Overwintering and soil

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From my understanding it is best to have soil with good drainage to overwinter your trees. I live in zone 5b so it gets really cold here. I have several trees that I've gotten from nurseries that are in black soil and a couple of baldies in muck. Im somewhat concerned about the amount of water they hold. Its obviously to late in the year to get them in proper bonsai soil. Does anyone have any recommendations? I was wondering if it would be beneficial to poke some small diameter holes in the soil to help improve drainage a little bit? Any suggestions or advice would be appreciated.
 

sorce

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I believe that soil has more potential to harm a pot than a tree.

So as long as you don't mind a split nursery pot it's ok.

If they're in antiques, Welcome to Crazy!

Poking holes will also help give soil somewhere to expand to when it freezes.

Sorce
 

Leo in N E Illinois

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I'm in zone 5b, north of Chicago, south of Milwaukee. I found bald cypress in pots need some protection from winter cold. Bald cypress are perfectly hardy in the ground. If I were you I would at least heal in the pots for the winter. That means, bury the pots of the trees in the ground, mulch over at least a couple inches. Or if you have an unheated garage, or a cold frame, or a window well. I use a well house to winter marginally hardy trees. Trees in nursery soils should be fine, as these nursery soils, though they hold a lot of water, are usually pretty coarse and open, usually based on composted bark.

I would NOT do any repotting at this time. For many years I would dig a trench on the north side of my house, line up the bonsai trees in the trench. Then fill the trench back in, lifting each tree so that the top rim of the pot is level or just a little below the soil level after I have filled the trench. Then a thin layer of an inch or two of leaves and then leave them alone until spring. Fine ceramic pots did not always survive this process. But plastic, mica & sturdy high fired ceramics came though this treatment just fine, as did the trees. I usually did not fill in the trench until after a few frosts. so I did not have much trouble with vermin eating the bark of the trees. Though my neighborhood always has a surplus of feral house cats, so mice and rabbits are not an issue.

Individual trees have different temperature to which their roots are hardy. The above ground part of the tree are hardy to one temperature, the roots are hardy to a different temperature. The ground stays significantly warmer than the air. In zone 5b your coldest average nighttime winter temperature will be -15 F or -26 C. If you measure temperature at 4 inches below the soil, roughly 10 cm below soil, your temperature may be as warm as +10 F, or -12 C. This is 25 degree F warmer ( 13 C warmer) than the ambient air temperature. Soil is an excellent insulator, and there is constant heat rising from beneath the earth. So healing in pots is quite effective. A cold frame is usually sunk below grade, so the bulk of its volume is underground, this is to get the heat from the soil. IF you use a cold frame. For most of the winter keep it covered with a layer of insulation, styrofoam wall board or other material. Glass does not keep the cold out as well as is needed for zone 5b winters.

Michael Hagedorn in his book "Bonsai Heresy" has a table that he uses which lists temperatures to which roots are hardy for a number of species of bonsai trees. The table was developed for the landscape industry. Because of copyright concerns I won't publish the table here, you really should buy the book, there are many excellent tips in there. It is well worth the $25 list price, and Stone Lantern often has deals, you might find it for less. As a result of his book I have begun to re-think my habit of wintering certain trees by just setting their pots on the ground, without any protection beyond that.

I have had success just setting pots of the ground of some trees in zone 5b. For example, eastern hemlock, Tsuga canadensis, all my spruce, Picea, and Pinus strobus, sylvestris, mugo, and P. ponderosa, all just get set on the ground. Also junipers. But I do protect by moving to my well house, azalea, bald cypress, ginkgo, and many other less root hardy species.
 
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Cosmos

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Michael Hagedorn in his book "Bonsai Heresy" has a table that he uses which lists temperatures to which roots are hardy for a number of species of bonsai trees. The table was developed for the landscape industry. Because of copyright concerns I won't publish the table here, you really should buy the book, there are many excellent tips in there. It is well worth the $25 list price, and Stone Lantern often has deals, you might find it for less. As a result of his book I have begun to re-think my habit of wintering certain trees by just setting their pots on the ground, without any protection beyond that.

I have had success just setting pots of the ground of some trees in zone 5b. For example, eastern hemlock, Tsuga canadensis, all my spruce, Picea, and Pinus strobus, sylvestris, mugo, and P. ponderosa, all just get set on the ground. Also junipers. But I do protect by moving to my well house, azalea, bald cypress, ginkgo, and many other less root hardy species.

*Sorry if I’m hijacking the thread a bit there*

Hi Leo, I have read Hagedorn’s book recently, and this chapter especially caught my eye as it seemed to contradict our experience as cold-climate bonsai growers. The table from Iseli seems to not give enough credit to how hardy a lot of species are. I’ve had spruce, larch, mugos, survive lows of -25 celcius simply mulched on my south-facing 3rd-floor balcony, albeit these were all raw or early stage bonsai.

In what ways did the book make you reconsider your own ways of overwintering trees? I’m asking myself these questions. I wonder if trees in bonsai cultivation aren’t hardier than your average nursery production tree because of "optimal" growing conditions and fertilization.
 

Leo in N E Illinois

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*Sorry if I’m hijacking the thread a bit there*

Hi Leo, I have read Hagedorn’s book recently, and this chapter especially caught my eye as it seemed to contradict our experience as cold-climate bonsai growers. The table from Iseli seems to not give enough credit to how hardy a lot of species are. I’ve had spruce, larch, mugos, survive lows of -25 celcius simply mulched on my south-facing 3rd-floor balcony, albeit these were all raw or early stage bonsai.

In what ways did the book make you reconsider your own ways of overwintering trees? I’m asking myself these questions. I wonder if trees in bonsai cultivation aren’t hardier than your average nursery production tree because of "optimal" growing conditions and fertilization.

I was struck by how different the hardiness was for the above ground portion of the tree and how much less hardy the roots were reported to be.

His table is "unpublished". He states some of the values were from experiments done at OSU, and some of the values are from Iseli Nursery. He says the data from Iseli may be more conservative (warmer) than the data from OSU. The problem is, he does not identify which value was from which source. I've had trouble with Ginkgo not surviving being set on the ground for the winter, and the value of +15 F being the lower limit for root hardiness could actually explain why I was having mortalities with wintering ginkgo. I switched to wintering ginkgo in my well house, and have had no further winter losses.

However, you are right, Picea pungens, blue spruce, I've left out in very exposed locations through -15 F and have had no losses, yet the table lists +9 F as the lower limit. Hagedorn is in the fairly mild Pacific Northwest, I believe he has said at his nursery he has not had temps below +9 F. Some of the numbers may simply be that neither Hagadorn or Iseli have had the cold to test certain species below +9 F.

I'm still re-reading the chapter, I have not completely digested what is in the chapter. I'm not sure I will change what I do. But I am rethinking the issue. I think mulching in might be preferable over just setting the hardies on the ground. It will probably be a year or two before I can talk coherently about what changes, if any I will make or might not make. The book is certainly food for thought.
 

JudyB

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If they are still in nursery soil, why don't you do what all the nurseries do for wintering? They just heel them in- in either mulch or dirt. As long as they are hardy to your area, I don't see the advantage to protecting these like you would a bonsai or bonsai in training.
 
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I'm in zone 5b, north of Chicago, south of Milwaukee. I found bald cypress in pots need some protection from winter cold. Bald cypress are perfectly hardy in the ground. If I were you I would at least heal in the pots for the winter. That means, bury the pots of the trees in the ground, mulch over at least a couple inches. Or if you have an unheated garage, or a cold frame, or a window well. I use a well house to winter marginally hardy trees. Trees in nursery soils should be fine, as these nursery soils, though they hold a lot of water, are usually pretty coarse and open, usually based on composted bark.

I would NOT do any repotting at this time. For many years I would dig a trench on the north side of my house, line up the bonsai trees in the trench. Then fill the trench back in, lifting each tree so that the top rim of the pot is level or just a little below the soil level after I have filled the trench. Then a thin layer of an inch or two of leaves and then leave them alone until spring. Fine ceramic pots did not always survive this process. But plastic, mica & sturdy high fired ceramics came though this treatment just fine, as did the trees. I usually did not fill in the trench until after a few frosts. so I did not have much trouble with vermin eating the bark of the trees. Though my neighborhood always has a surplus of feral house cats, so mice and rabbits are not an issue.

Individual trees have different temperature to which their roots are hardy. The above ground part of the tree are hardy to one temperature, the roots are hardy to a different temperature. The ground stays significantly warmer than the air. In zone 5b your coldest average nighttime winter temperature will be -15 F or -26 C. If you measure temperature at 4 inches below the soil, roughly 10 cm below soil, your temperature may be as warm as +10 F, or -12 C. This is 25 degree F warmer ( 13 C warmer) than the ambient air temperature. Soil is an excellent insulator, and there is constant heat rising from beneath the earth. So healing in pots is quite effective. A cold frame is usually sunk below grade, so the bulk of its volume is underground, this is to get the heat from the soil. IF you use a cold frame. For most of the winter keep it covered with a layer of insulation, styrofoam wall board or other material. Glass does not keep the cold out as well as is needed for zone 5b winters.

Michael Hagedorn in his book "Bonsai Heresy" has a table that he uses which lists temperatures to which roots are hardy for a number of species of bonsai trees. The table was developed for the landscape industry. Because of copyright concerns I won't publish the table here, you really should buy the book, there are many excellent tips in there. It is well worth the $25 list price, and Stone Lantern often has deals, you might find it for less. As a result of his book I have begun to re-think my habit of wintering certain trees by just setting their pots on the ground, without any protection beyond that.

I have had success just setting pots of the ground of some trees in zone 5b. For example, eastern hemlock, Tsuga canadensis, all my spruce, Picea, and Pinus strobus, sylvestris, mugo, and P. ponderosa, all just get set on the ground. Also junipers. But I do protect by moving to my well house, azalea, bald cypress, ginkgo, and many other less root hardy species.
That was a lot of really helpful information. I will definitely be checking out that book. Thanks
 
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I'm in zone 5b, north of Chicago, south of Milwaukee. I found bald cypress in pots need some protection from winter cold. Bald cypress are perfectly hardy in the ground. If I were you I would at least heal in the pots for the winter. That means, bury the pots of the trees in the ground, mulch over at least a couple inches. Or if you have an unheated garage, or a cold frame, or a window well. I use a well house to winter marginally hardy trees. Trees in nursery soils should be fine, as these nursery soils, though they hold a lot of water, are usually pretty coarse and open, usually based on composted bark.

I would NOT do any repotting at this time. For many years I would dig a trench on the north side of my house, line up the bonsai trees in the trench. Then fill the trench back in, lifting each tree so that the top rim of the pot is level or just a little below the soil level after I have filled the trench. Then a thin layer of an inch or two of leaves and then leave them alone until spring. Fine ceramic pots did not always survive this process. But plastic, mica & sturdy high fired ceramics came though this treatment just fine, as did the trees. I usually did not fill in the trench until after a few frosts. so I did not have much trouble with vermin eating the bark of the trees. Though my neighborhood always has a surplus of feral house cats, so mice and rabbits are not an issue.

Individual trees have different temperature to which their roots are hardy. The above ground part of the tree are hardy to one temperature, the roots are hardy to a different temperature. The ground stays significantly warmer than the air. In zone 5b your coldest average nighttime winter temperature will be -15 F or -26 C. If you measure temperature at 4 inches below the soil, roughly 10 cm below soil, your temperature may be as warm as +10 F, or -12 C. This is 25 degree F warmer ( 13 C warmer) than the ambient air temperature. Soil is an excellent insulator, and there is constant heat rising from beneath the earth. So healing in pots is quite effective. A cold frame is usually sunk below grade, so the bulk of its volume is underground, this is to get the heat from the soil. IF you use a cold frame. For most of the winter keep it covered with a layer of insulation, styrofoam wall board or other material. Glass does not keep the cold out as well as is needed for zone 5b winters.

Michael Hagedorn in his book "Bonsai Heresy" has a table that he uses which lists temperatures to which roots are hardy for a number of species of bonsai trees. The table was developed for the landscape industry. Because of copyright concerns I won't publish the table here, you really should buy the book, there are many excellent tips in there. It is well worth the $25 list price, and Stone Lantern often has deals, you might find it for less. As a result of his book I have begun to re-think my habit of wintering certain trees by just setting their pots on the ground, without any protection beyond that.

I have had success just setting pots of the ground of some trees in zone 5b. For example, eastern hemlock, Tsuga canadensis, all my spruce, Picea, and Pinus strobus, sylvestris, mugo, and P. ponderosa, all just get set on the ground. Also junipers. But I do protect by moving to my well house, azalea, bald cypress, ginkgo, and many other less root hardy species.
Right now I have all of my junipers, american elm, and amur maple buried up to the first branch in mulch, so I think they are good. Im still debating what to do with my baldies, chinese elm, and one trident maple. I have an unheated garage with no insulation which will provide minimal cold protection. I have thought about building a heatbed or cold frame in my garage for them. My other thought was just burying them also which would protect them from the temp fluctuations we get here frequently in fall and spring (70 one week, 5 the next lol). Im sure I'm probably putting too much thought into it. Im rather uninformed when it comes to well houses so I'm wondering how yours would compare to my garage for protection. Any thoughts? Again, thanks for the help.
 

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