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Wild trees in the Balkans can experience temperatures that can drop below -15 °C in winter. Usually, their roots are too deep underground to freeze. Bonsai, which are planted in shallow containers, need additional protection in winter. There are several things you can do to help your Bonsai through the colder months:

1. Do not use pots with an internal inward taper. These can have a problem if the planting medium freezes and stops the medium from expanding upwards and can lead to cracked bots.
2. Move your pots to a more sheltered, less exposed position.
3. Insulate the pots with Bubble Wrap (leave an opening for drainage).
4. Cover your trees in fleece.

And for ‘indoor Bonsai’

Here we are, deep into winter and a new year full of hope and expectations. Now is the time to protect your less hardy trees, (almost all tropical trees fall into this group), reflect on last year, what grew well and what did not? and prepare for the coming spring. Some trees need a little bit of extra care over the winter months.

Trees that should be brought inside:

• Chinese Elm
• Chinese Privet
• Fig
• Ficus
• Dwarf Umbrella Tree
• Dwarf Jade
• Azalea
• Fukien Tea

A bright, south-facing windowsill away from direct heat (e.g. on top of a heater of any kind) will keep them happy and healthy as long as you remember to keep the soil moist.

Top tips for the cold dark days of winter:

• Avoid wind. The wind is the most dangerous element in winter as cold air can dry out trees quickly. Trees that dry out in winter are more likely to lose branches or die than trees that are sheltered from the wind.
• Keep trees well-watered. Dormant trees don’t completely shut down in winter. As such, they will continue to need water. Trees in warmer and brighter spots may need watering up to once a week; in cooler spots, watering once a month might be appropriate.
• Reduce temperature fluctuations. For most temperate species, the goal is to
  maintain temperatures between 33 and 40 degrees F throughout winter. This is cold enough to meet dormancy requirements without exposing trees to harmful
  temperatures.
• Reduce freeze-thaw cycles. Trees that freeze and thaw frequently experience more stress than trees that consistently stay just above or just below freezing.
• Maintain dormancy for as long as possible. As we’ll cover below, spring care can be challenging in cold climates as late freezes can damage new growth. By keeping trees dormant until freezes become infrequent, you can help your trees grow successfully in spring.

With these criteria in mind, here are some notes about popular approaches to winter storage for bonsai.

• Place trees under benches. If your winters are relatively mild but temperatures can drop into the 20s (F), placing trees on the ground or under benches can provide additional warmth and shelter trees from heavy snow loads.
• Bury trees in the garden. By digging holes big enough for bonsai pots and
  backfilling them with dirt just over the lip of the pot, you can provide insulation for the roots while exposing the tops of trees to the elements. Shovelling snow around the trees up to the first branches can provide additional insulation.
• Place trees in covered or uncovered mulch beds. As an alternative to burying them.

Perhaps the most important thing to remember as always is to remember to talk to
your tree/s on a daily basis. Do not forget them even if they have entered into a deep
‘winter sleep’! They can still tell you how they are doing, you only have to listen!

Happy New Bonsai Year
from Balkan Bonsai