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I live in southern Sweden, where temperatures can get down to around 20C / 4F in the winter. Any tree grown outdoors is exposed to quite a lot of darkness and cold from around early November to late March. It's from this environment I've taken an acorn that have now grown indoors to a small oak tree for almost a year. The goal is to make a bonsai out of my baby oak, but I'm not sure if I should make it an indoor or outdoor bonsai.

My question is basically; Would an oak from a northern climate thrive if kept indoors through the winter, or should I leave it outside?

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it depends on the species, but assuming it is a temperate species, it may need a dormant period. – Grady Player Sep 15 '12 at 16:55
up vote 1 down vote accepted

I live where it can get as low as -40 degrees Celsius and successfully overwintered some bonsai burr oak (Quercus macrocarpa) that were eight inches tall.

Whether seedlings need to overwinter outside depends on the species. Maples and oaks growing in colder climates require a period of cold dormancy. It doesn't have to be very cold or more than four to six weeks but it is necessary to initiate leaf drop, the formation of new buds and flowering.

Other suggestions I have seen included placing the plants in a steamer trunk filled with insulation like Styrofoam peanuts but what worked for me was very simple:

  • dig a trench in soft garden soil the depth of the plant and pot.
  • place the bonsai in the ground and back fill
  • mark the location and wait for spring

I found that after a bit of cleaning up even moss growing on the surface of the pot was quite happy.

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Thanks for your answer, I will make sure to give it a dormancy period by leaving it outside. I'm living in the city, so digging a trench is not an option, but perhaps wrapping it in some kind if isolating material would provide some nice protection. – Henrik Sep 17 '12 at 18:52

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