How much sun do pines need during winter dormancy?

[PA_Penjing]

never had a winter casualty yet, water logged soil is probably a bigger threat to my pines while dormant than actual temperature. You WILL have casualties at zone 4 if you dont protect at a certain point. I'd say darkness before death.

.. felt guilty for not giving a black n white.. so there

 

[ShadyStump]

Why bury your trees? They can't heat themselfs like humans do?
Mulch will be frozen and i think the underlaying trees will be too.

So only indoors will make a difference..

Or am i wrong? Pleace correct me if i'm wrong.
I find this an interesting subject.

Came for learning then saw this fun little foray into thermodynamics... which I know less about than bonsai (which isn't saying anything flattering) but enough to make sense of this one.

Mulching around the trees allows the outside layer of mulch to absorb the brunt of nasty weather- layers of ice, stiff winds, heavy snow, etc.- that might otherwise damage the tree. It's not just temperature, but actual mechanical damage that can be done by winter storms. That said, a layer of mulch will also help insulate the tree, which, even if it doesn't prevent the high and low temperature extremes, will steady the rates at which the fluctuations between those extremes progress, also preventing damage. Essentially, a temperature fluctuation of of 15 degrees or more over an hour and a half as a storm blows in will be stretched out over three or four hours for the tree, reducing shock.
In nature, the sheer mass of the ground helps hold temperature and will do this, but for bonsai we have to find ways to do it artificially, hence this very informative thread.

 

[PA_Penjing]

Why bury your trees? They can't heat themselfs like humans do?
Mulch will be frozen and i think the underlaying trees will be too.

So only indoors will make a difference..

Or am i wrong? Pleace correct me if i'm wrong.
I find this an interesting subject.

Edit: this was pretty much fully covered above, my head is InThe clouds today.


Stacking onto the comment above, which is correct. The ground also stays at a stable temperature fairly higher than the atmosphere. It might be 32 degrees in the first couple of inches, and warmer below that, but that’s plenty warm enough for any hardy tree. It’s the roots that are most sensitive on a tree to the temperature. In nature they are kept at very reasonable temp all year long. In a shallow bonsai pot on a -15 degree night? Your talking about roots experiencing temperatures almost 50 degrees below what the “wild” tree next to is dealing with. That’s why burying pots “in theory “ is the best way to protect a tree. Unfortunately in practice, I can’t leave them susceptible to rodents and heavy snow loads

 

[AlainK]

rodents

Ach ! I understand.
I live in town, very few rodents here. One of the only troubles is blackbirds ripping the soil of recently potted bonsai, or tearing off the moss on older ones....

 

[Frozentreehugger]

Zone 4 Canada that means -25 to -30 C for several weeks in winter . Like you all . I use what I have . All my cold hardy trees get sane care . Stay on bench . Until well frozen .Then insulated un heated building no light complete dark . They are still there today -4c overnight . My experience and belief is . Frozen roots no light no need of water compete dormancy . I worry more about . Warm weather in fall and spring . Thaw freeze cycle more dangerous . I don’t open the door they stay there until . Slight football melt . The wind protection is critical . Zone 5 plants have survived with this care. Others here . Have far less success . With hurrying trees beside buildings and even covered n snow . Even some 2 plants can die . The wind and frozen roots and or the freeze thaw cycles and LIGHT . Is dangerous . I am fully aware of the mixed thinking . That trees with light may have a health advantage . But I believe my system is best with what I have . Trees are delayed compared to. Trees in the yard but respond and go active fast in spring . I am going to try a large container . With dry. Turface ( oil dry) product to burry pots in with heating coils to keep roots above freezing next year .goal is for first year collected trees. Severed air layers and possible fall repots .

 

[Potawatomi13]

Consider growth rings of trees. Spring/Summer broad rings most growth. Fall/Winter narrow rings little growth but still growth, activity happening. Even in cold rings still developing so is lifes activity.

 

[Bnana]

Light is not only used for photosynthesis bit also to assess day length and this seasonal timing. That's at much lower light levels.
A pine covered in snow or in a shed with a North facing window still registers day length. Therefore it "knows" when spring is coming.

 

[SininCincinnati]

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 just overwintered 2 Chinese elms and 2 junipers in my garage with no sunlight the entire winter. Both my elms are budding right now.

 

[Frozentreehugger]

Light is not only used for photosynthesis bit also to assess day length and this seasonal timing. That's at much lower light levels.
A pine covered in snow or in a shed with a North facing window still registers day length. Therefore it "knows" when spring is coming.

Wondered about the day length . Light thing for a long time . My trees go cinolete dark no light during the freeze time . All hardy trees . So no means if assessing day length . Does not seem to effect them . When they come out in spring . Studies have shown that maples will lead out in dark . After extended time so you can’t stop it . Just saying I don’t think light and day length is as important as some believe . Maybe it’s the fact trees are froze and when they thaw they start to respond to day length but who knows

 

[Bnana]

They will eventually start growing without light cues but they definitely use daylength and temperature sums to time budding out. There's a large body of literature on this.
In bonsai this timing is less important than in the wild but even at low levels light affects the timing of trees.

 

[Paradox]

Its definitely a combo of temperature and light. My trees start swelling buds in a closed coldframe

 

[Frozentreehugger]

Like I said mine go full dark . I think the jury is still out from what I have read . About what triggers them . Mine come out as soon as I’m sure we won’t get hard freezes say below -5c so it’s still plenty early for the dicid . To swell buds . Example the native maples . Are delayed compared to parent tree in yard . But is that light . Temp . Access to soil water . They seem to catch up quick once outside . Earliest here is silver maple . It starts swelling buds in mid winter towards end of February . Can be -20c is that light levels or genetics . I do know that if roots and tree frozen . No light is needed . Will it help speed up in spring . In a less severe climate roots not frozen I think I would want my trees to have light . But freeze thaw and winter wind are the tree killers . Zone 4 also some proof . Tree death in nature shows up now early spring . All of a sudden conifers have dead leaves . Were green in winter . But frozen . Even a discarded x mass tree stays green till spring outside .

 

[Bnana]

These things have been studied extensively but the relative importance of temperature and photosignals (timing and spectral composition) differ between species. See https://www.sciencedirect.com/science/article/abs/pii/S0168192312002006 for example.

 

[n8]

Bjorn in Nashville. A couple days in the teens Fº in February, remainder around freezing.

Eeesh. Watching his assistant pull up towards his other wrist while cutting that plastic at 2:20. Knife control!

 

[Bonsai Noodles]

I believe that where winter temps are consistently in the mid 30’s F or colder, the pines, regardless of species, are metabolically so slow as to not require any light... think alpine evergreens under 10 feet of snow. I’ve personally kept jbp, jrp, and shimpaku in a garage with one north facing window for upwards of 4 months every winter, frozen on the concrete floor. For over a decade, they went in at thanksgiving and went out around April first and never skipped a beat. This was in MA over a decade when we still had consistently cold winters and I could keep them frozen. I’d say all bets are off if the temps hover at or over 40 F for more then a few days, though. Down here in tropical 7b N GA, those same trees stay on my benches all winter except for during the coldest week or two, soaking up whatever sun hits my backyard this time of year.

I think I'm at that point in my bonsai journey where I can slowly begin giving my two cents of knowledge, rather than simply take in knowledge from all the experienced folk. With that being said, I'd like to give insights on an experiment I did that seem to somewhat confirm what @Dav4 is saying.

In this experiment, I had a mugo pine that had two trunks. The tree was stored in a cold shelter (unheated garage) with a grow light (brand: Spider). Over the course of the winter, the temperature fluctuated between 20F to 40F in the garage, more often than not above freezing (32F). I tried to somewhat control this temperature using a similar system that @JudyB uses. Importantly, one trunk received more light than the other. You will see the result of this experiment below.

Clearly, one side of this mugo pine is thriving, whereas the other not so much. The trunk that received less sunlight, right now, will have foliage that easily pulls off. I will monitor how the buds do over the next few weeks, but I would not be surprised about dieback. This doesn't mean that storing a mugo pine without sunlight will kill it. However, it does mean that a mugo pine may begin "prioritizing" which foliage/branches to keep if only one portion receives sunlight. In other words, this mugo pine didn't go fully dormant because of my temperature control. My takeaway: if our local climate or cold shelter is above freezing so that the tree is metabolically active, then the tree likely needs sunlight. If there is uneven amount of sunlight on certain parts of the tree (at least in mugo pines), the tree may begin prioritizing which foliage/branches to keep. This is in line with what I have observed with shaded parts of trees. How come trees buried under snow don't lose branches? My garden Scot's pines look fine, for example. The key difference is that photosynthesis and transpiration is occurring when you store these trees in a cold shelter. There is a difference between trees grown in a pot vs in the ground. I assume that you would not observe this if you kept trees buried under snow, below freezing over the winter. I probably could have, since it's a mugo pine. However, for sake of adding knowledge to the community, I took a hit on this tree

I would also like to note that talking to people in YOUR local climate is paramount. There were people in the MN Bonsai Club that have consistently noticed that winter sunlight leads to better ramification in ponderosa pines. But can they live without sunlight? According to MN people, yes. However, if you're someone like Ryan Neil out in the PNW, as he says, pines do much better if they have sunlight in the winter. Why? Because there is transpiration and photosynthesis going on at those winter temperatures. In MN, transpiration is more or less halted. BUT. In the garage or cold shelter, maybe not so...

Hope this contributed to the discussion!

 

[ACooke]

Digging up an oldie here, but very interesting.

The above post touches on this but i was wondering if anyone has any input in to how necessary direct sunlight is through-out a winter where temperatures are easily high enough (avg. ~45°f - 65°f) that metabolic processes proceed (i presume) but where sunlight is ambient for ~10hrs due to the suns path being almost entirely obstructed as opposed to having good, direct sunlight for ~6hrs for the other half of the year?

Is the ambient light likely enough to tide a pine over.

Or is the lower levels/inndirect sunlight potentially fatal due to the higher temps. Ie. The reason pines survive no-light environments is entirely that they’re frosted in to dormancy?

Sorry, i think that above has been alluded to, perhaps even explicitly stated, but was hoping someone may have some experience with the higher-temp scenario?

 

[hemmy]

The above post touches on this but i was wondering if anyone has any input in to how necessary direct sunlight is through-out a winter where temperatures are easily high enough (avg. ~45°f - 65°f) that metabolic processes proceed (i presume) but where sunlight is ambient for ~10hrs due to the suns path being almost entirely obstructed as opposed to having good, direct sunlight for ~6hrs for the other half of the year?

Outdoor shade, partial shade, and indirect sunlight are all quite a bit stronger than indoors even when close to a window. There are some apps that can measure light intensity. They aren’t not accurate but can give you an idea of relative differences. You’ll want as much sun as possible when they start to grow in early Spring. At some point, too much shade will slow growth rate and vigor which will translate to poor ramification after pruning techniques. Make sure to rotate the pots periodically throughout the year to get even light to all sides of the trees.

That was close to my winter temp range in coastal SoCal for 10yrs. Japanese black pines would wake up and start candle growth pretty early in Spring, 2-3 months earlier than my current USDA Zone 6b area where we get “real” winter (consistent freezes). I’m not sure what the growth trigger was, daylight length or some marginal temperature dormancy requirement met.

 

[ShadyStump]

There's also a wide differential between species to account for.
It doesn't take much at all to keep a piñon pine dormant once it's there, and they don't need a great deal of chill hours; but ponderosa may wake up in the same conditions, and may not have slept long enough.
These are just my observations from living where the example species I just gave are prevalent.

There's also a sort of vin diagram gray area where trees can substitute chill hours, sunlight, and temperature one for the other to a certain extent. This too varies by species, and there's very little data on that.

 

[ACooke]

Sounds like it might just be a trial an error thing for me. I’m referring mostly to JBP’s but haven’t yet purchased any so i’m kind of tossing up whether to flick that idea in favor of less sun-thirsty options (begrudgingly, as i’d really love to work with a few JBP’s).

The warmer months, they should over 6hrs of solid, direct Australian sun. Winter, they’ll be shaded out by tree and and a house so will probably get an hr or 2 of direct sunlight at best, i’d think. So it’s mainly going to come down to how they tolerate the 45°f - 65°f ‘dormancy’ period without direct sunlight (but decent indirect).

Anyway - i’ll do some more thinking as to whether i try some JBP’s in culminating with some other species (a radiata/monterey pine may be a better option), or move on completely to some more shade tolerant species.

 

[Frozentreehugger]

Sounds like it might just be a trial an error thing for me. I’m referring mostly to JBP’s but haven’t yet purchased any so i’m kind of tossing up whether to flick that idea in favor of less sun-thirsty options (begrudgingly, as i’d really love to work with a few JBP’s).

The warmer months, they should over 6hrs of solid, direct Australian sun. Winter, they’ll be shaded out by tree and and a house so will probably get an hr or 2 of direct sunlight at best, i’d think. So it’s mainly going to come down to how they tolerate the 45°f - 65°f ‘dormancy’ period without direct sunlight (but decent indirect).

Anyway - i’ll do some more thinking as to whether i try some JBP’s in culminating with some other species (a radiata/monterey pine may be a better option), or move on completely to some more shade tolerant species.

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 .