Overwintering Evergreens

[JonW]

I can't find a definitive answer regarding overwintering evergreen trees. It's about 50/50 whether sources say they need light over winter.

I have a nice size collection of tropicals, and ended up with a few cold-hardy deciduous plants that I overwinter under my storm doors. But I'm considering getting some evergreen and/or coniferous trees. I don't have a place to heel in, and the area under my storm doors barely gets any light. I have a disconnected garage, but not much space and not sure I want to commit to water plants in my garage for years to come (even though its like monthly watering).

I am interested in a boxwood (I posted a thread about this, sorry for the redundancy), azalea and I have a juniper (precumbens nana) that I put back into the ground (it was a regifted big-box store bonsai). Alternatively, I could expand my tropical or deciduous collection. I'm air-layering a maple and one of my crepe myrtle, and might buy another maple, a larch or redwood/cypress.

Has anyone here had success, year after year, overwintering evergreens (broadleaf and conifer) in a cold space WITHOUT light? If not, anything that would survive outdoors without heeling in?

 

[RKatzin]

My winter storage area is the size of a two car garage attached to the north side of the house. The roof above is a deck and the two sides are cinder block walls. The front is open to the north. It's cold and dark under there.
I stack my deciduous trees on three shelves all the in back up against the house. Then there's three full length benches with deciduous trees too tall for the back shelves on the first. Then evergreen and conifers on the outermost two benches.
I do this not because the conifers need light, but because they are the most resilient to the winter weather effects and provide a windbreak for the more sensitive deciduous trees.
I used to winter all my trees right where they sat with no protection at all. Never lost one to winter weather, but did see some damage on the finer twigs of the deciduous trees from wind burn and broken branches on conifers and deciduous trees. I stacked over 200 trees in there with no damages, except a little nibbling on new buds by some mice, which I took care of with some peanut butter snappers.

 

[sorce]

Welcome to Crazy!

I had a Juniper and a Boxwood both get healthier over this past winter.
That wouldn't have happened without light, worse, in an enclosed space without attention to temperature and humidity.

Oh, both those trees are in less than 4 cubic inches of soil and get left just on the ground.
Through some of the worst winter weather for bonsai imaginable.

Where are you?

Sorce

 

[Vali]

Through some of the worst winter weather for bonsai imaginable.

How low do the temperatures go in your area in wintertime? Aproximately...

 

[sorce]

How low do the temperatures go in your area in wintertime? Aproximately...

A record of freeze thaw cycles is the most telling, more damaging. I think we suck there worse.



Sorce

 

[Leo in N E Illinois]

@JonW - put your location into your profile. Go to upper menu bar of the forum. On the right hand side, click or double click on your screen name to open your profile. You can edit your profile from there. Put a general location in, if you live in a tiny town nobody heard of, the nearest big city or just the state location will do. Always include your state, every state in USA has a Springfield.
Then others will be able to give you location relevant advise.

For example, your current question. We need to know where you live to be able to suggest good candidates for the "leave 'em lay" method of overwintering you bonsai.

I am in the same climate as @sorce, who posted above. There are a number of trees I simply set on the ground for winter, or leave them right where they grew all summer. I am considered to be in zone 5b. The leave them out and exposed works well with trees that are native to your own area and areas that are colder than your own area. For example, in my yard I have
Malus - flowering crab apple
Amelanchier - Serviceberry, or Juneberry or Saskatoon or any of a dozen common names - pretty white flowers before leaves open.
Cotoneaster - white flowers and small red fruit
Metasequoia - dawn redwood
Pinus banksiana - Jack pine
Pinus mugo - Mugo pine
Pinus sylvestris - Scotts pine
Tsuga canadensis - eastern hemlock
Chamaecyparis obtusa - Hinoki - this was a surprise to me, I did not think Hinoki would do so well in my winters. But they do.
Pinus bungeana - Chinese lacebark pine - seedlings in an Anderson flat seem fine, so far 4 winters they are still hardy.
Juniper chinensis - both 'Itoigawa' and 'Kishu' cultivars are perfectly hardy
Juniper horizontalis - perfectly hardy.
Buxus sempervirens - European boxwood - this is the EU boxwood, it is wonderfully hardy, the other boxwood species may or may not be fully hardy.
Rhododendron (Azalea) 'White Lights' - some of the deciduous azalea are super hardy.
Vaccinium corymbosum - highbush blueberry - this is the blueberry that is a 5 foot tall shrub. This is not the lowbush blueberry.
Ulmus pumila - Siberian elm
Ulmus thomasii - Rock elm
Ulmus parvifolia - Chinese elm
Carpinus caroliniana, Carpinus coreana, both American and Korean hornbeams.
and a fair number more species.

So all the above have been out in my yard even through the 2019 winter where according to Sorce, we had -22 F.

One word of warning, all the above are in pots that either have shapes that allow the root ball to float as the root ball freezes and expand, or the pots are plastic which will expand. If you have bonsai trees in ceramic pots, you need to evaluate the shape and resiliency of the clay to see if they could handle the pressure of an expanding frozen root ball. Some fine pottery will do fine, my Sam Miller pots, Sara Raynor pots, and my Tokanome pots all do fine. Its been hit and miss for some others. You need to assess the shape and quality of the pot. Walls that slope inward, or perfectly straight, are much more likely to lock the root mass into the pot, Water in the soil expands as it freezes, and as it does, it can beak pottery.

Hope this helps.

 

[sorce]

I am in the same climate as @sorce,

Someone was talking recently about the severe differences in climates. About wet belts.

Anyway.

I remember when I was in your area in spring, and everything tlwas closed or just moving, the same week I was 45 minutes South, noting everything about 1 week ahead.

Recently, I thought about how extreme these differences are, since it is the beginning of the years rythym.

1 week, is putting trees on an entirely different regiment.

IMo.

The lake makes it so man can not predict the difference.

Sorce

 

[Vali]

I had a Juniper and a Boxwood both get healthier over this past winter.

How about your other evergreen trees? Do you keep them somewhere protected? That was a really low temperature, it's really good to know that some species can take that

 

[leatherback]

It's about 50/50 whether sources say they need light over winter.

Depends on how cold you store them. When frozen pretty much all processes come to an effective standstill. But when at 5c / 41f evergreens enjoy the weather.

 

[sorce]

How about your other evergreen trees? Do you keep them somewhere protected? That was a really low temperature, it's really good to know that some species can take that

They all just go on the ground, with a bit of windblock, 2ft high on any side.

Noting this year, the larger boxes, they don't like this, being wet and cold all year, I keep losing bark and trunk.

But the English box been ok so far.

I'm still working out what needs no pampering. The rest goin die!

Sorce

 

[Leo in N E Illinois]

Both on the farm in SW Michigan, zone 6a, and tends to have more snow. And in my back yard, Illinois, zone 5b. My junipers sit exactly where they grow all summer, in the sun, pot on the ground. They change color over winter, but green up nicely in spring.

 

[JonW]

Welcome to Crazy!

I had a Juniper and a Boxwood both get healthier over this past winter.
That wouldn't have happened without light, worse, in an enclosed space without attention to temperature and humidity.

Oh, both those trees are in less than 4 cubic inches of soil and get left just on the ground.
Through some of the worst winter weather for bonsai imaginable.

Where are you?

Sorce

Thanks - Pittsburgh PA. I was thinking of getting a small cold frame, but that doesn't allow air flow...

 

[JonW]

@JonW - put your location into your profile. Go to upper menu bar of the forum. On the right hand side, click or double click on your screen name to open your profile. You can edit your profile from there. Put a general location in, if you live in a tiny town nobody heard of, the nearest big city or just the state location will do. Always include your state, every state in USA has a Springfield.
Then others will be able to give you location relevant advise.

For example, your current question. We need to know where you live to be able to suggest good candidates for the "leave 'em lay" method of overwintering you bonsai.

I am in the same climate as @sorce, who posted above. There are a number of trees I simply set on the ground for winter, or leave them right where they grew all summer. I am considered to be in zone 5b. The leave them out and exposed works well with trees that are native to your own area and areas that are colder than your own area. For example, in my yard I have
Malus - flowering crab apple
Amelanchier - Serviceberry, or Juneberry or Saskatoon or any of a dozen common names - pretty white flowers before leaves open.
Cotoneaster - white flowers and small red fruit
Metasequoia - dawn redwood
Pinus banksiana - Jack pine
Pinus mugo - Mugo pine
Pinus sylvestris - Scotts pine
Tsuga canadensis - eastern hemlock
Chamaecyparis obtusa - Hinoki - this was a surprise to me, I did not think Hinoki would do so well in my winters. But they do.
Pinus bungeana - Chinese lacebark pine - seedlings in an Anderson flat seem fine, so far 4 winters they are still hardy.
Juniper chinensis - both 'Itoigawa' and 'Kishu' cultivars are perfectly hardy
Juniper horizontalis - perfectly hardy.
Buxus sempervirens - European boxwood - this is the EU boxwood, it is wonderfully hardy, the other boxwood species may or may not be fully hardy.
Rhododendron (Azalea) 'White Lights' - some of the deciduous azalea are super hardy.
Vaccinium corymbosum - highbush blueberry - this is the blueberry that is a 5 foot tall shrub. This is not the lowbush blueberry.
Ulmus pumila - Siberian elm
Ulmus thomasii - Rock elm
Ulmus parvifolia - Chinese elm
Carpinus caroliniana, Carpinus coreana, both American and Korean hornbeams.
and a fair number more species.

So all the above have been out in my yard even through the 2019 winter where according to Sorce, we had -22 F.

One word of warning, all the above are in pots that either have shapes that allow the root ball to float as the root ball freezes and expand, or the pots are plastic which will expand. If you have bonsai trees in ceramic pots, you need to evaluate the shape and resiliency of the clay to see if they could handle the pressure of an expanding frozen root ball. Some fine pottery will do fine, my Sam Miller pots, Sara Raynor pots, and my Tokanome pots all do fine. Its been hit and miss for some others. You need to assess the shape and quality of the pot. Walls that slope inward, or perfectly straight, are much more likely to lock the root mass into the pot, Water in the soil expands as it freezes, and as it does, it can beak pottery.

Hope this helps.

Thanks - that's a great list! I addedd my location - zone 6 Pittsburgh PA.

I have a Juniper Precumbens Nana planted in ground (the one that was regifted, from a big-box store). I was also thinking of getting an American Larch and Dawn Redwood or Bald Cypress - all of these are deciduous and wouldn't matter if they got light, but maybe the Bald Cypress wouldn't be cold hardy enough to just leave outside (so Redwood might be better).

I've been enjoying the fine branching on my Crepe Myrtle, which is why I'm interested in some more cold-hardy plants. I was thinking of Elm, but I always hesitate before getting one due to the reputation of having a lot of branch loss. I have an air layer on a Mikawa Yatsubusa that is planted in the ground.

Mostly, I use plastic pots. I have some ceramic, and I avoid any with an inward lip.

Should I try a cold frame? Or just leave it out? Also, I guess either way, I have to make sure it stays hydrated (or frozen).

Thanks all! I've been doing bonsai for a number of years, but almost solely tropical like various ficus, schefflera, jade, portulacaria afra, podocarpus, neaa buxifolia... Debating sticking with tropicals (but I'm just about out of indoor space in winter) or trying a range of cold-hardy plants, because I feel I'm probably missing out on those.

 

[leatherback]

I was thinking of Elm, but I always hesitate before getting one due to the reputation of having a lot of branch loss.

Odd.. Never heard of this for elm. Birch yes. Elm, no.

 

[JonW]

Odd.. Never heard of this for elm. Birch yes. Elm, no.

Particularly dwarf varieties.

So, considering my location, any consensus as to a safe overwintering plan? Is the cold frame the best option?

 

[Leo in N E Illinois]

I have had Siberian elm drop the occasional branch, usually just fine twigging, easy enough to replace, they grow quickly enough that replacement is rapid. I have not lost branches from other elms.

Most of the trees I leave out are in middle stages of development, I would hesitate to take a $5000 advanced developed elm that was raised in California or Florida and just leave it out in my backyard. But I did just "leave it where it lays" with a $200 dawn redwood planting. Now it is probably a $300 dawn redwood planting. It continues to get better.

Warning: This does not work for absolutely everything. Some trees that are perfectly hardy planted in the ground have trouble with being in a pot set on the ground. Ginkgo and Bald Cypress are perfectly hardy in the landscape in my neighborhood, but neither will survive the winter in a pot just setting on the ground. I end up moving these to my well house to protect them for winter.

The natural native range for both these species is confined to warmer regions than my location, but they are widely planted in colder areas in the landscape. This might be a clue. If a tree is native to colder areas than your location, it will probably be fine. If it is only native to warmer areas, but survives as a landscape plant, this is one that needs to be "tested" before just leaving a more developed example outside.

A cold frame would probably be a great idea for trees like ginkgo, & bald cypress. Or you could experiment with healing them in. Another in the same category as ginkgo, hardy in the landscape, not reliably hardy in a pot, Japanese black pine. Listed as zone 5 hardy, I find they will only be hardy 3 or 4 out of 5 winters. They are hardy enough they fool you. A cold frame or other protection is the way to go.

Important with winter shelters. The shelter must keep the trees cold during winter thaws. The biggest problem with garages, cold frames and sheds is if they get warm on a mild January or February day. If you build a cold frame, be certain it is insulated from heat, and that if you use any glass, it is covered with an opaque insulation that is left in place until a week or two before average last frost, so that it stays cold. Big problems, when trees wake up weeks or even months before last frost. Then you are stuck doing the "in and out" dance, and if you get distracted on evening, that freeze can really damage a tree that has committed to growing.

THe leave it on the ground method, mostly avoids this problem, as trees seldom wake up too early.

Japanese maples - this is a problem group. Acer palmatum in particular, after winter chill hours are met, will wake up at the drop of a hat. An oak or north american native elm will need two weeks of warmth above 40 F to wake up, the Japanese maple seems like it will wake up with as little as 24 or 48 hours above 40F. Even if your climate was warm enough to just leave it lay in the landscape you may end up having to do the "in and out" dance because they tend to wake up before last frost.

So it takes experimentation. Start with modest prices trees to experiment with. It does take a little trial and error to get the hang of it.

Flowering quince - Chaenomeles species and hybrids. I find the larger, more coarse growing Chaenomeles are perfectly hardy just left on the ground. The small leaved cultivars, in particular 'Chojubai', 'Hime' and 'Kan Toyo' - the dwarf growing cultivars, are not very cold hardy. Like ginkgo, they need protection. I am not certain whether they are hardy in the ground in my area or not. I know they are not hardy in a pot set on the ground. The large leaf types, like 'Contorted White'. 'Toyo Nishiki', 'Double Take Red' are all quite hardy, and do well with my system.

Healing pots into the ground or in a bed on the ground can improve success over just setting a pot on top of the ground. Due to heavy clay, this is more work than moving a tree into a well house. But if your soil is easy to work, a bed to heal pots into is a definite help.

Trees like Satsuki azalea and crepe myrtle, which are not hardy in the landscape by me do spend winters in my well house.

 

[JonW]

I have had Siberian elm drop the occasional branch, usually just fine twigging, easy enough to replace, they grow quickly enough that replacement is rapid. I have not lost branches from other elms.

Most of the trees I leave out are in middle stages of development, I would hesitate to take a $5000 advanced developed elm that was raised in California or Florida and just leave it out in my backyard. But I did just "leave it where it lays" with a $200 dawn redwood planting. Now it is probably a $300 dawn redwood planting. It continues to get better.

Warning: This does not work for absolutely everything. Some trees that are perfectly hardy planted in the ground have trouble with being in a pot set on the ground. Ginkgo and Bald Cypress are perfectly hardy in the landscape in my neighborhood, but neither will survive the winter in a pot just setting on the ground. I end up moving these to my well house to protect them for winter.

The natural native range for both these species is confined to warmer regions than my location, but they are widely planted in colder areas in the landscape. This might be a clue. If a tree is native to colder areas than your location, it will probably be fine. If it is only native to warmer areas, but survives as a landscape plant, this is one that needs to be "tested" before just leaving a more developed example outside.

A cold frame would probably be a great idea for trees like ginkgo, & bald cypress. Or you could experiment with healing them in. Another in the same category as ginkgo, hardy in the landscape, not reliably hardy in a pot, Japanese black pine. Listed as zone 5 hardy, I find they will only be hardy 3 or 4 out of 5 winters. They are hardy enough they fool you. A cold frame or other protection is the way to go.

Important with winter shelters. The shelter must keep the trees cold during winter thaws. The biggest problem with garages, cold frames and sheds is if they get warm on a mild January or February day. If you build a cold frame, be certain it is insulated from heat, and that if you use any glass, it is covered with an opaque insulation that is left in place until a week or two before average last frost, so that it stays cold. Big problems, when trees wake up weeks or even months before last frost. Then you are stuck doing the "in and out" dance, and if you get distracted on evening, that freeze can really damage a tree that has committed to growing.

THe leave it on the ground method, mostly avoids this problem, as trees seldom wake up too early.

Japanese maples - this is a problem group. Acer palmatum in particular, after winter chill hours are met, will wake up at the drop of a hat. An oak or north american native elm will need two weeks of warmth above 40 F to wake up, the Japanese maple seems like it will wake up with as little as 24 or 48 hours above 40F. Even if your climate was warm enough to just leave it lay in the landscape you may end up having to do the "in and out" dance because they tend to wake up before last frost.

So it takes experimentation. Start with modest prices trees to experiment with. It does take a little trial and error to get the hang of it.

Flowering quince - Chaenomeles species and hybrids. I find the larger, more coarse growing Chaenomeles are perfectly hardy just left on the ground. The small leaved cultivars, in particular 'Chojubai', 'Hime' and 'Kan Toyo' - the dwarf growing cultivars, are not very cold hardy. Like ginkgo, they need protection. I am not certain whether they are hardy in the ground in my area or not. I know they are not hardy in a pot set on the ground. The large leaf types, like 'Contorted White'. 'Toyo Nishiki', 'Double Take Red' are all quite hardy, and do well with my system.

Healing pots into the ground or in a bed on the ground can improve success over just setting a pot on top of the ground. Due to heavy clay, this is more work than moving a tree into a well house. But if your soil is easy to work, a bed to heal pots into is a definite help.

Trees like Satsuki azalea and crepe myrtle, which are not hardy in the landscape by me do spend winters in my well house.

Thanks so much! I really appreciate the detailed response - very knowledgeable. However, it seems your info left me with more questions (sorry!):

Do you have a suggestion specifically for boxwood (either English or Kingsville)? It sounds like some folks leave them out, but maybe a cold-frame would be best?

Is there a variety of elm that is hard, with small leaves I should try? Maybe Larch and or Redwood would be good options. Or is there something else you'd start with? I'm looking for plants that are rewarding to work with, but not challenging to keep alive.

Assuming my air-layer works, I was planning on keeping the maple under my storm doors, but there is probably a good chance it would wake early. But I'm assuming it's not cold hardy enough to be left on the ground.

For the cold frame, I'd probably take the plants out when we get past the worst of the winter. We only have a few months with really cold weather - by the end of March or April, we might get snow, but it rarely is cold enough to sit on the ground. I was thinking I would transition some plants out of a cold frame and move some of the hardier tropicals into the cold frame.

How does your well house differ from a cold frame? Is there light (I'm assuming your Azalea needs light over winter)?

 

[Leo in N E Illinois]

My well house is a subterranean room, under the patio in the back yard. Access is through a 4 foot high door through the foundation of the house. What looks like a patio in the back yard is the roof of the well house. One of the very few benefits of living in a 100 year old farm house. When the house was added to the municipal water system, the pump & pressure tank were removed from the well house, and concrete was poured to plug the well bore. This is not a typical accessory to a modern house. The room keeps the temperature of the soil. It is totally dark. No windows. I run an extension cord to power a fan that I leave on 24/7 to keep air moving, otherwise due to the dampness of the room, I get rots in the winter. Air moving and it is perfect. It stays below 40 F most of the winter. Because of this I do not need light. The only light in the well house is a ordinary bulb I turn on only when I go in to water or look around. The floor of the well house is roughly 56 inches below ground. This is much deeper than a cold frame normally would be. Also, there is no opening to the outside, access is only through the door through the foundation wall in the basement. There is no outside light.

Evergreens, like Japanese black pine & Satsuki azaleas, do not need light in winter if the temperatures are below 40 F, or 4 C. The well house stays between 32 F and 40 F. (0 C to +4 C). This is a very narrow range. As the ground warms in spring, the well house does slowly creep up in temperature, and I do get some growth on trees that are quick to wake up. Fortunately, Satsuki seem to stay dormant until about 45 F or so, so they stay dormant through the last week leading to time to put outdoors. When I see landscape trees leafing out, then it is time to empty the well house. When leaves of Norway and Freeman maples in my landscape are half way expanded, when trees are starting to cast shade again, then the well house gets emptied. I also check weather forecasts. But landscape trees are a good guide.

 

[Leo in N E Illinois]

I have English boxwood, Buxus sempervirens, which I leave out no problem. It is probably hardy through all of zone 5.

When buying boxwood, often the labels do not tell you which species of boxwood the variety you are buying belongs to. I can guarantee that Buxus sempervirens is fully winter hardy in zone 5b. I can not vouch for the other species and or varieties of other species are winter hardy. 'Kingsville' boxwood I believe is not from the English boxwood species, and therefore would not be winter hardy.

IF you see a boxwood being sold at your local landscape nursery for use as a hedge, that would likely be one of the cold tolerant species. Boxwood sold as bonsai can be from one of the more subtropical species or sometimes from one of the hardy ones. Buying boxwood from a bonsai nursery require that you do the extra leg work to find out which species it is before you can guess at its hardiness., because so many boxwoods are sold as "indoor bonsai".

 

[JonW]

I have English boxwood, Buxus sempervirens, which I leave out no problem. It is probably hardy through all of zone 5.

When buying boxwood, often the labels do not tell you which species of boxwood the variety you are buying belongs to. I can guarantee that Buxus sempervirens is fully winter hardy in zone 5b. I can not vouch for the other species and or varieties of other species are winter hardy. 'Kingsville' boxwood I believe is not from the English boxwood species, and therefore would not be winter hardy.

IF you see a boxwood being sold at your local landscape nursery for use as a hedge, that would likely be one of the cold tolerant species. Boxwood sold as bonsai can be from one of the more subtropical species or sometimes from one of the hardy ones. Buying boxwood from a bonsai nursery require that you do the extra leg work to find out which species it is before you can guess at its hardiness., because so many boxwoods are sold as "indoor bonsai".

Ok - thank you. I think Kingsville is a Microphylla/Japanese Boxwood. They are hardy to zone 5. I was thinking of putting it in a polycarbinate frame with maybe some ventilation on my front porch, which would offer a bit more protection from swings in temperature. I have Korean Boxwoods on my property (Buxus Sinica), which are very cold hard and vigorous, but they have slightly larger leaves, so it seems people rarely use them for bonsai. English typically seems to have smaller, longer leaves. I believe there are some hybrid English/Korean cultivars that have the leaf size of English and vigor of Korean, and are cold hardy, but I don't recall.