Wintering Trees in Minnesota

I have a good number of trees for a new Bonsai enthusiast (10) and I realize that I will have a hard time wintering them in MN. The temperature where I live can be aorund -10 on average, and I was wondering how I would go about wintering these trees.

Details:
-I live in Zone 4. I know, it's hard to grow stuff up here.
-I have both a garage and window well, if either of those would help.
-The house does have a significant temperature drop during winter, from around 70-100 degrees in summer, so 60-75 degrees in winter. I have adequate lighting for my indoor plants, and could I weather them in my house/closet? (Closet has no heating vents and has an external wall, so it is colder than the rest of the house.)

Your best bet. Find an experienced grower of bonsai in or near your area and do what he does.

Much depends on the trees you are currently growing. Trees hardy to zone 4 can/should be kept outside in a protected spot and may only need their pots mulched with wood chips. Less hardy trees will need more protection.

Your best alternative is the garage. Do not try to winter outdoor trees in the house, least of all a closet, where they will die of mold.
Many of us in Zones 4 to 6 use the garage. Is yours insulated? You need to get a maximum-minimum thermometer. Try not to let your trees go below 25 F. It is OK if the pot freezes. Use frostproof pots.
Leave your trees outdoors until night temperatures go down to 25. My guess is that for you it will be the beginning of November. Remove all deciduous leaves, dead twigs, weeds, and moss. If there is a danger of rodents, you will have to pack them in hardware cloth. For added protection, store the trees in cartons, buried in Styrofoam peanuts up to their knees. Store them next to the inside wall. By using the maximum-minimum thermometer, you can calculate when it is likely to go below 25 in the garage. When the weather forecast is too severe, just bring the trees indoors overnight & put them back out in the morning. If you find this happening too often, you will need more insulated storage, like an old refrigerator or freezer.
Ordinary garages heat up when the sun is out in March & April. It is tricky to avoid premature leafing out. Sometimes in the spring there are a few weeks when you have to put certain trees outdoors during the day & bring them in at night.
Iris

theroc wrote:I have a good number of trees for a new Bonsai enthusiast(10)

Excellent. We need some young people on here.

There has been some good advice given thusfar but the best will come when you can tell us what kind of trees are in your beginning collection. Some may only need minimal protection while others may require something more substantial. Without knowing the plant material in question, it's rather difficult to give general advise and be certain of a succesfull outcome.

Randy

Tell us your holdings!!!!!!!!

I have a White Pine, Mugo Pine, Austrian Pine, Norway Maple, Azalea, White Oak, and two Sumac, a Buck-thorn, and as Raspberry that I'm experimenting with. I'm considering getting some other varieties of Pine later, but I want to make sure I can keep them alive through the winter.

EDIT: They're all plants that do well in this area normally, and all are either nursery stock or yamadori. I realize that they've probably survived more than one winter in the area already. I'm just worried about them being too cold in the pots.

Would it be sufficient to bury the pots in the ground with soil and mulch? I live in West-Central MN in the winter, and it can get down to -40F some days in there. Is there some sort of structure that I should build to keep over them? There is also a window well right outside my window. I could fill that with mulch and cover it with clear plastic, that should help. Just a little worried about ventilation.

This maybe a crazy idea but has anyone ever used heat tape for pipes wrapped around burried pot? Or in the soil around the the burried pots?

Heat tape would probably keep them too warm. You want them a little below freezing, but not too much, and hopefully not too much fluctuation. The ideal range is 25 to 40 F for trees whose natural habitat is Zones 3 to 7.
Iris

bonsaisr wrote:Heat tape would probably keep them too warm. You want them a little below freezing, but not too much, and hopefully not too much fluctuation. The ideal range is 25 to 40 F for trees whose natural habitat is Zones 3 to 7.
Iris

Iris is quite right on the temperature range that you want to keep the trees at. I would keep the azalea above freezing at the higher end of her temp range. A cold garage or a cold mudroom would be ideal.
Randy

I have been worried about over wintering here in Zone 6. It is my first winter with my bonsai: a chinese elm, two azaleas, an olive and a barberry.

Thanks Iris for your very helpful advice re: overwintering in an unheated the garage!

I have two questions:

1) what is hardware cloth? burlap?

2) I use the chopstick method for watering. Should I continue this method as long as plants are above freezing?

Thanks again for your help!

David.

Hello theroc,

I live in Minnesota and have been a member of the Minnesota Bonsai Society which publishes a monthly newsletter. Here is the latest newsletter:

www.minnesotabonsaisociety.org

This is the Oct. 2011 newsletter. Click on (past issues) and go to Sept.2011. Click on the (image gallery). and you will see a visual display of various ways to winter your bonsai.

Good luck and feel free to visit our club with monthly meeting on the first Tuesday of the month in St.Paul. Directions are published in the newsletter.

Norma

bonsaisr wrote:Your best alternative is the garage. Do not try to winter outdoor trees in the house, least of all a closet, where they will die of mold.
Many of us in Zones 4 to 6 use the garage. Is yours insulated? You need to get a maximum-minimum thermometer. Try not to let your trees go below 25 F. It is OK if the pot freezes. Use frostproof pots.
Leave your trees outdoors until night temperatures go down to 25. My guess is that for you it will be the beginning of November. Remove all deciduous leaves, dead twigs, weeds, and moss. If there is a danger of rodents, you will have to pack them in hardware cloth. For added protection, store the trees in cartons, buried in Styrofoam peanuts up to their knees. Store them next to the inside wall. By using the maximum-minimum thermometer, you can calculate when it is likely to go below 25 in the garage. When the weather forecast is too severe, just bring the trees indoors overnight & put them back out in the morning. If you find this happening too often, you will need more insulated storage, like an old refrigerator or freezer.
Ordinary garages heat up when the sun is out in March & April. It is tricky to avoid premature leafing out. Sometimes in the spring there are a few weeks when you have to put certain trees outdoors during the day & bring them in at night.
Iris

I am under the impression that repeated freeze and thaw of the rootmass is what creates problems, not being frozen. The insulation or mulch around the pot (or the buried pot) is to keep the root ball frozen, not to keep it from freezing. I dont even cover mine with mulch until after the first good freeze. It moderates the temps so that if the air warms a bit over freezing the roots stay frozen. This is why overwintering is better done in the shade than the sun. I have had my collection on the north side of the house, pots on or in the ground, with pine needle mulch and 4-sided wind protection but open to the sky to gather moisture from rain and snow. Been this way for as long as I have been into bonsai and generally it is without incident. The 2 dozen or so trees that I have in the ground (no pots) are not in the shade, but still come thru the winter unscathed. This has worked for me for well over a decade in Maryland.