Hardiness zones and wintering guidance please?

[PierreR]

I have a couple small trees, that are listed as Zone 5 and 6. When I look it up, I'm seeing temps of -23 to -29C (-10 to -20F) for zone 5a/b and -18 to -23C (0 to -10F) for zone 6a/b.

My question/s:
Are these temps the lowest the plant can take in short bursts, say 2-3 days duration? Or do those temps cover a broader window, say 3 weeks to a month? I realize that might be an extreme.

Seeing as I'm in zone 2b/3a, These trees will need protection. My thoughts are to utilize a window well, plants in, then sealed in with that foiled/bubble insulation allowing the heat loss from the window to raise the temp in the shelter. I suspect I could hold -10 to -20C, even if I had to open the window a tad on super cold days. Would you think this to be sufficient? There would be no sunlight reaching the trees.

No doubt we will see a few -40 and colder days. Not to many I hope. We hit a spell last winter, where liquid propane started to gel.

I'd like to hear your thoughts.

 

[Bunjeh]

This is about the best article I have found on the subject.

http://www.bonsai4me.com/Basics/Basics_WinterCare.html

 

[Dav4]

Those ratings are based on the trees being planted in the landscape. A zone 6 tree, planted in the landscape, should be able to handle temps that approach -10 f occasionally. A zone 6 tree would likely not do well if the temps hovered between 0 and -10 F for weeks on end. Having said that, experimentation might be in order. Get yourself a min max thermometer to record the temps this winter and see what happens.

 

[wireme]

I think your plan is good, definitely keep a max-min thermometer in there to monitor temps, may even get warmer than you'd like.
I'd be tempted to fill the well with mulch too, right over the trees, moist mulch up to the pot rim and dryer mulch above but that plan is a bit of guesswork and hope regarding moisture needs through the winter.
My mom kept a small fruiting fig tree planted in the ground alive here in 3b for about 15 years by bending it to the ground and covering it with a pile of straw every year.
Maybe just dry mulch to the pot rim so you could open the window and water when needed.

 

[wireme]

I haven't tried to keep many plants not hardy to my zone, last year had 50 or so Japanese quince seedlings buried 18" deep in pumice, they all did fine, we'll see if it works again. Not sure their zone hardiness but pretty sure it's not zone 3!

 

[PierreR]

Thanks @Bunjeh. I have read this, and a lot from this site actually. I find it funny in that article, it says the ground may freeze several inches deep. The town water pipes here are burried a minimum 10 feet deep to protect against freezing. They still freeze occasionally... The last construction site I worked on 2 winters ago, were using D8 cats, and ripping frozed ground past 8 feet deep.

@Dav4 Thanks! Thats more along what I'm looking for. I'm hoping I can keep things in the 0F and above. In reality, -30 to -40 C (-20 to -40F) are not the norm, but more like a cold snap.

@wireme I know its done, I see plants/trees wrapped in burlap, the nursery winters hundreds of trees under thick insulated tarps with next to no losses. My issue is understandint the relationship between the published zone data, and in reality what I can expect the trees to survive.

My pines and spruces, amur maple, jacks, and western larch, will all have their planters/baskets buried and sheltered. My 2 shimpaku, Alberta spruce, and elm, will be dug in as well and mulched.

Another thought. While dormant, they will be frozen (water in soil) and not growing, but will they need sunlight? If I shelter the way Im thinking, there will be no natural light.

 

[wireme]

I've seen too much debate on the light thing in the past to claim it as fact but I think they're fine without light.

 

[Bunjeh]

@PierreR Sounds like you live in a frozen hell. I would look at the surrounding flora and figure out how they survive and then recreate the environment. Snow is actually a very good insulator.

 

[Dav4]

I lived in a relatively balmy zone 6 when I started keeping bonsai, and, for 10 years, I overwintered both evergreen and deciduous trees in my garage that offered little light. All did fine. I'm in the camp that dormant trees don't need light.

 

[Cadillactaste]

If I'm not mistaken...dormant trees don't need sunlight...but will when they begin to wake up.

A concern...would be a warm winter day...that it doesn't get to warm to bring them out of dormancy. A thermometer with an alarm to go off would be a good investment I would think.

We hit -26F without wind chill last winter...can't imagine anything colder than that. Brrrrrrr

 

[M. Frary]

Once dormant the trees don't need sunlight. Or they wouldn't be dormant right?
A day or 2 above freezing won't trigger them to start growing. They are frozen solid and mulched in. It takes days before mine start to thaw under the straw.

 

[JoeR]

I think I know what I am going to do. Mind you, I am barely in zone 8a so who knows if I am any real help to you.



It was suggested to me to just keep them in an unheated building. I don't have one.


So, I have two options. I can set them on the ground and load them up with mulch and or leaves and straw. Provide wind protection.

Or I can build sort of a cold frame with cinder blocks against my house. This will keep the plants warmer just by the radiating heat of the house being contained by the blocks. Set trees in, mulch over the pots. If I need to I can easily put on or take off the top depending on the temperatures. A few people on here have threads on it if you need to see some.

 

[Cadillactaste]

Once dormant the trees don't need sunlight. Or they wouldn't be dormant right?
A day or 2 above freezing won't trigger them to start growing. They are frozen solid and mulched in. It takes days before mine start to thaw under the straw.

True...but in an enclosed area heat can build up. I open my windows on a warm day when my alarm on the thermometer goes off. Judy stressed the importance of watching those warmer winter days because of this.

 

[sorce]

Bear,

Though very spiritual, I am not religious,
However, I will pray for you!

I can't imagine any better way to help!

Your plan sounds sound, except, fully enclosed makes me think of fungus and general, wet enclosed places problems.

Sorce

 

[PierreR]

Bear,

Though very spiritual, I am not religious,
However, I will pray for you!

I can't imagine any better way to help!

Your plan sounds sound, except, fully enclosed makes me think of fungus and general, wet enclosed places problems.

Sorce

Haha!! No doubt!! We are usually drier than a popcorn fart up here, summer and winter! Last winter, I think we had one snow fall that was wet enough for the kids to make a snowman. It fell apart later that week. Fungus doesnt bother me, at least till the temps are closer to thawing. The window well has a drain to take away any actual water into the weeping tile. Thanks for the prayers brother!

 

[sorce]

No doubt

Sounds like you're keyed into what's gong on! You'll be fine!

Sorce

 

[jeanluc83]

Your plan sounds sound, except, fully enclosed makes me think of fungus and general, wet enclosed places problems.

I think the air being overly dry will be more of a problem. I overwintered my trees in an unheated garage and still lost a couple of mugo pines and junipers. Both are trees rated for much lower temperatures than my region. I was diligent with keeping them watered. My belief is that they became desiccated due to a combination of frozen roots and very dry air. This year they will be mulched in outside.

 

[M. Frary]

True...but in an enclosed area heat can build up. I open my windows on a warm day when my alarm on the thermometer goes off. Judy stressed the importance of watching those warmer winter days because of this.

Mine aren't sealed in. I have 5 that will be on my sisters porch but the porch is on the north side of the house.

 

[Cadillactaste]

Mine aren't sealed in. I have 5 that will be on my sisters porch but the porch is on the north side of the house.

If its enclosed it may pay to have a watch on the temps on a warm winters day. Judy warned me its something most overlook at times. Waking up to early from dormancy can be a threat. I know on a day that was to be overly warm...I would open the Windows early in the wee morning hours to bring temps down...close windows and counteract the heat of the day. Sometimes the windows stayed open all day. Depending on temps that were being called for and so forth.

If its an open porch you should be okay.

 

[Dav4]

I think the air being overly dry will be more of a problem. I overwintered my trees in an unheated garage and still lost a couple of mugo pines and junipers. Both are trees rated for much lower temperatures than my region. I was diligent with keeping them watered. My belief is that they became desiccated due to a combination of frozen roots and very dry air. This year they will be mulched in outside.

I never overwintered a tree, inside the garage or outside in the yard in zone 6 MA, without heavily mulching the pots and covering the soil surface with an inch or 2 right up to the trunk. Moisture from frozen soil can be slowly lost through sublimation, but a heavy layer of thoroughly moistened then frozen solid mulch will prevent this.