Ever Use Ice To Stimulate Cold Dormancy/Chill Hours

Firstflush

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Old nurserymen recommended using some ice on the soil around the crown of a tree to simulate cold dormancy or chill hours, where required. I’m in 10b and got a hold of an eastern lilac. They can’t do well here, not cold enough. I emptied the stinky old ice maker one season a few times a foot or more off the crown and got a a partial bloom one year. Pretty nice! Trickster.....

Question: Do you think putting a limited amount of ice around a JM for a week or two in the winter would benefit the trees health and the following seasons bud push here in Southern California?
 

Wires_Guy_wires

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I use ice deposits from my fridge and freezer to water my tropicals and they don't seem to be affected by it. They most certainly die at low temperatures.

I think you're going to need a lot of ice.. So much even that it might be better to just shove the entire tree in a fridge or freezer.
 

LooselyWired

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The number of cold hours a deciduous tree needs in dormancy is around 1,000 hours. You would be icing the tree 24/7 for six weeks. That is a lot of ice. I have heard of people using the fridge. Ask a florist if they can spare some cooler space for the winter. It may work, or not, but it is more workable solution. Failing that, buy a shaved ice machine and enjoy sno cones all winter. 🥶
 

Bonsai Nut

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Check out this excellent article on Chill Hour requirements for Fruiting Trees in California (from Dave Wilson Nursery). Many of the findings are likely applicable to flowering trees with cold requirements (since we are most interested in the successful development of flower buds). Excerpt:

How a deciduous fruit tree actually accumulates winter chilling is more complex than represented by the easy-to-use 45°F model. Research indicates fruit tree chilling 1) does not occur below about 30-34°F, 2) occurs also above 45°F to about 55°F, 3) is accumulated most effectively in the 35-50°F range, 4) is accumulated most effectively early in the dormant period, and 5) in early dormancy can be reversed by temperatures above 60°F. Chilling calculation methods such as the 32-45°F model, Utah model, Low Chilling model, Mean Temperature model and Dynamic model incorporate some or all of these findings. To date, all models tend to give significantly different results for different climates.
 

ShadyStump

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I was under the impression that @Firstflush was speaking of just jump starting dormancy artificially rather than holding it dormant the entire time. Theoretically, you could get a plant to go dormant with this ice technique, and then rly on the weather to hold it there just long enough once the process is started.
I'm interested because in my area the winters have been terribly mild the past few years and it's taking a toll on local orchards, and I'm looking into turning one of this years garden peppers into a bonchi, so I'm researching dormancy now.
 

Firstflush

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Always the discussion on JMs not doing well in areas without cooler/cold winters. I see the point brought up all over the web. I was just considering improving my JMs health with our warm winters by the above mentioned methodology.
 

ShadyStump

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I would imagine that once you can induce dormancy in full, even a very mild winter will hold it through to spring under normal conditions. Ice until it's asleep, then put it right back where it usually lives. Probably species specific to a great extent, but as a general rule maybe.
 

Eric Group

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Buy trees that do well in the climate you live in. Bonsai is not easy. It is virtually impossible when trying to force a tree that needs a cold environment to grow in a warm environment. You will at best get a few good years, but eventually they become exhausted and die. I live in SC- right on the edge of being too warm for some trees I keep, like JWP.. but it certainly is too warm for trees like Larch for example. So, even though I like them, I just do not own any. Some people try to do tropicals in environments where they have to be kept i doors for large portions of the year, but they just do not do as well as say South Florida or something like that..
 

Bonsai Nut

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Buy trees that do well in the climate you live in. Bonsai is not easy. It is virtually impossible when trying to force a tree that needs a cold environment to grow in a warm environment. You will at best get a few good years, but eventually they become exhausted and die. I live in SC- right on the edge of being too warm for some trees I keep, like JWP.. but it certainly is too warm for trees like Larch for example. So, even though I like them, I just do not own any. Some people try to do tropicals in environments where they have to be kept i doors for large portions of the year, but they just do not do as well as say South Florida or something like that..

I agree - having tried, and failed, with some trees that clearly weren't suitable for Southern California. The best example I can think of is every Christmas when the big box stores fill up with small potted "Christmas trees" that people buy because they would rather have a "live tree" than a cut tree. In almost all cases they are cold hardy species that aren't going to last one summer in California hot and dry conditions. So there is literally no practical difference between buying a cut tree and a tree in a pot... because they are both going to the land fill.

However... there are some trees that are right on the edge. In this case, the OP is specifically asking about cold degree days requirements in order for flower bud set on a lilac. It isn't a question of whether the lilac will survive or not. It is a question of whether it will get enough cold to bloom. I happen to have done a fair amount of research on stone fruits - because I wanted two different peaches in my orchard area with my citrus trees. California is the land of micro-climates, where you can grow some trees just fine in a coastal valley, when they won't thrive on a ridgeline 1/2 mile away. Of the two peach trees I ended up with, one fruited very dependably every year, while the second fruited only about 50% of the time - depending upon the type of winter we had had. It wasn't just about the "cold" - it was about the nature of the cold. A nice long cool period was much better than a short, deep cold snap. If I thought dumping ice on the tree for five days might have helped... I might have tried it.
 

leatherback

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I would imagine that once you can induce dormancy in full, even a very mild winter will hold it through to spring under normal conditions. Ice until it's asleep, then put it right back where it usually lives. Probably species specific to a great extent, but as a general rule maybe.
Somehow I think this would be an error. If it is not cold enought for trees to enter dormancy, why would it be cold enough to remain dormant?
 

Firstflush

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FYI, JMs all over the place here in the ground as garden trees .....Southern California.
There are some real nice old specimens in my neighborhood...the std green A. Palmatums do best.
Maybe I ask a neighbor for an air layer of an old established JM, where they are used to growing conditions here.

You also see the more boutique JM varieties fried all over the neighborhood. People have thousands and thousands of dollars in poorly growing yard trees here as well.
 

ShadyStump

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Somehow I think this would be an error. If it is not cold enought for trees to enter dormancy, why would it be cold enough to remain dormant?
I'm thinking this knowing that certain perennial plants require a hard frost to go dormant. I can't imagine that many trees aren't similar. It's the age old quandary of what about the fall and winter months really causes dormancy: cold temperatures or lowered sunlight? Often the answer is "yes." It takes a bit of both. So, if you don't have enough of one, you might be able to artificially simulate it to induce dormancy, and dormancy be maintained by the natural presence of the other. In this case, ice to chill the tree, in another maybe a shade of some sort, in others a bit of both. Depends on the tree, the climate, etc. and there's only one way to find out.
 

Grovic

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I was under the impression that @Firstflush was speaking of just jump starting dormancy artificially rather than holding it dormant the entire time. Theoretically, you could get a plant to go dormant with this ice technique, and then rly on the weather to hold it there just long enough once the process is started.
I'm interested because in my area the winters have been terribly mild the past few years and it's taking a toll on local orchards, and I'm looking into turning one of this years garden peppers into a bonchi, so I'm researching dormancy now.
My hometown is known for their apple orchards, and they too are struggling with mild winters recently. One of the techniques they use is to turn on the sprinklers prior to a freezing cold night, the trees get soaked and when the temperatures drop, they get a nice thick layer of ice which provides additional cold hours, even if the temps rise above freezing the tree remains frozen for a while.
 

Grovic

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My hometown is known for their apple orchards, and they too are struggling with mild winters recently. One of the techniques they use is to turn on the sprinklers prior to a freezing cold night, the trees get soaked and when the temperatures drop, they get a nice thick layer of ice which provides additional cold hours, even if the temps rise above freezing the tree remains frozen for a while.
But you need to have at least a couple below freezing nights every week.
 

leatherback

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My hometown is known for their apple orchards, and they too are struggling with mild winters recently. One of the techniques they use is to turn on the sprinklers prior to a freezing cold night, the trees get soaked and when the temperatures drop, they get a nice thick layer of ice which provides additional cold hours, even if the temps rise above freezing the tree remains frozen for a while.
Interesting .. But.. I thought chill hours for dormancy are counted on non-frost hours below 7c or so (below 45F or so)?
 

0soyoung

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But you need to have at least a couple below freezing nights every week.
I don't think it is below 0C/32F (freezing) but below some temperature like 5C/40F or maybe even below a temperature threshold as warm as 10C/50C. We have a member who grows acer palmatums in the Azores which is a USDA zone 11, which means winters are only about this cold (i.e., somewhere around 7C).
 

ShadyStump

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So far, I think the suspicions of it taking both a bit of cold and a bit of dark to spark dormancy are supported. I imagine many trees- at least deciduous trees- have a certain though varied range in which almost any combination of low temperatures and low daylight hours is enough, though I suspect that cold is the kicker.
My hometown is known for their apple orchards, and they too are struggling with mild winters recently. One of the techniques they use is to turn on the sprinklers prior to a freezing cold night, the trees get soaked and when the temperatures drop, they get a nice thick layer of ice which provides additional cold hours, even if the temps rise above freezing the tree remains frozen for a while.
But you need to have at least a couple below freezing nights every week.
I'll have to experiment with this this year. We just moved into our new home, and there are a couple very old apple trees in the back that produced nothing this year, and production in our region (once known for it's orchards) has suffered heavily the past few years. I think the first week it looks like several near freezing nights in a row that I'll go give them a spray each night. Super charge their dormancy, and maybe they'll sleep through the spring frosts that have devastated blossoms the last couple years, or at least weather them better.
 

Grovic

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Interesting .. But.. I thought chill hours for dormancy are counted on non-frost hours below 7c or so (below 45F or so)?
Not sure, but that's what they do, I think the goal is to keep the tree in the chill hours range (whatever that range is) for a longer time. It really is a nice sight to watch a frozen orchard being hit by the sunlight.
 

Leo in N E Illinois

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Climate zone envy. It took me a long time to accept that I can not grow every tree that captures my imagination. Many I delight in seeing will not survive my cold winters.

I am now much more focused on trees that come from my local forests. So much easier to care for. And if you do the "deep dive" into your native flora, there are always very interesting and uncommon species that are locally native. It can be just as satisfying as raising the exotics.
 

MrWunderful

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I thought the reason JM bonsai dont thrive in SoCal like conditions is the lack of temperature differential between day and night. Maybe I read that here?
 

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