How To Decide If You Should Over Winter Bonsai Seedlings (And Where To Put Them)

Making sure you over winter your bonsai properly is extremely important and it is even more vital to get this right when you trees are still seedlings.

Seedling can be very delicate and they are really not going to survive winter on their own in most situations, so you need to make sure you can protect them. Luckily it is very easy to make sure they are safe, but I will go through everything you need to know below.

You Need To Take A Different Approach With Seedlings Compared to Trees

While your fully grown bonsai and your seedlings may both small be trees, how you approach over wintering them is going to be slightly different.

A lot of the techniques we can use are pretty similar; it is just that we put even more thought and consideration into what we do with the seedlings since they are so delicate and as this will also be their first winter, it is important to make sure they are strong enough, or protected enough to actually survive it.

What Species Is Your Seedling?

Before you decide to do anything with your seedlings, you first need to know what you are actually growing. Different species are going to be able to handle the cold very differently, so it is important to know what you are working with so you can look up their requirements.

If you are growing a tropical tree then you can just keep the tree inside all year round, it will not need a winter, so your problem is solved.

However, if you are growing a species that does require a cold spell, then knowing how to get them through a winter without dying is going to be very important.

For some species, you might not even need to protect them, they may be able to handle the cold and so long as they are old enough, they shouldn’t have any problems.

How Long Has It Been Since It Germinated?

One of the big differences between over wintering a bonsai and a seedling is the fact that seedlings are extremely young, and you need to take into consideration how long the seed as actually been germinated for.

You can start seeds at any time of the year, thanks to cold fridges and warm houses, but when we do this, we are kind of ignoring the natural cycle of the trees …which then mean our new little trees may be out of sync and we need to take that into consideration when we want to over winter them.

Really all this comes down to “has the seedling built up enough strength to survive” and that means we need to know how long it has been since its germinated.

If you look at nature, a seed will germinate in spring and then it has all of spring and the summer to bulk up with energy before autumn comes, when it will then start preparing itself for winter. That’s a good 6 months of growth from when it germinated to when it starts getting cold.

If you have germinated you seeds in autumn …there may only be a few weeks before it gets cold, so of course your seedling is not going to have built up the same strength levels as a seedling that has been growing all season long, so you will need to make sure it is protected. 

How Long Have Your Seedlings Been Outside?

While their age is important, so is the amount of time they have been outside.

A seedling that has been growing happily inside all season is not going to be as tough and ready to handle the cold compared to a seedling that has been outside for most of the year. 

Ideally you want to put your seedlings outside as soon as they can handle it, which will of course depend when you started them. If you place them outside in spring or summer it is going to be fine, they are going to easily acclimatise to your environment and are naturally going to be able to prepare themselves to shut down and get ready for winter.

If you have kept them inside all season then decide to put them out in autumn, they are not really going to be ready to face the cold, they will still be trying to adjust to the different environment when winter hits and it will end badly.

You Need To Tie All This Together To Work Out If They Need Protection

So the 3 points above (the species, how long it has been since they have germinated and how long they have been outside) are all important, but really you need to tie these all together to give you an understanding of how well your tree is going to be able to handle the cold.

The species you are growing may be able to handle the cold, but if it is only 2 weeks old, and never been outside …it isn’t going to be able to handle the cold …where as a tree that can handle the cold and has been growing outside, since early spring, probably can be strong enough to face winter.

Then if you look at a tropical species, it doesn’t matter how old it is, or how long it has been growing outside … it isn’t going to be able to cope with the winter, so it will need protected.

Looking at all three of these together is going to give you a rough idea if your tree is going to need protecting or not. However, if you are in any doubt, just protect your trees.

It is often better to be safe than sorry. As your tree grows you can revaluate if it will need protecting or not over the following years.

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

Where Can Place Your Seedlings To Over Winter Them?

Now that you have decided if your tree needs protection, or not, you need to look at where you should actually put your trees to protect them.

Outside

For some seedlings the species and climate are a perfect match. Leaving them outside will not be a problem.

If your seedlings have been growing all season and they are strong and happy in your climate, then just leaving them to do their thing outside should be fine.

If you look at my trees, such as my Horse chestnut or Sycamore, these both germinated in spring and grew all season long, they are also native here …so they can just be left outside.

Outside, But Sheltered

If you have any doubts about your seedlings strength or you know they are not old enough, or acclimatised to your environment, then protect them.

This is also going to be the case if you just know the species is just not designed to handle your climate

You can protect your trees in a number of different ways, which I cover in this article – How To Over Winter Bonsai

If we look at my trees, I grew a Japanese black pine, it germinated in spring but I kept it inside for the growing season. It was pretty strong and healthy (as it was growing under grow lights) but it had not been acclimatised to outside, so although this species can handle the weather …my tree probably couldn’t, it would have gone into shock from being moved from the warm inside, to the cold outside.

I protected this tree over winter, as it still needed a cold period, and protecting it meant it still got that, but it didn’t get shocked and upset.

Inside

Over wintering trees inside should really only be reserved for tropical trees. They need that warm environment all year round, so putting them outside is only going to kill them.

However, there is a time that you can keep trees inside, that should really be outside.

This will only be when you have recently germinated some seeds and its way to close to winter. In this instance it is better to keep them inside all winter, then introduce them to outside when it is spring time and then go from there.

If we look at my pomegranates, this is exactly what I did. This species can live outside in my climate…but when I grew my seeds it was late October/early November, so basically the start of winter.

There was no way they would have survived outside, and they were also only a few weeks old, so why would I even try and give them a protected winter. That makes no sense. I kind of had to override nature and just keep them inside all winter. They had no idea, they had just been born, and they thought it was spring.

Then when the real spring came, I placed them outside and let them acclimatise. So they kind of got an extra long spring , which isn’t a big deal. It really just meant that when winter came back around they where extra strong as they had a slightly longer growing season and they were then able to prepare themselves for their first real winter.

Conclusion 

Hopefully this makes things a little clearer when it comes to over wintering your bonsai seedlings.

As you can see, you need to take a few different things into consideration and then decide if they need protected or not. So long as you go through this thought process you should end up making the right choices and keeping your trees healthy and strong over winter.

Always remember, if you are in any doubt, protect the seedlings and then re-evaluate the situation again the following year.

(You can read more about – Starting A Bonsai From Seed – A Guide For Years 1 To 5)