Winter has settled for a few days with temperatures dropping below zero. Down to – 5 C / 23 °F. This lasts for another week, so we have to freeze for two weeks in a row.

What freezing does to our bonsai

Low temperatures are not bad for bonsai, because it helps them go into dormancy. What is extremely important. Trees have different tolerances of how much freezing, and for how long, they tolerate.

The Japanese white pine thrive well in cold weather for some time.

Trident maples don’t like these temperatures, so they are stored safely when temperatures drop like this. Japanese maples are more tolerant, so you must know your species and what they cope with.

It isn’t so much the branches that may be damaged by severe cold, but much more roots that are fragile. roots are normally buried in the ground in nature or in the garden, and temperatures are much higher there. Therefore many trees dislike roots getting cold, whereas branches are designed to manage it.

Shohin bonsai are stored and protected from frosts.

A complex system of sugars is constantly changing from being growth developing to frost protection as temperatures shifts. This isn’t taking place the same way, or as effectively, in the root system. And, as bonsai are grown in pots they are more vulnerable and exposed to the cold being above ground getting the full impact from cold winds.

It’s more the roots that will be harmed from severe freezing, and not so much the branches.

Overwintering

Large bonsai can be placed on the ground outside, giving them some heat from the ground, or at least not being cooled as offensive as when sitting in free air circulation on benches lifted from the ground.

Juniperus chinensis still getting some cold outside.

Small Shohin is even more vulnerable. Taking into consideration the small pots and limited amount of roots. After a few days of light freezing, I bring them into the storage room. They need that bite of frost first to go fully into dormancy, and then they are protected from severe cold. Ideally stored in a place where temperatures are just above freezing, allowing the roots to take up water.

Winter may change soon again, and we will be back to the new normal. Wet and cloudy. I prefer the clear sunny cold winters, and so do trees. Wet weather makes fungi thrive, whereas cold weather kills bugs and cleans up the air.

Be sure to check often if your bonsai needs water. In winter they will still loose water from the soil, and might dry out.