How To Grow Bonsai With Grow Lights

Using a grow light may seem like it is pretty easy, just turn it on and it’s good to go …and while that is true, there are few nuisances you need to take in to consideration when using them to grow bonsai.

The first thing you need to do is ask yourself is – Do You Need A Grow Light? For most of us, the sun should be more than enough to grow our bonsai, but there can be a few occasions where a grow light may be better and if that is the case then you will want to make sure you are using it properly.

Most trees should be grown outside, but there are a few that may be better inside. (You can read more about what are – The Best Trees You Can Use For Indoor Bonsai.)

If you do not use your grow light properly, you can actually harm your trees or even kill them, so you need to make sure you are doing things right. You will now have full control of your trees light levels, which can be a big responsibility.

What Type Of Light Do You Need?

I think it’s important to say that you need an actual, proper grow light. If you are planning to just point your ikea lamp at your trees then you are going to have a pretty big problem.

You need to make sure that the light you are using is actually designed to grow plants; so long as it does this everything will be fine.

If you cannot provide a proper lighting system then your tree needs to go outside and get real sunlight as this will be their only chance of survival.

What Distance Should Your Trees Should be Form the Light?

This will depend on your light and you should read the instructions for a bit of guidance.

There are two things you need to consider. The height and the…I guess you would describe it as how directly over head the light is or its “footprint”.

The Height From Your Trees

Really you want your trees to be about 30 cm away from the light. You can go a bit closer, but I would not go any closer than about 15cm. You can also go a bit higher, and I’d probably say to about 60cm max is probably going to be about right.

The Footprint Of The Light

When you look at your lights instructions it will probably give you a footprint that the light will cover, or a grow area that it can cover. This will of course be affected by how high or low you have the light, which is why you should see what they suggest.

Basically you do not really want to stray too far outside of this footprint or it is not going to get enough light to grow. If you imagine your light as a shower head pouring water down on the tree, the light …or water in this example only drops straight down, directly under the light. If you stand outside this area, or this “footprint” then you don’t get wet. 

The same is true for light, while it may look like the tree is still getting light, it will not be as optimal as when it is actually under the lights direct footprint so you may find a tree growing too far outside of this area does not grow well.

A lot of lights will have this growing footprint mapped out in their instructions and you will notice that the more central your tree is under the light, the stronger and better quality light it will get.

How Long Should The Grow Light Be On?

The amount of time that you keep the light on will really depend on your goals and what you are trying to grow.

However, no matter what you are doing you need to always remember that plants needs darkness!!

NEVER keep the light on for 24 hours. This will actually kill your trees. It’s kind of like if I made you stay awake for days on end, you will eventually collapse and die from exhaustion. Trees need rest too, so make sure you always give them a day and a night.

Keep The Light Levels Natural

You are probably going to be better off trying to copy nature. I pretty much have the light come on at sunrise and turn it off during sunset. You do not need to be super precise, but if you use this a rough guide it makes everything easy.

I know some of you will wonder why not have it on for longer than this, which you could, but really your normal day light hours will be enough. The light will be shining down a full days worth of perfect light and your trees are going to be more than happy and also allows for plenty of darkness too.

You can also then easily adjust the light throughout the year so your trees still get some natural change in levels throughout the year. This is going to make them think they are actually growing naturally outside.

Buy A Timer Switch For Your Light

Do not use your light until you have a timer switch.

If you think you can just turn it on and off yourself you are wrong. This little chore will kill you, but more importantly, if you forget then you will mess up the rhythm of light and dark.

I’m sure doing it once or twice will not really affect the trees, but still, just get a timer and make everything easy and automated.

How I Set Up My Grow Lights

I will explain what I do with my lights and that will give you some real life examples of how I use grow light with my bonsai.

If you don’t know, I have two grow lights. One I actually need as it’s for tropicals and succulents and the other I don’t really need. It’s used more for Mediterranean style trees that can actually survive outside where I am.

I just like to use the light to give them a more Mediterranean type environment so they grow a little better than they would outside here.  

My Tropical Trees

I have this light inside a grow tent that is from the same company who made the light, so the footprint is perfect and I do not need to worry about that as its all designed to work together. (I’m using the Mars Hydro Grow Light) 

 I have the height set to about  40 cm above the tallest tree, but i actually have a number of shorter trees, that are about 55cm away from it.

I could get a little shelf, or stand or whatever to raise some of these smaller trees up a little higher so they are closer to the light, but I have not done this. 

In the height of summer I have the light come on at about 6am and it goes off about 9pm. Outside the sun actually rises earlier and sets later than this, but I feel 15 hours of intense direct light is going to be more than enough for any tree, including a tropical.

I also feel this amount is probably a little closer to the amount of day light you might get if you went further south. I am at around 55° North, so we get long days in the summer.

I leave the light at this setting for June, July and August. I use the following 3 months to slowly lower the light levels. Every few days I change the timer switch and gradually reduce the light down to about 7 hours.

I then keep it at the 7 hours over December, January and February.

I think last winter it came on about 9am and went off at 4pm. This is quite a big drop in light levels over the years, but it is also still quite a lot of light even during the “winter”. The trees do slow down a lot over winter, but they do still grow.

I could probably even it out and do 12 hours a day all year round, it would certainly be easier to do, but I like trying to give the trees a high and low season. It also means I get a bit of rest in winter as they slow down.

My Temperate Trees

This grow light is in a weird set up I made in the corner of my room.  (I’m using the Plant Photonics Grow Light)

The light has a footprint of about 40x40cm. The shape of my grow area is actually 40X60cm, so there is an area that does not have the best coverage. I try and rotate the trees around so that it’s not always the same tree that is in the bad zone and that seems to solve the problem.

The light is also quite low, but that is just because I can’t get it any higher up. It’s at about 20cm away from the tallest tree so it’s still acceptable.

I treat this area like the other one and I constantly adjust the timer every few days to slowly lower and raise the light levels throughout the year.

At the height of summer I probably have it on around the same time as my other light, from 6am to 9pm, which is about 15 hours.

However, the only difference is that I only really keep it at this level for a few days. I then slowly lower the levels down so that by the end of November it’s on for about 2 hours a day.

This is a huge shift in light levels, but the fact that it’s done over a couple of months makes it fine.

I actually get the trees to start shutting down for winter by doing this, which shows the trees are pretty happy and think they are growing naturally.

I then put them out in my shed to actually get some colder temperatures and dormancy in December and leave them there in pretty low, natural light until February.

I then bring them back inside and start them off with 2 hour a day and I slowly just start increasing the levels every few days until I’m back to the summer highs.

This all very labour intensive, but my trees think they are growing naturally and are extremely healthy, so for me, it is very worth it. It takes only a few seconds to adjust the timer every few days.

Other Factors To Consider When Using Grow Lights

While the biggest factor you need to deal with is how to set up the light and how long to have it on for, the other factors of growing a tree are still important, but luckily they are pretty straight forward and very similar to growing trees outside.

Water

You will need to treat this the same as your outdoor trees, but remember the water will come 100% from you. There is no rain to help you out.

You need to be checking every day and you need to realise the light and temperature may affect things slightly differently to a tree growing outside, which is why you should be checking daily to see what is needed.

Pruning

You will probably find that your tree grows a lot better under the grow light, since it is getting a constant supply of perfect light.

This does mean you may be pruning more often. If you are trying to develop ramification you may find you are constantly pruning.

Even though I try and keep my trees in a natural light pattern, they grow so fast that I am often pruning monthly.

Pests

I have found pests usually occur slightly less often. I guess they can’t find the trees as easily inside, but when they do come, its carnage and they will spread very easily and quickly.

So you still need to be checking often, just like you would when they are outside.

Feeding

You should keep your fertiliser regime the same as your outside trees. Just because they are growing more aggressively under the grow light does not mean you need to change anything.

Sometimes too much fertiliser can be a bad thing, so don’t go crazy.

Conclusion

Basically growing under a grow light is the same as growing outside, apart from the fact that you can control the level light, and of course the quality of the light is better much better.

If you set everything up right and take the time to give the trees what they want throughout the year you will find that using a grow light is very easy and you will get very good results.

I do still think for most situations the outside sun is going to be your best option, but sometimes a grow light makes sense, especially if you use it properly. 

(You can read more about – How Much Light Does A Bonsai Need?)