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

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.

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

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

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

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.

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

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

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.

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

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.

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.

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

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.

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.

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.

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.

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.

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).

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.

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.

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.

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

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

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.)

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.

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.

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.

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.

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.

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.

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

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!

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.

Socal2warm here again (had to change usernames when the forum changed).

4th update:

All 3 ornamental cherries have leafed out. While the gibberellic acid may have induced premature budding, it may not have been such a good idea. Many of the initial leafs that sprouted out were somewhat deformed in shape, and some of them turned brown at the edges, like they got scorched.

You know what is really remarkable? The Bing cherry has burst forth full of leaf growth, it has really taken off. Meanwhile both the Royal Lee and Royal Minnie Lee have not experienced vigorous leaf growth. They have still not fully leafed out, and the leaves they do have are very small.

The Bing I bought seemed to be just a little more (maybe 1 year) established than the other fruiting cherries, so this suggests to me that, at least when the plants are young, how established the plants are plays a bigger role than what type of cultivar they are.

[quote]Has anyone clearly observed what symptoms appear as a result of low chill? [/quote]

You asked what effects lack of chill has? From what I have seen, delayed leafing, and when the plant does finally start to leaf there is a lack of vigor, like the plant is reluctant to grow. It is the middle of May right now and both my Royal Lee and Royal Minnie barely have any leaves, and the leaves they do have are very small and stunted. Almost all the leaves on the Royal Lee are coming out of the very top tip. I noticed this same pattern with my two Kanzan cherries too.

I still suspect that more mature cherry trees are somewhat better able to cope with inadequate chill. How established the tree is makes a big difference.

I posted this years ago, I am surprised this thread is still alive. I've learned quite a bit about lack of chill since then. I sold my Santa Cruz orchard and I now live in tropical and subtropical climates that don't get very much chill. On the North Shore of Kaua'i we get maybe 5-10 hours per year between 55F and 60F, and zero hours below 50F, and no apples will grow here at all. At 3,000 feet elevation, they can grow some varieties of apples, because they get many hours between 45F and 55F, but they still get none below 45F. In Santa Cruz, I did observe that a number of varieties failed because there were not enough hours between 32F and 45F. My conclusion is that some fruit trees are capable to satisfy their chill needs in the higher 45F-55F temperature range, and those would be what we consider "low chill". For example, Pettingill came from Seal Beach, where there are plenty of hours between 45F and 55F during Winter, but there are practically no hours below 45F. And it grows and fruits fine there, yet it will never grow at sea level in Hawaii.

The other significant factor is the amount of heat accumulated during the day during the cooler season. It does make a difference, especially if sun hits the branches. This process definitely interrupts the enzyme processes to bring trees into or out of dormancy. Any sun during warm weather spells will negate the chill accumulation process.

As for symptoms, lack of chill means delayed bloom, delayed leaf-out, and extended bloom cycles. Some varieties will still produce under such conditions, but fruit size will be inferior and ripening times will be greatly delayed. Kevin of Kuffel Creek Nursery in Riverside grows many varieties of apples under inadequate chill. He's in a part of Riverside that is Sunset zone 18 and therefore gets a lot more chill than elsewhere in Southern California, For him, some varieties leaf out and bloom in the middle of Summer, and others get plenty of chill with just the 150-300 hours of chill he gets annually.

I noticed this also. We had an unusually warm February with 2 weeks of constant sunny weather with clear skies. That is when the cherries started breaking out of dormancy. In March it got very cloudy again and the growth began coming to a halt. It really seemed like exposure to sunlight had a big part to play.

I have another fruit tree, where the upper part of the tree gets full sun and the lower part of the tree is mostly shaded by a wall, and it really seems the upper and lower parts of the tree are on two different cycles. The leaves on the upper part of the tree last much longer, while all the lower leaves fall off. The leaves on the upper part of the tree did not begin falling off until January. Then when it comes time for regrowth, the leaves on the bottom are the first to appear, because the bottom half of the tree has been in dormancy longer. The difference in timing is out of synch by about 6-8 weeks.

From what I have read in various places, one of the consequences of inadequate chill is that the fruit tree will not reliably send out fruit in all years; there will be some years where no fruit is produced at all.

It can also take much longer for the fruit tree to begin producing fruit in the first place. Fruit trees generally become more fruitful as they mature, so that can help counteract to some extent the lack of chill hours. (further research that I've done suggests it may take up to 10 years in this climate before I ever see ANY fruit on the Bing)

From various people's experience, it seems lack of winter warmth can make more of a difference than severity of cold. If the tree gets shaded, this can help reduce winter-time highs. The tree needs some cold nights, but intermediate day-time high temperatures can effectively "subtract" from the chill hours the tree experiences. So as long as these warmer temperatures are avoided, the tree may not need as much chill as you think.

I was reading [in another forum] about people's experiences growing Blenheim apricot trees in Orange County [California]. Blenheim is considered a medium-chill apricot. Apparently there are certain parts of O.C. where Blenheim will produce (the bottom of canyons near along the stream bed that funnels cold air in the winter). But back to the point, the main symptom of lack of chill hours seems to be that Blenheim will not produce fruit in all years (and the fruit yield is greatly diminished). It's hard to say whether this has more to do with some winters being exceptionally cold (or having few warm days), or whether the tree just finally decides to fruit after having gone the last two years without producing (basically all that pent-up energy). Probably a combination of the two factors, I think.

In my experience I have also found that trees that ideally require a higher degree of chill hours than the climate they are in often tend to do better planted in partial shade (even trees that are supposedly "sun-loving". The shade helps keep winter days from getting too warm.

Some people may wonder how chill actually physiologically interacts with deciduous trees. I believe I have an answer. The plant naturally produces a certain hormone. When the temperatures fall below a certain level, that production of that hormone slows down, since its enzymatic production is very temperature dependent. Of course the production of other growth factors also ceases at the same time. It takes many weeks for the hormone already pooled up in the plant to be slowly metabolized away. When the hormone levels are at their lowest levels, after experiencing adequate winter chill, only then is the plant able to respond to warmer conditions and come out of dormancy. So exceptionally warm winter days can really detract from the chill hours, because that inhibitory hormone will start to pool again, and the plant will need many more cold days to have time to gradually eliminate it.

Parker. What is the source of your temps? I live in Clairemont and we get below 47 many nights of the year. On occasion we even get frost. This past week of Nov. we have already had a 40 night.

Last night

Rainier Cherry setting blossom south of Los Angeles. It's in zone 10, but we had an unusually cold winter this year.

Interestingly it bloomed just 1 week after my Royal Minnie Lee. The Rainier is in a spot that is partially shaded.

(Don't pay any attention to the generic looking cherry tag attached to the tree, it was cleary marked as Rainier when I bought it)

As my cherries have now been in the ground for almost 2 years, I can now comment about the effect lack of chill has. The effect appears to be much more pronounced on all the cherries that receive full sun exposure. It is now July, and the leaf size of most of the cherries is small to undersized, and not all sections of the tree have leaves. The leaves are primarily on the tips of the branches, or on some of the trees near the base, closer to the ground. I suspect this is due to lack of vigor, but it seems even after several months the leaf growth has not been able to catch up. It is as if the growth just sort of stalled, and now the growth is very slow. I suspect there may be a feedback cycle, and because of the inadequate chill the plant has not been able to come totally out of dormancy, in terms of circulating hormone levels in the plant.

Interestingly the Bing cherry seems to be growing much more vigorously than the others. It is full of leaves, and the leaves are big and full-sized. All this is in the lower part of the tree though; the top branch is a little sparse of leaves, and there are only a few little leaves coming out of the top tip. I am thinking this may be because the top gets more sun exposure. Interesting that the Bing appears to be growing more vigorously than the Royal Lee cherries. But one possible factor, it is one year older than the Royal Lee trees, so that may have given it a little more time to become established.

The cherries with partial shade appear to be doing better than the ones in full sun, and also flowered and leafed out earlier.

The full-sized kwanzan (flowering) cherry that I planted in January last year appears to have very sparse leaf coverage, and very small leaves. It is obvious it did not get adequate chill (despite this past winter being colder than usual). I would have thought that by July its leaf growth might have been able to catch up, but that is not the case.

Both the kwanzan seedlings have survived. One has 2 medium sized leaves on it and 2 tiny leaves; the other has many small leaves on it now, and has sent up a tiny little new branch (more like just a stem) from the top. I have been making sure they receive water and that the soil does not get too dry. The little Yoshino seedling appears to be doing about as well as the kwanzan. Growth on all the cherries appears to be very slow (though the Bing has put out some new branches).

The Blenheim apricot has done well; there were even 11 fruits on the tree this year, though they were a little small and a few of them were undersized or fell off the tree before halfway before ripening. Pretty good considering that Blenheim is not really a "low chill" variety (supposedly requires 400 chill hours). Some fruits may be more "adaptable" than other fruits, though.

Both of my Royal Lee/Royal Minnie cherries have a single blossom on them right now. The flowers appeared a few days before Christmas. The Royal Lee looks like it is beginning to bud out some new leaves, while the Royal Minnie still has some leaves on it. I guess not having enough chill can make fruit trees a little confused. Both Royal Lee/Royal Minnie Lee have a very low chill requirement so maybe it was easier for them to become confused by a short period of unusually cold (and cloudy/rainy) weather followed by a week of relative warmth and sun.

i have 2 Pomegranate trees that produced 3 yrs in a row

last winter was very mild.

this year, neither gave me even 1 flower.

I just went to a fruit tree for warm climates talk. There was a suggestion to paint your trees white in winter if you feel you are just on the edge of getting enough chill. Also plant on north sides of houses and walls so that trees stand in shade in winter and get sun in summer at ripening time.

We've only got like 155 hours right now in the coastal Los Angeles area, Eva's pride and Tropic snow are already bloomed out, and the desert delight looks about ready to. I think usually by now we should have 300+ hours.