Keeping your bonsai alive through a cold winter season is one of the most nerve-racking experiences for a bonsai novice. You’re probably asking yourself “how do I overwinter bonsai?” or “what happens if it snows?” If you live in a temperate climate that experiences cold winters, learning how to overwinter bonsai is critical.
It’s a common misconception that most bonsai trees can survive indoors. In reality, most species used for bonsai, including many deciduous trees, like elms and maples, and conifers, like junipers and pines, are outdoor trees. These trees come from temperate environments that experience both warm summers and cold winters.
In the fall, you’ll notice that your trees begin to change. Growth will slow to a halt, and the soft growth on woody trees from the spring will harden. This transformation is all part of the natural cycle that your tree goes through in preparation for its winter rest. This period of dormancy is an essential part of keeping your tree healthy.
But learning how to overwinter bonsai can be tricky. In this article, we’ll explore techniques to keep your tree safe outside over winter.
Know Your Tree
Every tree species has a hardiness level, and it’s important to know how much cold your tree can reasonably sustain. Here in Michigan, which is USDA Zone 6a, Trident Maples don’t survive outdoor in the winter, but Amur Maple, which is a similar species, does very well.
In this example, the Amur Maple can remain outdoors with minimal protection year round. If a Trident Maple is going to survive the harsh Michigan winters, it would need winter protection.
Providing Protection to Overwinter Bonsai
If your tree is hardy enough to remain outdoor in the snow, there are two parts of the trees that you will be protecting:
- The part of the tree below the soil surface (roots)
- The part of the tree above the soil surface
Protecting the Roots
The part of your tree most sensitive to cold are the roots. Overwintering bonsai correctly requires protecting them from the cold during the winter months.
Place Your Tree on the Ground
When the temperatures drop below freezing, move your tree to the ground in a safe space.
Insulate Against the Cold
It is common to use mulch to pack around the pot of your bonsai. This provides a layer of of insulation. Snow will also provide a layer of insulation once it has fallen and covered the pot.
Protecting the Tree
The portion of your tree that’s above the soil line also needs protection, even if it all the leaves have dropped.
Shield Your Tree from the Wind
The frigid winter wind can damage your tree. It’s best to place it somewhere that wind can’t directly blow on it. The east side of a structure, like a house or a shed, can provide protection against direct gusts.
Sunlight is another factor when learning to overwinter bonsai. Depending on the type of tree you have, it may need little to no light during its period of dormancy.
In the winter time, deciduous trees need no light, as they will have shed their leaves, which act as solar panels to enable photosynthesis. Without leaves, they don’t need the sun’s energy.
For this reason, some hobbyists store their deciduous trees in sheds or an unheated garage to protect it from winter winds.
These trees will still need some level of sunlight during the winter months, even though the tree is dormant. This is one reason that your conifers are exclusively outdoor trees.
During the cold months, the rule on watering bonsai still applies: never let the roots dry out completely.
Keeping the roots from drying out can be tricky when overwintering bonsai.
Let’s explore how how to manage moisture levels by looking at where your tree will live during winter.
Bonsai Trees Kept Outdoor
For your conifers and hardy deciduous bonsai, snow can be your best friend in winter. When it’s cold, the snow will cover your bonsai and protect a layer of insulation to the roots. On the days where the temperature rises above 32 degrees fahrenheit, the snow will melt and provide water to the roots.
Use snow to your advantage.
Bonsai Trees Kept in an Unheated Garage or Shed
The trees that you keep in a structure overwinter will need a little more attention. They won’t have melting snow to provide water, so you’ll need to monitor the moisture in the soil a couple times per week to make sure it doesn’t dry out. Then provide water as needed.
For bonsai novice, overwintering bonsai can seem like a scary task. You may have worked caring for your bonsai tree throughout the year, and are now afraid that it might die in the cold weather.
Using the basic overwintering knowledge you’ve gained here, you can now approach the winter months with confidence that you can provide an adequate living environment for your tree while it’s at rest.