Do Humidity Trays Actually Do Anything For Your Bonsai?

You’ve probably seen people use humidity trays in all different areas of gardening and you have probably wondered if they actually do anything useful for your bonsai.

Well, they sort work, but the reality is that they do not really raise the humidity that much and for most people it isn’t really going to do anything for your trees and you are mostly going to be wasting your time.  

What Are Humidity Trays Supposed To Do?

Humidity trays are slightly deeper than drip trays. You fill them up with stones then place your tree on top. You then fill the tray with water, so that it comes up to about the level of the stones. 

The theory is that the water in the tray will evaporate and go up and around the tree, giving the area around the tree some extra humidity.

Why Do Plants Need Humidity?

I think it is important to understand why we might need some extra humidity around our trees, and basically it is related to photosynthesis.

When leaves are photosynthesising, they have to open their stomata, which is basically little holes in the leaves that let the carbon dioxide in …but it also lets water out at the same time, basically the tree swaps the water for the carbon dioxide.

This whole process of the water escaping is called transpiration, it also helps keep the tree cool and it is also the reason why water is being constantly sucked up from the roots, as it has to replace the water that is lost form the leaves.

Obviously the more water the tree looses, the more it has to pump up to the leaves. This is an issue for a bonsai, as we grow out trees in a small pot, so lots of water leaving the tree can put a lot of demand on the small root system and the pot can quickly dry out. 

Humidity plays a big role in how quickly this will all happen. If the air is very dry, the water is going come out of the leaves a lot faster compared to when it is very humid.  (The thickness of the leaves also plays a role in this; thinner leaves will lose water faster than thick ones)

Humidity is just a measurement of how much water is in the air, so if you have 100% humidity, basically nothing is going to evaporate out of the leaves, as the surrounding air is already full of water. This may sound great, but it is also not ideal, as then this slows down the rate of photosynthesis as now less carbon dioxide is being taken in by the leaves.   

This really means the plant needs some humidity to function well. Too little is bad as the tree dries out very quickly, and too much is also bad as the tree can’t photosynthesise and grow efficiently. 

What Humidity Is Best For Your Tree?

The optimum level of humidity is going to change depending on the species, but on average, most trees are going to be pretty happy in and around 50-60% humidity.

You will find some tropical trees can handle a little more, and likewise, desert plants can be comfortable with a little less.

Humidity Is Always Changing

It is also important to remember that humidity can always be changing. Since it is the moisture content of the air, many things can affect this.

The temperature, wind, rain, time of day and even the time of year can all affect the humidity of the room your trees are in.  

What Have Tests Shown?

The effectiveness of humidity trays is something I would like to test myself, but for now we will have to look at the work of others. You can find dozens of tests on youtube, from various plant owners.

Every experiment is slightly different and maybe not fully accurate, but from the wide range of them we can start to see what is going on.     

It looks like that humidity trays only raise the humidity by around 1-4%

This really isn’t all that much and again there are many factors that can influence things. You have the natural factors I mentioned above, such as temperature and the wind, which will all effect how quickly the water evaporated, but you also have many factors around the humidity trays themselves.

The size of tray, how much water was in it and what stones where used in the tray all seem to have an effect too. Basically you need very large trays and a lot of water in them to actually see any decent changes in humidity, which is not really what most people do.

The plants themselves also seem to change things slightly too, changing the results compared to a fully open humidity tray, basically the plant pot reduces how much of the trays surface was open to evaporation, so it slowed things down and didn’t increase the humidity levels as much.  

However, the general consensus is that humidity trays work, but not enough to affect your plants. Really unless you are in a very dry environment, it isn’t going to make enough of a difference, and if you where in this situation, you would want to use other methods to create more humidity. 

Did I Find They Actually Helped With Humidity?

As I said, I haven’t done a test, but I have used humidity trays and also stopped using them, and really I didn’t notice any difference.

I had a tray that I filled with stones to make it look nicer. I then spent some time filling it with water, but I didn’t see any difference with my trees health.

However, I was living in quite a humid house anyway (I actually was using a dehumidifier a lot of the time), so maybe it didn’t matter for me. Also when you consider the fact that a tray may only increase the humidity by 1% it makes sense that I didn’t notice any changes. 

There may be a few of you reading this who live in a very dry environment, and you might actually notice it helps. If you think it helps, keep doing it. 

Should You Use A Humidity Tray?

For the majority of us, we probably don’t need one. The humidity we have is probably fine and changing it by 1% isn’t really going to make much of a difference. 

However, if you want to use one I would ask yourself some questions. Don’t just blindly use them. Find out how humid your room is and also how humid your tree need to be.

If you think you are in need of more humidity then test it and see if you notice any difference. You probably won’t, and if you do notice any changes, it will be other things affecting it, such as you are now giving the tree more attention and learning to care for it properly, rather than it being a small increase in humidity.

(You can read more about – Do You Need A Humidity Tray For Your Bonsai?)

If You Want Real Humidity, Use A Green house

If you really want your trees in a humid environment you need some sort of green house. This is going to trap a lot of the moisture in the air and will make that area be significantly more humid.

I actually find my grow tent has the same effect. I often open the door to get met with a wave of warm, wet air. I did have a humidity meter in there, but it broke. I can’t remember what the readings where, but I know it was higher than the rest of the room.  

Other Things You Can Use To Get Humidity

If you don’t have a green house or grow tent you can use some sort of dome to make a mini green house.

I have a seed tray designed for germination and it has the seed tray and then a clear plastic lid. This is basically a mini greenhouse. Although it is not very tall, so it is not great for bonsai as they can’t fit in.  

If you really want humidity, then you need to get a humidifier, this will just put out water into the air and raise the humidity of the whole room. This is going to do a far better job than a humidity tray and if you live in a dry climate, this is what will actually make a difference for your trees.

They Can Be Good For The Roots

While I don’t think trays do anything for the humidity, they can still be useful and they can still help your tree.

They are of course a drip tray, so they will catch the mess, but they are also a reservoir of water and you will find a lot of trees will poke some roots out of the bottom of the pot to get access to this water.

This is especially true for mame bonsai that are growing in tiny pots. These small pots can dry out pretty quickly and sometimes they don’t even have enough space to even cater for the trees basics needs, so this extra water below them can really make a difference and actually help keep them alive.

This isn’t really anything to do with humidity is more to do with just having access to more water.      

Conclusion

Hopefully now you can understand what humidity trays are suppose to do, and how they don’t really do it.

They are supposed to raise the humidity, but the reality is that they only do this by a very small amount making them pointless.

If you really need more humidity, then using a greenhouse or humidifier is going to get you much better results than a tray of water.