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Extend winter dormancy by refrigerating and keeping the apex of a tree in the dark

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Darko Savic
Darko Savic Jan 11, 2022
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A system that refrigerates the apexes of fruit trees in orchards, thereby preventing the plants from coming out of winter dormancy too early. Turn it off only after the danger of frost has passed.
Early spring is often interrupted by a brief round of snow and frost in the northern hemisphere. The trees that come out of winter dormancy early are damaged by this. They cannot bear fruit that year. This means no cherries, plums, apricots, in entire regions.
How it works
An experiment
Firstly, let me say that this needs to be experimented with. I'm not sure whether keeping the apex of a tree at a freezing temperature and in the dark would actually prevent the plant from coming out of winter dormancy. I suspect it might, based on this:
"After bud dormancy is broken by adequate chilling, apically produced growth-promoting hormones move down the branches and stem and provide the stimulus for initiation of seasonal cambial growth."
So, what if we refrigerate and keep the apex in the dark, until the danger of frost has passed? It would generally need to be done only for a brief period of 1 to 3 weeks when it looks that spring has arrived, but a freezing rain/snow is still posible.
Peltier elements and liquid cooling
Similarly to how the light bulbs are hung in this image below, cooling units would be hung to power all the tree tops in an orchard.
Cooling unit
Each cooling unit would consist of:
  • a silicone tube that is wrapped around the apex area of a tree
  • a miniature pump that circulates the liquid coolant through the tube
  • a peltier element that cools the liquid on one side, and radiates excess heat on the other
  • a thermostat that keeps the unit running only when the temperatures are above freezing
A small water cooler, pwered by a peltier element:

Such a cooling unit would be the size of an old light bulb. It would be mounted just under the apex of each tree. A tube coming out of the cooler would wrap around the apex. An antifreeze type of liquid would circulate througout the tube, keeping the apex at around freezing temperature. A dark hood would be pulled over the entire apex area, keeping the sun away to additionally prevent the apex from producing the necessary hormones that cause the breakage of winter dormancy.
Depending on how many trees there are in an orchard, the Installation would take some time. But a day's worth of work saves a season worth of fruit.

[1]Theodore T. Kozlowski, Stephen G. Pallardy, in Growth Control in Woody Plants, 1997 - https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/bud-dormancy

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General comments

J. Nikola
J. Nikola6 months ago
I must admit this is a very interesting idea and this is why I think it could work.
Although it is guided by plant hormones, the main orchestrating factors of the dormancy are the reduction in daylight and the cold accumulation. However, cold deacclimation and bud dormancy release are not concurrent events; winter buds remain cold-acclimated after dormancy release under appropriate low-temperature conditions as long as meristem growth is not resumed, after which deacclimation is not any longer reversible.
Therefore, by controlling the main orchestrating factors we should have a higher chance of affecting the dormancy prolongation.
I would also like to comment on the cooling method. Here, a guy did a Peltier element cooling efficiency test and reported that only around 5% of the energy used to power the cooler gets used for cooling. He used 49.8W input and reduced the temperature of 250 ml water for 3.5 ºC (from 18 to 14.5) in 1 hour. Although it sounds very cool, I am not sure how effective could it be for the large system you proposed. What could be the alternatives or alternative power sources? Solar maybe?


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Darko Savic
Darko Savic6 months ago
J. Nikola Peltier elements are the smallest and simplest devices I know of that directly output heat or cold when voltage is applied. Such devices can be very small. Everything else (that I know of) requires compressors, etc.
Anything that touches the cold side of a Peltier element, freezes. That's good enough for what we need it to do.
Even if it's not very energy efficient it's a small and simple device that could be mounted on branches
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Dragan Otasevic
Dragan Otasevic6 months ago
Spring is approaching. A good time for a small experiment to see if this works. In an orchard of genetically identical trees, pick a few and keep their apexes frozen and covered. Will it delay blooming?
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