazzard or colt. The best rootstock that causes the earliest fruiting on most varieties is supposed to be the zee interstem on citation rootstocks. They are very dwarfing and will trigger the tree into fruiting much earlier. Of course you can always girdle.

Nowadays, there are new releases that are bred for precociousness and will bear earlier, even on mazzard or colt. For example, Royal Rainier will bear even as a small tree on either colt or mazzard. Mine fruited literally the first year I planted them and they have gone non-stop since. Ironically, royal rainier has a longer more spread out bloom cycle than bing, lapins, tartarian etc... making it appear to require more chill.

Last year, I planted royal lee and mini-lee for the years when it's abnormally warm, such as this year, we're enjoying Summer temperatures here. I have them on mazzard and on the new zee interstem.

One note, we've clocked 470 hours of chill so far according to UC Davis, and we stopped accumulating about a week ago. So far, there are some interesting surprises as to what is coming out of dormancy as a result of mid 70's day, mid 50's nights, suggesting enough chill has accumulated for those varieties. What I recall I saw today was Calville Rouge and pink pearl, I'll have to take another look tomorrow. Of course, dorset Golden and Anna are already in bloom. Mini Lee and Royal lee have the largest buds and look like they might come out of dormancy the earliest.

    Bookmark   January 18, 2009 at 1:31AM
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applenut_gw

axel:

Well, we're at 167 chill hours and none in sight. Big Bear Lake is only 40 miles from me and is at 1,444 chill hours, and so is a good reference for me to check the difference on how apples perform under different chilling conditions.

Applenut

    Bookmark   January 18, 2009 at 11:15AM
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softmentor(z9/sunset13 CA desert)

you mention that you have 800 hours of chill. That is medium? that seems like enough for pretty much anything. I would consider medium chill area about 300 to 400 hours. We are "lucky" (the tropical growers would say un-lucky), if we get 100 hours, that is low chill for sure.
another symptom in stone fruit is "tippy" growth. The new growth is only at the tip of the branches instead of a good full flush.
also low fruit set. just don't get much.
I have tried all sorts of things to get more production in the face of low chill. The only thing that seems to make any real difference is manually striping all the leaves as soon as the main leaf drop has happened. Helps a little little little bit.
also growing cover crop or mulching to keep soil temp lower. Can't say that it really helps but it does look pretty and builds the soil.

    Bookmark   January 18, 2009 at 8:05PM
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Axel(12b/Sunset H2)

Not sure what is medium or high, I think medium chill is a range from 400 to 800, low chill is below 400, high chill is above 800. When all of my cherry cultivars go into full production, then I will be convinced that 800 is high chill. :) They are still young, so they have a ways to go.

We do vary from year to year. Here are the values for the last few years, total accumulation from Nov 1 through Feb 28:

2007/2008 816 hours
2006/2007 810 hours
2005/2006 976 hours
2004/2005 543 hours
2003/2004 669 hours
2002/2003 412 hours

So we are medium/high I would say, and borderline low chill on some odd years.

    Bookmark   January 19, 2009 at 12:21AM
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applenut_gw

We've found stonefruit is much more picky about chilling hours, and if you don't plant the right varieties you get squat in a low-chill climate.

Fortunately there are at least a dozen low-chill peach, nectarine, and apricot varieties that do well at 300 hours and set insane crops each year. The quality of these are outstanding also, so we don't feel left out at all. Dave Wilson Nursery has a page by Tom Spellman that lists his favorite pics.

Applenut

    Bookmark   January 19, 2009 at 6:02PM
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Socal2warm

This is a fascinating topic, as I am particularly interested in growing fruiting cherries and ornamental cherries, and live in a warm climate without any chill.

I might be completely wrong here... but one thought that I had, one of the big reasons lack of chill hours could affect the fruit yields may have to do with pollination. As we all know, without sufficient chill hours the tree does not have a clear signal when to flower, so it flowers erratically throughout the year. But there is a reason why the fruit trees are designed to flower so vigorously within a short timespan. With so many blossoms on all the trees at the same time, there is a much greater chance of cross pollination. Also a tree with many blossoms is more likely to attract pollinating bees than a tree with only a few.

So if this theory has validity, it may be possible to counteract a lack of chilling hours by ensuring ideal pollination conditions. This theory might also explain why some of the anecdotal observations by members in this forum seem to suggest that the chilling requirement is not quite as important for obtaining fruit from self-pollinating varieties.

    Bookmark   December 4, 2014 at 5:18PM
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drew51 SE MI Z5b/6a

If I didn't get chill I would just grow tropical fruit. So many are awesome, not sure I would bother with the other stuff. But as it happens I get about 1600 chill hours here.
My problem is trying to grow low chill cultivars here. Not the best idea, but I have nothing better to do. I'm only trying it with blueberries because they are triggered to come out of dormancy by temperatures, so as long as I can keep the plants cool till the weather is favorable, I should be able to grow low chill blueberries. Also I have them in pots, so if danger of frost happens during bloom, I can move them out of the frost. If I can keep them alive during the winter is another challenge. I'm keeping them in an unheated garage, out of the drying wind, temps rarely go below freezing in there, and I can heat it if needed.

    Bookmark   December 5, 2014 at 8:23AM
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Socal2warm

I have read some unpublished research that a 200ppm solution of gibberellic acid, sprayed onto the leaves or bark, of a 6 week old flowering cherry seedling can bring it out of dormancy. The gibberellic acid has to be continually reapplied, and should not exceed this concentration (otherwise the plant may stay in dormancy, strangely). The effect is noticeable after 48 hours, the buds start to open.
There has also been research on using giberellic acid to get cherry seeds to germinate without cold stratification, so this may not be surprising.

    Bookmark   December 8, 2014 at 3:27PM
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drew51 SE MI Z5b/6a

Speaking of cherries and chill I heard the CA crop, or lack of a crop. That it was a terrible year for them. I can relate 2 years ago here we lost almost all of our state's crop due to late freezes. Thank goodness they are very rare here.
This was a good year for us.

    Bookmark   December 8, 2014 at 4:15PM
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Socal2warm

Update:
Well, I have applied the gibberellic acid, and can inform you of the results of the experiment. It has been 1 week.

I repeatedly applied a 200ppm solution onto the bark, especially onto the bud areas. After 4 days, there was definitely some discernible effect, but it is very small. Several of the buds have turned slightly green. Not really obvious, but noticeable on close inspection. A small number of the buds look like they have grown just a little. But after 4 days the effects seemed to stop, and the buds did not become any greener or grow any bigger.

Another factor here, after those first 4 days there were 2 cold nights. Some of the dew on the grass had partially frozen into little ice crystals, so that might have had something to do with the stop in growth.

    Bookmark   January 5, 2015 at 3:59PM
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Socal2warm

2nd update:
It has now been two weeks
There are additional buds that are breaking and turning green.

The Yoshino had already made four little blossoms in early December, before I started the experiment. These withered away and left 2 very small red-colored leaflets, which mostly just stayed there without changing until I began applying the gibberellic acid several weeks later. The original leaflets have now increased in size a little, and the plant has sprouted two other tiny leaflets at two more locations, these ones more green. I think this particular plant had not completely entered into dormancy when the experiment started.

The other two Kanzan cherries were definitely fully dormant. Now, after two weeks, there are additional buds beginning to turn green on both cherries. One of the buds which was had been noticeably become greener during the first week is now even more green. Still, it does not seem like any of the buds have really grown. Maybe just a tiny bit, but not really noticeable to me. But the Kanzan plants are very small, less than 2ft high, very skinny, and they had been completely inactive for several months since I got them, so I think I am just lucky they are showing any signs of life.

The gibberellic acid has had the most pronounced effect on the Bing cherry, which is much bigger and already had leaves when I bought it. Many buds have turned green and have continued to grow in size over the two weeks. A few of the buds look ready to sprout or blossom. I think it was easier to get growth on this plant because it was more established and was not in dormancy when the experiment started.

But I have another question. I live in a climate that does not really get any chill hours. Probably plants will only be able to get maybe 45 chill hours here. They would be lucky to get 100 if it was an unusually cold winter. Now my question is, is there even a point in getting a 'low chill' variety? I mean, they are still not going to get anywhere close to their required chill hours. I know some people in this area have been able to get cherries from the low chill cherry varieties Royal Lee and Minnie Royal, but I have also heard (cannot verify) of 2 gardeners here have managed to get a few cherries from Bing, which obviously requires far many more chill hours than it gets here.

Either way, they are not going to meet their chill requirement. That being the case, will the low chill varieties produce a larger more reliable crop even if they do not get ANY chill hours? I do not think 45 chill hours is enough to trigger anything.

It is so warm here, I was thinking maybe I should just stick with the Bing cherry, that the low chill variety might not be any better. Because the cherries are not going to be influenced by chill (there isn't any).

    Bookmark   January 13, 2015 at 1:04PM
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fruitnut Z7 4500ft SW TX

Royal Lee and Minnie Royal will likely do far better in your climate than Bing. Cherries like Bing aren't low chill. If they are blooming you are likely getting more chilling than you think.

What model are you referring to when you state 45 hrs? Is that hrs below 45F? Temperatures above 45 are effective for chilling especially in cloudy/foggy weather.

I'd suggest growing varieties proven in your area. The San Diego chapter of CRFG has long lists of varieties that work in that area.

    Bookmark   January 13, 2015 at 1:47PM
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Socal2warm

Yes, I know the low chill varieties can definitely be grown with 0 chill hours below 45 ðF, though the trees do not seem to produce a huge crop, from what I have read online.

Of course they say low chill varieties are better for warmer climates. I am just questioning the conventional wisdom, when there is barely any chill at all. Will the yield from a cherry like Bing really be less than Royal Lee?

If I lived where I could even get 120 chill hours, I would definitely go with the Royal Lee, but as it is there is no way any cherry variety could even get close to receiving the necessary number of chill hours here.

And yes I am aware that temperatures a little above 45ðF can still count as chill hours, but I barely even get any of that here. Night temperatures dip 49ðF at their lowest, then back to 70ð in the day. I think the coldest night this winter was only 47ðF.

    Bookmark   January 13, 2015 at 3:05PM
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fruitnut Z7 4500ft SW TX

Bing sets zero fruit without pollination, zero, none, nada. So not only will you need to get it to bloom but you'll need to get a suitable pollinizer to bloom at the same time.

The really low chill fruits like Royal Lee don't have well defined chilling requirements. The number may be 2-300 hrs but those trees are really just looking for an excuse to drop their leaves and bloom. I can make grapes, and low chill blueberries bloom just by pruning. So if I had those low chill cherries I'd pull all the leaves off in Dec.

Bing will need some real chilling IMO to expect it to bloom. Not so with RL or MR. I've heard reports of blooming after no chilling. Main complaint is they don't always bloom together. That issue will be even worse with Bing. Go Stella or Lapins, self fertile varieties if you want to try something else.

Funny thing is thousands of guys in CA want to grow tropicals in those areas where it drops into 20s every yr. Go to a warm area and guys want to grow high chill fruits. Not knocking your desires, I'd be the same way, just find it somewhat interesting.

    Bookmark   January 13, 2015 at 3:44PM
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drew51 SE MI Z5b/6a

Besides the first year, I would be shocked if you got any fruit off the bing at all.

This post was edited by Drew51 on Tue, Jan 13, 15 at 15:50

    Bookmark   January 13, 2015 at 3:45PM
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Kippy(SoCal zone 10. Sunset Zone 24)

How accurate do you think the UCD chill hours actually are?

For my area something is wrong because it ranges from 1 hour to a couple hundred. Since we had frost and a couple of days it hardly got to the 50's something is off.

But I see my probably Seckel pear is still loosing leaves while 10feet away my probably Santa Barbara peach is covered in swelling buds. Both long established trees

    Bookmark   January 13, 2015 at 5:35PM
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MrsLizzyNorCal Suns17-USDA9b

Chill stuff puzzles me because I've heard SO much conflicting info. I'm in Santa Cruz, which I've heard gets either low chill, or possibly up to 500 hours. Yet I have an established Winter Nelis pear tree, which is said to need 800 hours, and it seems to do fine--it's had some very bountiful years. (my only trouble with it is some brown/black spot.)

    Bookmark   January 22, 2015 at 2:36AM
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drew51 SE MI Z5b/6a

I heard over 70% of the cherry crop was lost in CA due to low chill. Lizzy some pears and apples are way off on what's required. It is a mess and many cultivars are not well documented. Cherries though are fairly well documented. What is thought to be the chill requirement is way off on some apples and pears.

    Bookmark   January 22, 2015 at 7:48AM
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fireduck(10a)

very funny that SoCal2 would revive this thread after nearly 5 years ...haha. As I have stated many times in the past...unfortunately some growers (one in particular...DW) do seem to be chasing SoCal $$$ with their hype of low chill varieties. Some of those varieties simply are NOT rated correctly. Many gardeners end up spending money and lots of time...for nothing productive. Of course, others are legitimate low chillers. Sites like this are your best reference.

    Bookmark   January 22, 2015 at 11:21AM
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softmentor(z9/sunset13 CA desert)

In defense of Dave Willson and their listing of chill hours. they do listen to people who give polite and well articulated input. I was one of many why tried Earlytreat peach when they had it listed as 150 hours chill. It did not perform well here and I reported my results back to them. I would guess that they also received other input from other areas, but bottom line, they now list that variety as 450 chill hours.
I think they try to give honest values for chill requirements. And if there is one that is off, they listen to growers and gardeners and change when there is evidence. They are a HUGE nursery, and I usually don't like big, but they have proven themselves to me more than once. I give them top scores. and no, I don't work for them.

    Bookmark   January 22, 2015 at 11:15PM
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drew51 SE MI Z5b/6a

I like Dave Wilson Nursery too. It's so much better, leagues ahead of say other big nurseries like Gardens Alive or Proven Winners. Proven Winners does produce excellent plants too, but so little info compared to DWN, or should I say useful info. How many wholesale nurseries even give any info to consumers? The place rocks, the videos are awesome. The forums are cool too. I have talked to them numerous times, and they respond to consumers all the time I agree. Even complemented me on my garden. NO other wholesale nursery even knows who I am, let alone viewed and commented on my garden.

    Bookmark   January 22, 2015 at 11:54PM
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fireduck(10a)

I find it a bit odd that someone in zone 5 in Michigan would even enter into a discussion about low chill variety fruit trees. That being said...it is nice to hear DW will listen to gardeners now. Perhaps their methods have improved over the years. I have bought their trees for decades...and they have many fine trees/varieties. For many, many, years (going back over 30 years for me) their hype of several varieties were simply inaccurate (not even close on chill hrs). It was well known by active growers/retailers that you really need to do your own research if you live/grow in SoCal.

    Bookmark   January 23, 2015 at 9:49AM
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drew51 SE MI Z5b/6a

Fireduck,

Well I entered discussion because it became about Dave Wilson, and thought I would comment. Also they do offer high chill. I agree you need to do your homework.
Also some low chills do fine here, I have low chill blueberries that thrive here. Low chills may have a minimum amount of chill but that does not address how hardy they are. The only problem is them coming out of dormancy early since they easily meet chill requirements. With blueberries it's temperature related. At 45F and above they come out. But it doesn't get that warm here ever in the winter, or early spring, once temps hit 45F here, it is time to come out, so it's not a problem. Not sure how fruit trees respond though? I don't have any low chill trees.

    Bookmark   January 23, 2015 at 10:12AM
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Kippy(SoCal zone 10. Sunset Zone 24)

I find it interesting that for my county:

Goleta had 1 hour
Santa Barbara had either 14 or 87(83)
Santa Maria 214
and Lompoc where they are growing a lot of crops and is close to the ocean lists 375(342)

That more tells me the instruments need to be checked. Since we had a few days that barely made it out of the 40's and frost, that Goleta number is really wrong. Lompoc is normally colder, but not in that 45 degree and lower range than SB or Goleta, the wind off the ocean drops the temps, but also moderates the lows.

It is curious

    Bookmark   January 23, 2015 at 11:33AM
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MrsLizzyNorCal Suns17-USDA9b

Kippy, are you getting your chill hours from the UC Davis site or elsewhere? It does them by stations in each county, but my county is big and has coastal areas and inland areas, and unfortunately neither station is similar to my area so the rates are way off. I'd love to know of a site that used more stations!

    Bookmark   January 24, 2015 at 3:07PM
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Socal2warm

3rd update:
The Yoshino has begun leafing out at one spot, at the very top (this is the part that gets the most sun, and where I have been applying the most growth hormone). It's a very little plant, almost a seedling, and the upper branch is very thin and narrow, I am almost surprised the plant is able to send enough energy through up there to start leafing. The plant had tried to leaf before in two other areas, but those tiny leaflets never really grew, and turned brown after 2 weeks and fell off. Again, although it had previously been inactive for several months, I think the Yoshino was in a twilight zone on the brink of dormancy, but not quite.

One of the kwanzan plants is not doing anything. There is still a tiny little bud area that is green, but it has completely stopped (at least the bud has not turned brown). It's not really a bud, it's the inside of a bud, looks like the earliest beginnings of a sprout. The other kwanzan has only changed a little. It looks like it's trying to grow and come out of dormancy, but can't. That's the feeling I am getting from all three cherry seedlings, that there are tiny visible changes manifesting but the plants are struggling to find the energy to actually grow, or are just very reluctant. There are several small green bud areas that are stalled.

The Bing cherry tree, although the buds were growing at first, they seem to have stopped. They are still greenish, just not doing anything now.

So in conclusion, I would say that the application of gibberellic acid definitely had an effect, and initiated changes that proceed coming out of dormancy, and which might later make it easier for the plants to come out of dormancy. The hormone-induced growth seemed to happen mostly during spans of several sunny clear days in a row. And the growth also did not seem to be self-sustaining. It required continual application of the hormone, and when I stopped applying the hormone for 10 days, the growth seemed to stop. Probably gibberellic acid is only one of several different signals the plant uses to come out of dormancy, and so this single hormone alone was not really fully adequate. I think it could certainly "tip the scale", to help a fruit tree come out of dormancy, if other factors are favorable.

I have also thought about using another rest-breaking chemical, Thidiazuron (TDZ), in conjunction with gibberellic acid. Although from what I have read, TDZ is most effective when applied BEFORE the plant experiences chill, and reduces the necessary subsequent chill requirement.

    Bookmark   February 1, 2015 at 2:54PM
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