How To Take Care Of Bonsai Tree In Winter?- Overwintering Bonsai Trees.

How to take care of bonsai tree in winter is one of the most common queries we have received from bonsai owners. So first thing first, I assure you that if you have the same query or your bonsai is facing difficulties in winter, you are not alone. 

Only you know how much effort you have put into your bonsai and you don’t want a gust of chilled wind going over them and ruining all your hard work.

With winter approaching, your bonsai will prepare to combat it like its big tree counterparts in the wild. But as bonsai, they are more vulnerable as they are not rooted in the ground and you are the only one they will depend upon for protection. 

As a part of the bonsai cultivation community, I dealt with hundreds of unique bonsai species and experienced their ups and downs in winter, so I think I’m eligible enough to guide you in this matter. 

Quick facts:

• Bonsai trees can handle less than their ideal temperature for a few weeks.
• No matter how hardy your bonsai is, if the temperature is below 15 degrees Fahrenheit your tree needs some kind of winter protection. 
• Juniper is one of the most winter hardy bonsai.
• Bonsais that love bright warm conditions (e.g. oak, maple, juniper) benefit from outdoor winterization. 
• The majority of the bonsais do fine with minimal winter care. 

Now let’s talk about how to take care of bonsai tree in winter care in detail; 

Things to consider while taking care of bonsai tree in winter:

There are a few key points you need to keep in mind before providing winter protection to your bonsai. These will help you to decide on the level of care each bonsai needs. 

The region you are living in:

Coldness in winter hits differently in different regions. That being said if the winters are mild where you live (temperature hardly drops below 30 degrees F) your tree wouldn’t require any kind of protection. 

Species of bonsai:

Ignoring bonsai species is the most vital mistake bonsai parents make while taking care of bonsai tree in winter.

We often believe all bonsai trees need winterization during winter or can’t be left outdoors during cold temperatures. 

This is simply not accurate. 

Temperate species like maple, juniper, and elm, the majority of coniferous and deciduous species can tolerate inconsistent levels of cold temperatures in winter. In fact, many of them demand certain low temperatures for a specific period of time, or else they will lose vigor or fail to produce fruits and flowers. 

This isn’t the same for sub-tropical or tropical bonsai species. Trees like ficus and jade don’t expand well when it gets cold. Tropical species that are cultivated indoors typically don’t demand special bonsai winter care, but outdoor bonsai, need winterization if the temperature goes below 40 degrees F. 

Indoor and outdoor bonsai:

Care of bonsai tree in winter typically looks very different depending on the placement of the bonsai.

Indoor bonsai trees like maple, ficus retusa, and Fukien tea should stay indoors in winter as well, as they need warm temperatures to survive unless the temperature of your area stays over 25 degrees Celsius all year round. 

Outdoor bonsai require protection depending on the levels of temperature fall it faces during winter months. If the lowest temperature (zero degrees Celsius) stays only for a few days, it can live without any protection, but if it stays for a longer period of time it requires to be kept inside a shelter or under shade. 

Determining which species of your bonsai tree needs protection in winter:

To determine which bonsai needs winter protection, understanding their hardiness zone is important. The accurate way to determine bonsai’s cold hardiness is to compare the plant’s USDA  hardiness zone and the zone you are growing the tree.

But the issue is that the zone designation is limited to in-ground plants and as bonsai live in containers temperature falls affect them much harder than inground plants. 

There’s a book called  “Bonsai Heresy” by Michael Hagedorn, which is like a cheat sheet for bonsai owners. It has a detailed description of the cold-tolerant power of different bonsai species. 

[To learn more about the book check out Bonsai Tonight’s review.] 

• ​Individual toughness also plays a vital role in the cold hardiness of two trees of similar type. It happens when they grow up in two different atmospheres. 

• Just like older people need more warmth in cold weather compared to young, active folks, your older bonsai needs extra protection than the younger ones, especially if you see them losing branches in winter. 

• If you just recently plucked a tree from the wild or dug one up from the ground, these trees need extra care in the winter, because they are not used to the cold yet.

• The size of the pots your bonsai trees live in matters too. Bigger pots provide better insulation for the roots, like a big, cozy jacket. Smaller pots are like thinner jackets, so the roots can get colder.

• And if your bonsai tree was sick before, like if it had bugs or a fungus problem, it needs extra attention while you are taking care of bonsai tree in winter.

Hardiness detection can be done by your observation, but here’s a list of trees according to my observation;

How to prepare your bonsai tree in winter:

Before winter preparation: 

During the warm and dry months (May to mid-November), let your bonsai bask in the sun outside to develop well. Refrain from fertilizing it by August to prepare it for its winter rest, and avoid heavy pruning too close to winter to ensure it goes into the cold season strong and healthy. It’s all about timing and giving your bonsai the best circumstance to flourish throughout the year.

During winter preparation:

During the dormancy time, consider moving outdoor bonsai trees to a cool, unheated area for shelter. If your bonsai belongs to a hardy species, leaving it outside is an option, but you have to ensure it has enough protection against harsh winter situations.

When cultivating bonsai indoors during winter, artificial grow lights aren’t crucial if the storage temperature remains between -6 to +10 degrees Celsius. This temperature capacity allows many bonsai trees to go through dormancy without vigorous expansion.

Being familiar with your local climate is important for determining the level of protection your bonsai trees will need during winter. Different regions have varying challenges, such as heavy snow or extreme cold.

For helpful insights and guidance particularly in your area, reach out to local bonsai enthusiasts or clubs. They have knowledge of overwintering bonsai in your region and can offer guidance on winter care and shelter options for your bonsai collection as well.

However, here are some of the important steps you can take in order to prepare your tree for winter;

• Firstly, to keep things clean and tidy, start by taking the brown leaves and needles out of deciduous and conifer trees. Ensure there are no signs of fungus or insects, if detected treat them immediately. As a precautionary measure, you can use dormant oil in winter. 

• Next, deal with the fertilizer built up on the soil surface. They form a crust on the top of the soil, which makes it hard to consume water. So you should remove the crusty top layer and replace it with a fresh layer of soil. 

• Lastly, give your bonsai a taste of cold weather, it’s an important and natural reminder that winter is coming and it’s time to rest. 

Now that your tree is prepared it’s time for winter storage. I will be sharing the strategies I have followed for years.

Placement:

If the temperature drops below 20s (F) for days (happens in my area), put them under a bench, so that heavy snow load and wind will not catch it.

Learn about the ideal placement for your bonsai in detail.

Bury Them In The Ground:

Even though I personally haven’t tried this method one of my bonsai enthusiast friends swear by it. He advised to dig holes that are large enough for your bonsai pots and fill them with soil until it’s just past the pot’s rim. This will help insulate the roots.

If it snows, you can shovel snow around your bonsai trees, all the way up to the first branches. This extra layer of snow will provide even more insulation and keep your trees cozy during the winter.

Mulch beds:

This is what I usually do to imitate the burying-in-the-ground situation. I create a mulch bed with straw, bark, and leaves and spread it up to the first branch. For a little more protection place them near a wall and cover them up with a plastic.

Unheated Garage And Sheds:

You can place them on tables, shelves, or even directly on the floor. Another idea is to create insulated spaces within your garage to keep them safe from the cold.

Cold Frames:

Standard cold frame

DIY plastic wrap

Cold frames are greenhouses but stay cold. You can create it with various materials like wood and plastic sheets. For detailed guidance, you can check out Home Depot’s article about it. 

Some Additional Tips:

• Avoid cold winds as it is the most dangerous element for bonsai in winter. They dry out the tree resulting in losing branches. 

• Your bonsai will require moisture even when they are not active. Once a month but it’s unavoidable. So make sure to water it well.

• Try to keep the temperature between 33 and 40 degrees F, it will help them to go dormant without exposing them to harsh temperatures.

• ​Keep the temperature mentioned above as long as possible, as sudden fluctuations of freeze and thaw will harm the tree even further. 

After Winter:

As trees wake up from winter, move them into the sunlight to keep them strong. But if it gets too cold at night or there’s a storm, bring them indoors to protect them. This daily shuffle can be a lot of work, so some people try to keep their trees dormant longer.

Another idea is to use a warmer greenhouse to encourage early growth, giving more time for spring care.

Common Winter Damages On Bonsai And How To Fix Them:

Winter Dehydration:

It’s essential to understand that it’s usually not the cold itself that damages bonsai, but rather dehydration. When the soil near the roots freezes, the roots are unable to take in water, but the top of the tree keeps losing water. This is why long periods of freezing temperatures can be challenging on bonsai.

If it’s gusty or the air is dry in winter, it can make things even worse by drying out the trees. Keep your bonsai in a sheltered spot away from strong winds and direct sun. This helps protect them from dehydration during the cold months. 

Pest And Disease Control:

In winter, observe for pests like spider mites, scale insects, and mealybugs that can damage your bonsai. Also, be cautious with infections from overwatering, like root rot or fungus.

Check your bonsai often for any issues. If you see pests, use organic insecticides like neem oil. For diseases, water less so the soil can dry out between waterings. This will maintain your bonsai’s health during the cold season.

Dying Branches And Brown Leaves:

Bonsai leaves can turn brown or you might notice dying branches during winter, which is often caused by inappropriate lighting, temperature fluctuations, or poor humidity levels. To control this issue, ensure that your bonsai tree is positioned in an area with good light and temperature control.

You might need to reduce watering frequency and increase humidity levels near the plant using a humidity tray.

Summary Of Tips:

• Bonsai trees can handle some cold, but if they drop below 15 degrees Fahrenheit, they need winter protection.

• Some hardy bonsai, like juniper, can stay outdoors in winter, while others that prefer warm conditions need protection.

• Consider your local climate and the specific species of your bonsai while taking care of bonsai tree in winter.

• To prepare your bonsai for winter, remove brown leaves and deal with fertilizer build-up on the soil.

• Place your bonsai in a sheltered spot, mulch beds, or unheated garages, or use cold frames to protect them.

• Protect your bonsai from cold winds and maintain a temperature between 33 and 40 degrees Fahrenheit.

• In winter, watch for pests and diseases, and ensure proper lighting and humidity levels to avoid brown leaves and dying branches.

FAQs:

Should I feed my bonsai in winter?

It’s better to avoid feeding bonsai in winter, as this time they are least active, and little overfeeding will be enough to give fertilizer burn. Most bonsai don’t require fertilizer in winter but indoor bonsai can tolerate all year-round fertilizing.

Which bonsai is best for beginners?

Juniper is one of the hardiest plants that can withstand temperature fluctuations, less water, and less sunlight. They are easy to prune and shape, making them one of the best beginner-friendly bonsai. 

What is the best location for bonsai in winter?

Bonsai should be kept in a cool yet bright location. Indoor bonsai does best if kept near a well-lit windowsill.