When Do You Remove Trees from Winter Protection?

[DrTolhur]

There's a lot of threads and discussions around how to overwinter, when to overwinter, and what to overwinter, but I don't recall seeing much about when to UNoverwinter. That is, when to take trees that are in some protected winter situation (garage, shed, greenhouse, what have you) and place them back out unprotected. So how do you decide when to do so?

My trees are currently in the garage, so they'll start to feel the warmer temperatures in the coming weeks, but with only one east-facing window, I don't know that they'll take much notice of changing daylight.

 

[JudyB]

Get ready for the shuffle! I myself don't take them out till freezing temps are gone, but I do have light source in my overwintering, so I don't have to shuffle...

 

[chicago1980]

Soon hopefully, but usually April or may. Location Chicago

 

[Dav4]

Apparently never if you live in Michigan

 

[Dav4]

There's a lot of threads and discussions around how to overwinter, when to overwinter, and what to overwinter, but I don't recall seeing much about when to UNoverwinter. That is, when to take trees that are in some protected winter situation (garage, shed, greenhouse, what have you) and place them back out unprotected. So how do you decide when to do so?

My trees are currently in the garage, so they'll start to feel the warmer temperatures in the coming weeks, but with only one east-facing window, I don't know that they'll take much notice of changing daylight.

Best thing to do is keep the garage as cold as possible for as long as possible. Once the real cold is done, I’d move the Uber cold hardy species- junipers, white pines, etc- out first as they are unlikely to be damaged by light freezes . Deciduous trees on the other hand need to be babied once they’ve broken dormancy.

 

[Lorax7]

Apparently never if you live in Michigan

That's not true. We have 4 seasons here in Michigan: June, July, August, and winter.

 

[WNC Bonsai]

I only have 4 in the garage and I leave them there until they start to pop buds. Oddly enough my slippery elm clump never did drop its leaves but the stems are first year sprouts from an air layered root. They have withstood several freezing nights out. The trees that are left outside stay clustered until they start to pop buds also. Then the shuffle has to begin. I delay repotting as long as possible because of the possibility of late freezes here in mid-to-late April. However my larches are starting to pop now so with those I have to get started.

 

[River's Edge]

That's not true. We have 4 seasons here in Michigan: June, July, August, and winter.

I heard it was two seasons, similar to most of Canada where they are referred to as winter and construction.

 

[Scorpius]

As early as mid March for me and as long as temps stay 20 and above. I find my maples leaf out later and I don't have to worry about frost so much.

 

[PA_Penjing]

I’m the same as scorpius, 20 and above some trees start to go outside, on the ground, in the shade. I try to keep things dormant as long as I can. Sunlight will wake my trees up too early. I’d leave them in the garage til bud pop but the garage is south facing and begins to heat up a little too much as the day light lengthens

 

[Deep Sea Diver]

Out here we have the “Keep ‘‘em on the bench outside forever Matey” group who end up furiously running about in their pajamas and overcoats shuttling trees into the garage late at night at the beginning of cold snaps… like all this past week. So these stay outside most all of the year.

…. And the other crowd who put the hardy ones on or in the ground, mulched in a bit. The rest in improvised cold frames under stairs, etc or even in small greenhouses. All these trees come out once night time temperatures are reliably above freezing. I’m the latter due all the young azaleas.

As @Dav4 sort of mentioned, Trees deacclimate quickly, some in a couple days but all but the recalcitrant ones within a 5-7 days. To reacclimate again takes weeks. So bring ‘em out early and one might end up babysitting their trees in the garage or laundry room for the duration.

Good Luck!
DSD sends

 

[DrTolhur]

I'm seeing some people make the decision based on the trees themselves (i.e. bud activity) and others based on temperature. I guess no surprise there that there's no consensus on when/how this process goes. One thing I wasn't clear on was whether or not the trees would start to break dormancy if kept in a darkish garage full time, but if they will, then that seems like the way to go. Our last frost date here is something like mid-May, though, so it seems likely I'll have to be keeping track of temperatures and bringing them back in when overnight lows drop. Hence, the "shuffling" JudyB alerted me to.
(For reference, almost all of my trees are maples along with a Chinese elm, boxwood, and Japanese hornbeam.)

 

[River's Edge]

For reference, almost all of my trees are maples along with a Chinese elm, boxwood, and Japanese hornbeam

In that case I would practice the shuffle, err on the side of protection with these species and your location. I am in a much warmer location 8b and some maple cultivars are touchy even here!

 

[Deep Sea Diver]

Hmm.... In bonsai the answer is Aways "It depends". I hope this is clear... but its a simplified explanation so further study will reveal more twists and turns.)

Trees have to be in Ectodormancy, the final stage of dormancy before they can "break bud etc. " This is when tree has accumulated the genetically requisite number of chilling units for that species.. Thus different species exit dormancy at different times...... and buds and roots do not exit dormancy at the same time. Roots lag buds considerably due to being evolved to being buried in the ground... or not because the trees are in pots and thus open to damage.

Once in ectodormancy there are two separate triggers for entering/exiting dormancy, photoperiod change and temperature change.

These often act together. i.e. In fall the photoperiod decreases while temperatures decrease and trees enter Paradormancy. That's when trees become cold acclimated... and eventually "cold hardy" during Endodormancy. btw: When the two triggers do not act in synch, the outlier is always temperature.

example: Temperatures plummeting in the fall.... that's when major damage to the non acclimated parts of the tree get damaged. ...and different tissues of trees don't cold acclimate at the same time... roots go "dormant" last.​

Yet exiting Ecodormancy things get even trickier as the temperature trigger nowadays often gets out of "synch" with the photoperiod trigger...

Note: the scientific data has documented the climatic temperature trigger has become more and more variable and possibly for longer stretches of time over the past 50 years (... and much less average snow cover.... etc.)​

Week long heat spells certainly thrust trees out of dormancy. When the normal cold temperatures return the non acclimated parts of the trees become damaged.

...buds and roots don't act together in leaving dormancy.... except that our trees are in pots, not in the ground... and pots are not insulators... on the bench in the wind the media temperatures can drop below the ambient temperature... but that's a whole 'nother story. ... and why I'm very conservative about putting trees in and taking trees out of protection.​

So perhaps that's why people are somewhat confused as how to approach the "when to protect" and "when to put trees back on the bench" situation. The situation is fluid and getting more so over decades of time.

Cheers
DSD sends

 

[Shogun610]

I shuffle now until temps don’t dip below freezing for repotted or worked on everything else is outside on ground and fine

 

[WNC Bonsai]

There is a big difference betwen areas such as the south and the northern tier. Down enre we go throjgh a lot of freeze thaw cycles and then about the beginning of March temps get above 60 during the day and don’t regularly reach freezing at night. Since by now out trees have met their chill temp requirement and day length is increasing many trees begin to wake up. My larch and my Chinese quince have green buds on them, and my maples are swelling. So soon the buds will pop and I have no choice but to start the game. For the last few years we regularly see hard freezes kn late April which play havoc with trees that have broken dormancy—just ask our apple growers! Last year we had one that did extensive damage to landscapes through the Asheville area. I even had a a Japanese hemlock that lost 2/3 of its newly extending buds. So we are in a new “normal” that will increasingly require doing the shuffle. As I have shown in the past I now group my senstive trees and repotted ones in the bed of my truck and shuutle them in and out of the garage as needed. I wish I had room for a hoop house to provide protection.

 

[MSU JBoots]

That's not true. We have 4 seasons here in Michigan: June, July, August, and winter.

Actually it’s fall, winter, spring, and construction.

I have been wondering this as well since it’s my first year doing bonsai and first winter. My trees are heeled in the ground so I figured I would wait until the buds are swelling since I need to repot a couple of them.

 

[WNC Bonsai]

Interestingly I was watching a Ryan Neil video on winter care and he said that several Mirai subscribers in Michigan have been experimenting with their hardiest trees by leaving them outside in winter instead of putting them in sheds, garages, window wells and other dark areas. He reasoned that this allows them to continue photosynthesizing later into fall and early winter so they build up more carbs and can better withstand the cold temps. It also puts them in a better position for the following spring and growing season since they have greater reserves of stored energy. These trees have subsequently done better the following growing seasons.

 

[DrTolhur]

Yeah, that definitely makes some sense for evergreen species. I only do deciduous, so there's no photosynthetic value while the leaves are off.

 

[MSU JBoots]

Well I’m in Michigan, here are my trees outside. I’ll let you know in a few weeks how they are doing. The snow picture is a little old but there is still snow on them now