When Do You Fertilise A Bonsai?

I often get asked about when I fertilse my trees and a lot of people think there seems to be some big mystery behind it all.

There really isn’t anything difficult about it and you certainly don’t need to make it complicated …just buy some fertiliser and follow the packet instructions. It’s as easy as that, but I will go through somethings that I often get asked and hopefully clear up any confusion.

What Is Fertiliser?

I think it’s important to start with what fertiliser is and what it does. Everyone thinks it is some sort of magic potion that makes your tree grow, or they see it as “food”.

The reality is that all your tree needs to grow is sunlight and water. If you can get this right, you tree will grow.

But of course fertiliser has it uses and it does help, but it is more like a multivitamin. It gives the tree some extra nutrients that help make things run a little smoother and more efficiently so you can’t really go without it.

Fertiliser is made up of Nitrogen, Potassium and Phosphorus, which can be found naturally in soil and is why plants growing in the wild are very healthy. However, since we use quite a lot of inorganic soil, and we use small pots, it is best if we give the tree some fertiliser to make sure it actually has these 3 compounds available in the soil, so the tree can function at its best.

Why Over-Fertilising Is Bad For Your Bonsai?

There is a real misconception that more is better when it comes to fertiliser, but this is very wrong.

As I explained above, it’s more like a extra nutrients that the tree uses, it helps the process of growth, and it doesn’t fuel growth directly.

This means that filling a pot up with fertiliser doesn’t really help anything. The tree will only use what it can use and more importantly, when you realise what fertiliser is, you can see why too much is bad.

You may have heard fertiliser referred to as salt, as basically the nitrogen, is often made from ammonium sulphate which is a form of salt, so if you pump a tree full of fertiliser, you are adding a lot of salt.

This can really unbalance the soil and make it too salty which causes a further imbalance in the tree. Basically the water levels in the soil and tree should be about equal but when one is more salty than the other you will get osmosis happening to try and balance things out …which means water is actually going to be leaving the tree roots to back into the soil to balance things.

I don’t think I need to explain why water leaving your tree is not exactly ideal, but this can be the result of too much fertiliser and is exactly why you need to be careful with how much you use.   

How Much Fertiliser Should You Use?

If you follow the instructions on the packet you can’t really go wrong. Usually they will have a section for house plants and you can basically follow that advice.

They have tested the product and know how much should be used, so why would try anything else?

More importantly, when you use it in the way they suggest, you will know exactly how much fertiliser your tree is getting rather than just guessing what dose you are using.

How Often Should You Fertilise Your Bonsai?

As for how often, I would again follow the instructions and you should be fine. Personally my fertiliser says to use every 2 weeks during the summer,

However, I go for about once a month throughout the growing season. This just suits my schedule and more importantly makes sure I don’t end up adding too much.

We use small pots, so it can be easy to over fertiliser, but at the same time we use loose soil, so you could easily argue that it flushes out quickly. Either way my trees grow really well when I do this, so I will just stick with what I’m doing.

When Should You Fertilise A Bonsai?

Really should you be fertilising throughout the growing season which means when the tree is actively growing.

You can also keep fertilising into autumn. A lot of people think this is going to make your tree grow when it is trying to shut down, but this is not the case. Fertiliser does not make a tree grow, it’s the temperature and light levels that make it grow… or at this time of year, shut down.  

The whole point of fertilising in autumn is that it loads the tree up with nutrients while it shuts down. This doesn’t really do anything for it at the time, but I have found that it will really make it explode with growth the following spring, which is what I usually want, especially since a lot of my trees are still in development.  

Should You Fertilise In Winter?

Fertilising in winter is a total waste of time. Your tree is dormant and is not really taking in any water, so everything you add is either just going to sit in the pot and end up upsetting the salt levels in the soil, as I discussed before, or it is going to be washed out of the pot. Either way it is not doing anything for you tree, so do not waste your fertiliser.

Fertilising After A Repot?

If you have just repotted your tree, do not fertilise it.

You will have cut the roots and they will be weak and need time to heal. The last thing they need is fertiliser. Adding it is only going to damage them and cause them to get root burn, which is not want you want on a tree with already weakened roots. 

You need to wait at least a month, but really I would say about 6 weeks before you fertiliser. I would also start out quite light and then increase it after this.

Just be cautious and you will be fine.

Is Liquid or Solid fertiliser Better?

Honestly it doesn’t matter. I have used both liquid and solid fertiliser and they are both fine. It really comes down to what to prefer and what you find easier to use.

It is more important to know what is in your fertiliser, rather than worry about how it is administered.

You will find as many arguments for as against each type, so really it is down to you test them out and see which you prefer and which ones you think give the best results. I honestly don’t think it matters as both worth extremely well. 

What Fertiliser Is Best For Bonsai?

This is a question I have answered in this other article – Do You Need To Use “Bonsai” Fertiliser?

Where I go through some commonly used fertiliser in Bonsai,but basically it doesn’t matter. Well it matters, but it’s more important to know what you want from your fertiliser and to understand the different amounts of nitrogen, potassium and phosphorus that each of them contain …Then all you have to do is use the one that will do what you want.

As for specific brands, they are all about equal and really it will depend what is available in your area so it’s not really worth getting too worried about that.

Conclusion

Hopefully this clears up some of the confusion around fertiliser. Just buy some that will suit your needs and follow the instructions on the pack. If you do that, you should be fine.

Just always remember that too much fertiliser is bad, so don’t get carried away and you should find that your trees grow very healthy.

You can read more about – Can You Give “Flower Food” To Bonsai Trees?