How To Protect Your Bonsai Trees Over Winter

Protecting your trees over winter can be very important for some trees and their survival may actually depend on it.

I will go through some of the main ways you can shelter and protect your bonsai. Some of these options may not be relevant to you and what method you use will actually be based on what the tree needs, rather than what you think you like the most. 

Make Sure You Know Why We Protect Our Bonsai Trees Over Winter

Before you decide that you are going to protect your trees over you should first make sure you understand why we do it and what you need to take into account before doing so.

Some trees will need more protection than others so it important you understand what your tree actually needs before deciding to use one of the below methods.

I would suggest that you read this, so you can understand it in more depth – What Do Bonsai Need Protection From During Winter?

Leave Your Trees Where They Are

Some trees will not need protecting and you can just leave them where they are all year round. This will of course depend on your trees and your climate but you may find after doing some research that a lot of your trees are tougher than you realised.

This is also usually the case if you are growing native trees. They can usually survive in your local climate and will not need much help.

I personally live in a very mild climate as well as having a lot of species that can happily grow here, so I don’t need to give my trees much winter protection, I just leave them in the same spot all year round. You will probably find you have a few trees you can do this with too.

(You can read more about – Are Natives Species The Best Trees For Bonsai?)

Place Your Trees In A Sheltered Location

Simply sheltering the trees from the extremeness of the weather can be more than enough to protect them.

This can be as simple as placing your trees up against a wall to protect them from the direct winds. This doesn’t seem like much, but it can really take the edge of and can really make a difference.

Another very common way to shelter your trees is to just place them under your bench. This is again going to protect them from wind, but more importantly give them a little overhead shelter. This can help keep excess rain or snow off your trees. If you live somewhere every wet this can be very helpful as too much water in your pot over winter can be trouble.

You could also use any sort of overhead structure. A lot of people put their trees up against the house wall where there is an overhang above. This is sort of a mix of the two, you have the wall for protection and the overhang to help keep the majority of the snow and rain off them. 

These trees are still exposed to everything, but this little bit of shelter can do a lot. This is something that we could all easily do, even if our trees can survive just fine in our climate.

I actually have my trees up against the wall all year round and that is all I do. I do think some of my trees could do with some over head shelter and I think in the future I will place my trees under benches; I just need some benches first.

Bury The Trees In Mulch

A very common method is to bury the trees in mulch. You just place them on the ground and pile on the mulch. You don’t need to cover the whole tree, just the pot and the tree can poke out from the mulch.

Doing this helps insulate your roots and the pot as protects it from the direct cold and is a very effective way to do things. 

Keeping trees in bonsai pots does lower their ability to handle the cold, since they are in shallow pot with shallow rots that are basically above ground. By burying them in mulch it is sort like putting them back into the ground, where it is not as exposed to the direct cold and frost.

The best part is that they are actually not buried in the ground, they are still very much in their pot and still have shallow rootballs, all you need to do is remove the mulch in spring and you are exactly where you left off last season.

Unheated Structures Will Protect Your Trees

Any sort of unheated structure can make an amazing shelter for your trees over winter. This can be anything like your shed, garage or unheated basement.

You could also use a greenhouse, polytunnel or cold frame if you have one of these. These are going to keep everything cold, but they should keep the direct frost off your trees. This is ideal for trees that can handle the cold, but maybe not to the level of your environment.

This is also a very good way to overwinter any indoor trees that shouldn’t really be inside. I grow a number of trees inside that really should be outside. They need a cold period, which I cannot give them inside, but I can also not put them directly outside as they will not be used to the lower temperatures and their roots will not have hardened off enough over autumn to actually handle the cold that they normally can.

Placing these types of trees into my shed makes sure they stay cold, without actually running the risk of being exposed to frost.

Most people worry about doing this as these types of places can be quite dark. However, this is fine. Your tree is dormant so it does not need any light, especially if it is deciduous and has no leaves. 

A Makeshift Cold Frame Can Be Good Protection

You can very easily make a makeshift cold frame/polytunnel by using your benches and a sheet of plastic.

Just place your trees under bench then add a sheet of clear plastic over the bench like a table cloth.

All you hen need to is weigh down the sheet and it’s done. Of course the ends may be still be open, but that is fine if you are just sheltering the trees and this will still allow the air to flow through.

If you wanted to completely seal them in, you could also do this very easily with a bit more plastic sheeting.

This option is especially good if you do not have the space for a larger structure like a shed or green house and is also very cheap to do.

Placing Trees Inside Is Not Really An Option

You should not bring your trees into the house, as tempting as it might be. This is not good for the trees as it is going to be too warm for them.

The only trees that should be inside over winter are tropical ones who really can’t handle below 10°C/ 50°F …where being outside would just kill them.

For everything else, they should be outside and sheltered in one of the ways I have discussed already. This will make sure they are still getting the cold spell they need, while not getting too cold that they get damaged.

A Heated Greenhouse Is Not Needed

A heated greenhouse is not ideal for most trees and usually an unheated one will be more than enough, but of course there are always exceptions.

I know people in my area who grow tropical plants (cactus and succulents) and they have no space inside their house for them, so they use a heated greenhouse to keep things alive over winter.

You also may be one of those people who get the extreme -30°C/ 22°F temperatures and the heat from a greenhouse just takes the edge off and makes it like 1°C/ 33°F degree or something crazy.

Basically heated greenhouses will have their place, but really it depends on your circumstance and I think the vast majority of us can survive without this luxury.  

Using Fleecing As Protection

I haven’t really seen fleecing used in bonsai, so I don’t know too much about it. However, this seems to be as simple as wrapping some fleece around the whole trees. This then prevents the frost touching the tree directly, so it is normally used to protect evergreen leaves/needles as they still have their foliage in winter.

This seems to be more popular for trees planted in the ground. I think for us bonsai growers it makes more sense to just move your trees so they do not get touched by the frost, rather than wrapping them up in fleece every time you think frost is coming.

However, the option is there for you if you want to experiment with it.

Using Bubble Wrap As A Winter Protection

Bubble wrap is another technique I don’t know much about and do not really hear bonsai people talk about. This seems to be when you just wrap your pot and soil in bubble wrap. It seems stupid to me, as I feel like it wouldn’t do anything useful.

Doing something like this would help keep the heat in, but there is no heat, the soil would already be cold. Maybe it keeps frost from getting directly at the roots, but I still think the whole thing could freeze and of course the top of the tree is still exposed.

I just think there are better methods, but if you do this and it actually helps, let me know.   

Other Things To Consider When Protecting Your Trees Over Winter

Sheltering your trees is going to be best option for them, but you still need to consider a few risks before you do anything. You will need to make sure your trees still have water and are not effected by mould.

Watering

You will still need to check if you tree needs watered throughout winter. Usually it will not need much, if anything, but you still need to check.

The more sheltered your tree is the more likely it will need to be checked for water. I find the trees that get rained on are usually fine. The rain is enough. 

However, any trees I have kept in the shed do seem to stay damp enough and not need much water over winter, but as its inside a structure it will not get rain and I need to make sure it stays damp.

Just make sure you still check, but do not be surprised if everything stays damp for a very long time and you may need to water very infrequently.

Mould

Mould is also a risk with trees you are protecting over winter, especially inside structures such as green houses and cold frames.

The damp air along with no airflow can make mould develop and I always get this problem with my trees in the shed. Increasing the airflow will solve the problem but this not always easy to achieve.

I just let the mould grow and then remove it at the end of the winter. It usually grows on my trunks and some branches and I just brush it off with vinegar and a toothbrush. 

It’s not really big problem for most trees, but it is something to be aware of and look out for if your trees are not at full health.

Are People Really Protecting Their Trees Over Winter?

You may be thinking everything I have gone through is very over the top and you might be thinking no one does this, so I asked my subscribers if they protect their trees, and here are the results:

As you can see, most people do. 71% of people protect their trees and I would imagine that the 29% who said no, only said no as the type of trees and the location they are in, is totally fine for their trees. They can handle the conditions they are facing. If you are not sure if your trees can do this, check out the link below where I go through how you can work this out.

Conclusion

Now you can see the main ways to protect your tree over winter and as you can see, most of them are really simple and something you can all do.

The important thing is to just make sure you are not bringing trees that need a dormancy period inside as this will really mess them up. You may think you are protecting them but your kindness will actually kill them in the long run.

Protect you trees in one of the ways I have discussed and they will be very healthy and burst back into life again in spring.

(You can read more about – Working Out How To Over Winter Bonsai Trees)