Vol#2 Bonsai Tree Care: How to Prepare your Bonsai Tree for Winter

Vol #2   Written by Yusuke Ogawa

Which season are you experiencing now where you live? Here in Japan, we are now in full-fledged cold winter. When you live in a cold are like this, where snow and cold temperatures are common, you need to have a special protection routine for your bonsai trees. So this is what I will explain in today’s article.

■ Why do you need to prepare your bonsai tree for winter?

During the winter, a bonsai tree can die due to being exposed to cold, dry winds. Especially when you are growing a tree vulnerable to the cold (= warm-weather tree). In these cases, it is very important to prepare for the winter season.

When looking at your garden, look at the following priority list to know which bonsais require special attention:

・ Warm-weather bonsai tree
・ Old age bonsai tree
・ Bonsais wired for winter
・ Bonsai repotted during fall

■ Let's Prepare a Muro(室-ムロ-)
Prepare a muro(室-ムロ-) or shelter to protect your bonsai trees against cold. As long as it withstands the wind and cold and keep a constant temperature and humidity, anything can serve as a muro. A vinyl greenhouse would be ideal, but it might be difficult to prepare at home, so foam Styrofoam box or a plastic box for storing your clothes will do instead.

■ Before Shelter

Do this 3 things before storing your trees.
・ Clean the tree
・ Disinfect it
・ Let it slightly cold

First, carefully clean and disinfect the bonsai before putting it in shelter. It is essential as well to keep the inside of this muro clean as it could be an excellent heat retention structure and a comfortable environment for insects and bacteria. Disinfection is very important as it reduces cause for infections Without disinfection, insects and bacteria can develop during the winter dormancy and spread their damage once when the tree gets warm. For disinfection, I recommend using lime sulfur. Diluted about 30 to 50 times for deciduous and pine trees, and between 60 to 80 times for other evergreen species.

Additionally, it is important to let the bonsai tree experience a bit of cold. If you put the tree in the shelter without exposing it to cold air at all, the tree will continue to grow, since its system will think it is still warm weather season and avoiding dormancy. The seasonal balance and growing cycle will be lost. To prevent such a situation, put the bonsai tree in the muro or shelter after exposing it to cold weather a couple of times. By understanding that "winter is coming", the tree itself will prepare for it and the winter dormancy.

■ Shelter Maintenance

・ Watering once every 3 days
・ Disinfect once a month
・ No fertilizer required
・ Don’t wire!

Once you put your bonsai in the shelter, do not touch it too much. Do only basic tasks such as watering and disinfection.

■ Storing and Taking Out Your Bonsai

Generally, when the daytime temperature drops below 5 degrees Celsius for a week, it's time to store your trees. As said earlier, it is necessary for them to experience a bit of cold for some time before storing them in your shelter structure or muro so they feel the arrival of winter. You do not have to rush to store your bonsais just because it has frosted or snowed once.

The time to take your bonsai trees from the shelter is before the buds start to grow. In Japan, it is from late March to early April since there is no need to worry about a late frost in that period. Instead of suddenly returning to their normal place and routine, let's first expose it to the outside air only during the day and gradually get used to the cold air at night.

■ Overcoming A Harsh Winter

With proper preparation, any bonsai can survive the winter. Let's welcome the warm spring together and give the bonsai growing away from their original weather a place where they can overcome the winter with tranquility.

Mr. Ogawa (owner of reBonsai, collaborator of Wazakura Japan)