How do I Protect my Bonsai from Frost?
During winter, your bonsai tree’s health and care depend on where you live and the type of tree you have.
Normally, the deciduous trees start to enter the dormancy period during the autumn month, when they start shedding leaves to reduce moisture loss. The trees need to do this to prepare for the coming winter, and you must not try and overprotect the trees by placing them indoors.
On the contrary, the tropical and subtropical trees should be kept inside if there’s a drop in temperatures below 15 °C. It’s best if you keep them close to a source of light, ideally a south-facing window. They also need humidity to survive.
Protecting your Bonsai from Frost
In many parts of the world, temperatures drop below -10 °C in winter. Trees that have roots deep underground can cope with this change of weather. But for bonsais, it can become a challenge as they are planted in shallow containers and they need extra care in winter.
The woody/temperate trees except for the tropical and subtropical ones, need to be exposed to the cold outside during autumn to enter dormancy. This means that you have to wait until the first frost before you store them inside for winter.
As compared to the top of the trees, the roots are less hardy. Bonsais have a shallow root system and therefore, they are more susceptible to frost. Even though the top growth of a bonsai is hardier as compared to the roots, they can easily be damaged when the temperature rises during the day and the water in the soil is still frozen. Other factors such as wind also aggravate this problem.
If you notice the soil of your bonsai is frozen, it doesn’t necessarily mean that the roots or the tree are also frozen. Because when roots freeze, the entire tree is damaged. When there’s an extremely low temperature, below -10 °C, the root system faces the threat of freezing.
Not all trees have the same level of frost-hardiness. Species like Azaleas that are normally shallow-rooted are less susceptible as compared to some deep-rooted trees. For example, Trident Maples and Magnolias should be given more protection when the temperatures drop below freezing.
To protect the soil and roots of the tree, you should place the pot in a covered shelter. Unheated places like a shed or garage are best for this purpose, since the indoor temperature is usually a bit higher than the outdoor temperature.
Another way to protect the soil is by putting the tree back into the ground, although this is only slightly more effective.
It’s best to keep a thermometer alongside your bonsai to keep the temperature drop in check. Make sure not to bring the trees out of dormancy by placing them in heated settings or when exposed to temperatures above 10 °C for days.
Protection by a Cold Frame
Keeping your trees in a cold frame during harsh winter is a good idea. The thicker the covering in the frame, the more protection the tree has against temperature fluctuations. It’s difficult for the warmer air to escape thus preventing outside cold temperatures from causing damage.
Before you place your bonsai in winter quarters or cold frames, make sure you clear any debris around the pot and tree. Remove the cobwebs and insects, if any, and clear all algae and moss from the trunk and soil. It’s essential to take this measure as the pests harbored overwinters multiply rapidly due to the inside warmth.
During the dormancy periods of autumn and winters too, your bonsai soil shouldn’t be dry. However, you should water less in comparison to other times of the year. Ideally, you should check the soil is damp but never sodden.
Different trees require varying degrees of light. The photosynthesis rate drops with the drop in temperature, but below freezing, the photosynthesis continues, though too much light can cause damage. During winter, light is needed in small proportions, and too much sunlight should be avoided.
To conclude, you must take extra care of your bonsais, especially if the weather is extremely cold and windy. You should also keep in mind that different species of plants thrive well in different environments. It’s not a one-size-fits-all.