Preparing Your Bonsai Trees For Winter

The inevitable onset of winter, complete with freezing temperatures and prolonged periods of wet weather can without proper preparation cause a range of care issues for the bonsai enthusiast.

Trees from temperate parts of the world such as ours have developed to cope with the cold weather by entering a period of dormancy. Photosynthesis ceases in deciduous trees and slows to a trickle in evergreen species. Tropical and sub-tropical trees can be more tender to the cold. 

Proper fertilisation help to protect bonsai trees in winter

Proper preparation for winter starts during the autumn. Trees produce sugars and carbohydrates which they use to stop themselves from freezing.  It is important therefore to make sure that your trees are well fed throughout the growing season in order to give them everything they need to be ready for the cold.

Cold winter weather can dehydrate bonsai trees

Bonsai trees are generally very hardy and able to cope with cold conditions. Generally it isn’t the cold which harms the tree. More damage is often done through dehydration. If the soil around the roots of a bonsai freeze, the roots cease to function. They stop drawing in water. The top of the tree however continues to release water. It is for this reason that prolonged spells of freezing weather cause harm. This is can be made worse by freezing weather coupled with strong winds  or strong winter sun as it dries the trees out even faster. A lot of the potential harm can therefore be removed simply by placing the trees into a more sheltered position out of the wind or sun.

Don’t rush hardy bonsai trees into winter protection

It is quite common for beginners in bonsai to want to over protect trees by bringing then into the house or into a heated conservatory. This may result in the trees not actually entering the dormancy period – It can encourage them to keep growing. If this happens the trees may carry out growing throughout the winter. This distortion of the natural cycle does not help and can harm the tree. The dormancy period is essential to the health of trees from a temperate climate. Trees from tropical parts of the world do not need this dormancy period as they do not experience it in their natural environments. They can therefore be allowed more heat.

When does the cold kill bonsai trees?

Generally speaking most trees from temperate parts of the world can be left unprotected until the weather gets down to -10. When it gets colder than this, protection is required. Exceptions to this include Trident Maples, Azaleas and Loropetalums.

Tropical trees, such as Ficus, will be damaged by even light frosts and should be moved before the temperatures really start dropping,

It’s important to research the kinds of trees hat you have to find out the degree of cold that they can withstand. 

Size Matters

larger bonsai trees are more robust generally and this certainly applies to the cold. Smaller bonsai trees, perhaps small enough to pick up in one hand, will need protecting earlier than large, heavy trees.

Winter quarters for your bonsai trees

A greenhouse is probably the best solution for protecting trees from the worst of the weather.

An unheated outbuilding can be used to protect deciduous trees. Since deciduous trees don’t need  light when not in leaf, they can be stored in shed, outhouses or garages when the weather gets cold.

Bonsai growers often construct benches in order to display their trees to best effect in the garden. Dropping the trees under the benches and then covering the bench top and sides with bubble wrap or something similar can be enough protection.

Another solution is to take the trees out of their bonsai pots and plant them out into the garden. This can provide the protection from the cold that the roots of the trees require. When the spring comes they can simply be potted back into the same pots.

As with planting bonsai out in the garden over winter, you can take the trees out of their pots and plant them into larger wooden boxes filled with garden soil.

The experience of real-world bonsai growers

As part of running the business, I often come into contact with very experienced bonsai growers. Some of them move all their trees into greenhouses, while others don’t move them at all.

For me, peace of mind also comes into play. Its far easier to relax on a winters night knowing that your bonsai collection has been prepared for winter. Its saves worry on your part. 

Having your bonsai trees protected also helps them get off to a strong start in the spring.