How much sun do pines need during winter dormancy?

[ACooke]

As I said above my trees all go no light full dormancy . But it’s zone 4 -25c. . What I’m trying to understand about your situation . Is why are you moving them from there summer spot . If it never goes below freezing and or just very temporary . What is stopping you from leaving them there in better light . Are you worried they will not get enough dormancy . Keep in mind I have no experience in such a temperate zone . Just trying to understand what your goals are .

I wouldn’t be moving them; they’ll be in a grow bed which the sun travels directly over in the warmer months but the suns path, when lower in the sky during the winter months makes a course that is for most of the day, obstructed by a house.

So full sun from just after dawn until early afternoon in the summer months (probably 7am - 1-2pm) eventually becomes very minimal direct sunlight in the cooler months.

That’s why i was curious if anyone knew whether the much cooler temperatures you mention are a necessity for the dormancy and if they are, whether a JBP could deal with the lack of direct sunlight through the cooler months if those months are cool enough to ‘force’ it in to dormancy.

 

[Paradox]

My trees get little to no sun all winter.
I never see a problem from it.

The mugo in post #35 turned brown because it dried out and the needles dessicated, not from lack of light. Look closely at the needles, they are all curled up and dried out.

 

[Frozentreehugger]

I wouldn’t be moving them; they’ll be in a grow bed which the sun travels directly over in the warmer months but the suns path, when lower in the sky during the winter months makes a course that is for most of the day, obstructed by a house.

So full sun from just after dawn until early afternoon in the summer months (probably 7am - 1-2pm) eventually becomes very minimal direct sunlight in the cooler months.

That’s why i was curious if anyone knew whether the much cooler temperatures you mention are a necessity for the dormancy and if they are, whether a JBP could deal with the lack of direct sunlight through the cooler months if those months are cool enough to ‘force’ it in to dormancy.

Then in my humble opinion your doing the best possible. At end of the day they will be fine with next to no or no sun if dormant . And I think there is something to be said about the natural light diminishing. In fall and increasing in spring in one spot . Some long time practitioners have talked of this . ( Dan Robinson for one ) if you have access to more sun it may be beneficial in early spring .

 

[penumbra]

I'm sure this varies by species, but what have your experiences been with keeping pines in winter dormancy with/without sunlight? Let's say popular pine species for now: Japanese Black Pine, Japanese White Pine, Scots Pine, Mugo Pine, etc. I'm planning to keep a Scots Pine in an unheated/unlit garage, but would it be wise to get a grow light if that's the case?

Seems like Brent from Evergreen Gardenworks say evergreens to fine in a garage: https://www.evergreengardenworks.com/overwint.htm

But I've seen others like Ryan Neil from Mirai begging to differ.

Your thoughts?

I am not sure anyone yet has the full answer. There are many questions about bonsai that will forever be debatable. I do my best to emulate nature as much as I can. As an example, winter days are shorter and quite often there are many grey days in my area. But there is never a period of sustained darkness. This therefore is my guide.

 

[ACooke]

Thanks @Frozentreehugger, and @penumbra . That’s definitely helpful. It’ll be interesting, at the very least, to experiment and see how they take it.

 

[Frozentreehugger]

I am not sure anyone yet has the full answer. There are many questions about bonsai that will forever be debatable. I do my best to emulate nature as much as I can. As an example, winter days are shorter and quite often there are many grey days in my area. But there is never a period of sustained darkness. This therefore is my guide.

we all try to minimize the possible damage in the dormant season . For me that means protection from no 1 enemy . Desiccating wind while frozen . So I try to have them freeze once and then thaw once . The complete dark . Does delay trees noticeable in spring . But they respond and catch up very fast once in the light . Would they do better in some winter light . Possible . But I’m not changing the other variables. Unfrozen I would be more concerned about complete dark . Outside in any light I would not be concerned . I think they will act very similar . And respond very well in the spring to strong light

 

[Bonsai Nut]

Since we are specifically talking about pines, I did a little deep diving here and read some papers to see if I could come up with a better answer.

First, it is important to agree that dormancy in pines is very different from dormancy in deciduous trees. Deciduous trees move into and out of dormancy slowly, and when they are dormant, they are truly asleep and could be in a cave for all they cared - as long as their roots don't dry out. Deciduous trees do not photosynthesize while dormant, and have only minimal respiration and transpiration.

Dormancy in pines looks a little different. Pines don't have a hard dormancy in the way deciduous trees do. As long as the ground is not frozen hard around the roots, and as long as the tree continues to have a supply of water, the tree can continue to photosynthesize, even in temperatures well below freezing (albeit at reduced rates). But the colder the temps, the less photosynthesis will occur. So a pine in deep snow that insulates roots and provides water, and with needles in full sun, will continue to photosynthesize. However just because they CAN doesn't mean they NEED to. And I haven't seen any studies that compared pines that were given light during the winter to pines that were kept in total darkness - to see if pines are stronger or otherwise benefit from winter sun.

 

[ShadyStump]

Topic adjacent
Does anyone know for sure if the same applies to broadleaf evergreens? Things like holly or whatnot, that are not conifers but still retain their green foliage through winter. I would suspect so, otherwise what's the evolutionary benefit of retaining the foliage?

 

[August]

Topic adjacent
Does anyone know for sure if the same applies to broadleaf evergreens? Things like holly or whatnot, that are not conifers but still retain their green foliage through winter. I would suspect so, otherwise what's the evolutionary benefit of retaining the foliage?

I dont know in so far as the photosynthesis during winter, but conversely I do know that cold dry winds have a much greater impact on broadleaf evergreens than anything else; or at least they do here.

 

[ShadyStump]

Of course, that's the evolutionary benefit of the needle-like foliage.

I imagine anything that keeps it's foliage year-round would either be photosynthesizing, or at the very least be saving energy.

 

[Frozentreehugger]

Since we are specifically talking about pines, I did a little deep diving here and read some papers to see if I could come up with a better answer.

First, it is important to agree that dormancy in pines is very different from dormancy in deciduous trees. Deciduous trees move into and out of dormancy slowly, and when they are dormant, they are truly asleep and could be in a cave for all they cared - as long as their roots don't dry out. Deciduous trees do not photosynthesize while dormant, and have only minimal respiration and transpiration.

Dormancy in pines looks a little different. Pines don't have a hard dormancy in the way deciduous trees do. As long as the ground is not frozen hard around the roots, and as long as the tree continues to have a supply of water, the tree can continue to photosynthesize, even in temperatures well below freezing (albeit at reduced rates). But the colder the temps, the less photosynthesis will occur. So a pine in deep snow that insulates roots and provides water, and with needles in full sun, will continue to photosynthesize. However just because they CAN doesn't mean they NEED to. And I haven't seen any studies that compared pines that were given light during the winter to pines that were kept in total darkness - to see if pines are stronger or otherwise benefit from winter sun.

This is what I wax getting at . Conifers with frozen footballs . Will survive fine without light . As I said the devil is dedicating winds . A full grown tree in nature even in extreme cold will have access to water unfrozen . In just a few feet deep in the soil . When photosynthesis takes place at what temp . Ambient hard to say . But as I said unfrozen roots . I would be scared to go full dark . And higher levels of light may be Useful . Lots of alpine conifers live in very cold conditions with high UV . In winter so depends on the species . Basically if conditions are correct they will photosynthesis . If not they will be dormant . My practise of frozen full dark all trees . Is normal practice in cold climates . For nursery trees , only experimentation is capable of answering can they benefit from increased light above freezing . But I think some caution is in order . Remember ther is a pot warm days in winter May stimulate the roots to much followed by more cold weather . Again why I try to freeze one and thaw once

 

[ACooke]

we all try to minimize the possible damage in the dormant season . For me that means protection from no 1 enemy . Desiccating wind while frozen . So I try to have them freeze once and then thaw once . The complete dark . Does delay trees noticeable in spring . But they respond and catch up very fast once in the light . Would they do better in some winter light . Possible . But I’m not changing the other variables. Unfrozen I would be more concerned about complete dark . Outside in any light I would not be concerned . I think they will act very similar . And respond very well in the spring to strong light

Perfect. That answer my wondering very concisely.

 

[Tieball]

Any pines I have stay outdoors all year long, even the harsh sub zero winter wind chills. The pines are generally in full exposure to natural weather. The trees get buried in snow and ice….thaw and freeze over again. And in spring the trees grow.

 

[MaciekA]

Topic adjacent
Does anyone know for sure if the same applies to broadleaf evergreens? Things like holly or whatnot, that are not conifers but still retain their green foliage through winter. I would suspect so, otherwise what's the evolutionary benefit of retaining the foliage?

I'm in the Willamette valley and I have an Ohi'a Lehua (metrosideros polymorpha) that has continued to push out and expand foliage / buds through the entirety of november (which was a fairly cold month) and during this brief warm spell in December (pineapple express / very wet jet stream).

This has been happening at a very slow rate, but we've been mostly between 0C / 32F and 10C / 50F during those times, with just a handful of days approaching 15.5C / 60F lately. Admittedly this is a Hawaiian native programmed to grow 365 days a year, but U of Hawaii has shown that it can handle down to -6C / 21.2F. And in any case, it's an example of a broadleaf evergreen which continues to grow (or as you suspect, productively photosynthesize / benefit) even in temperatures that send deciduous trees to sleep.

 

[cmeg1]

i’ve tried both ways with and without sun, and my favorite is for a Pine to be in the shaded light……….when it is very cold.
When it drops below freezing I shut the wooden lid of the cold frame………or keep under my home and it is dark in there.
When forcast to be above freezing I open the lid…….they seem much healthier this way.

Plus mold will take hold in a sealed dark environment if not frozen……quite quickly.

I open the lid to the frame ( a wooden box without a bottom 1.5’ in the ground in the shade with gravel ) on days and also let rain and some snow in there too………they freeze solid in the 3-4” grodan stonewool and have survived excellently ……results below in the pics!!!
Froze solid in the Grodan Stonewool mini-blocks and delta blocks( bigger size).

 

[ShadyStump]

I'm in the Willamette valley and I have an Ohi'a Lehua (metrosideros polymorpha) that has continued to push out and expand foliage / buds through the entirety of november (which was a fairly cold month) and during this brief warm spell in December (pineapple express / very wet jet stream).

This has been happening at a very slow rate, but we've been mostly between 0C / 32F and 10C / 50F during those times, with just a handful of days approaching 15.5C / 60F lately. Admittedly this is a Hawaiian native programmed to grow 365 days a year, but U of Hawaii has shown that it can handle down to -6C / 21.2F. And in any case, it's an example of a broadleaf evergreen which continues to grow (or as you suspect, productively photosynthesize / benefit) even in temperatures that send deciduous trees to sleep.

Thanks for that example. It's sufficient proof of concept for me.