Adding moss is one of the best ways to improve the aesthetic of a bonsai tree. Not only that, it is a fantastic tool for maintaining water balance and promoting healthy root growth.
Many people struggle to grow moss in a bonsai pot, but there are some simple tricks you can use to get moss growing on your bonsai. Read on and we'll tell you all about the best ways to grow bonsai moss.
- Why grow moss on bonsai?
- Best moss for bonsai
- Sphagnum moss for bonsai
- How to grow bonsai moss
- Growing moss on indoor bonsai
Why grow moss on bonsai?
Moss is one of the most overlooked parts of bonsai tree care. It enhances the look of your trees by giving the impression of greater age and makes them look more natural. But better than that, moss can massively boost the health and well-being of your bonsai in many ways.
Bonsai moss advantages
There are a few horticultural reasons to be cultivating moss on your bonsai's root ball. It helps to balance water distribution in the pot and reduces water loss, protects the soil from erosion, promotes healthier root growth, and develops a healthy ecosystem of microbiology in your bonsai pot.
Watering becomes easier
Having a good layer of moss growing around your bonsai has a few benefits when we are watering our trees.
First of all, moss draws water upwards through the pot. This counteracts the draw of gravity pulling it downwards and helps to create a more even distribution of water across the whole root mass.
Secondly, moss will slow the evaporation of water from the pot, allowing the tree to make full use of the water and increasing the length of time required between waterings. It is obviously more convenient to water less, but this can also act as a lifeline for trees that may have missed a watering for whatever reason, say if you got stuck at work.
Finally, moss can act as a guide to help you decide when to water your bonsai. If the moss is moist, then you know there is enough moisture in the container. When it becomes dry, it's probably time to water your tree.
Soil is protected
If you are using soil with an organic component, such as akadama, the soil will break down over time when exposed to the force of water from our hoses or rain. This breakdown is called passive decomposition of soil and can result in a compacted layer on the top of your root ball.
This prevents water from flowing through the pot properly and is not a good environment for roots to grow in. A condition such as this is inevitable over time and will need to be fixed with a repot or vacuum clean-out.
Moss helps to slow this process by adding a protective buffer for roots. The main force of the water will be taken up by the moss, instead of the soil particles.
Passive decomposition will still occur as akadama swells and contracts through the absorption of moisture or freezing over winter, but moss helps to slow the process and extend the time your bonsai can stay in its pot.
Healthier root growth
Bonsai moss helps to promote root growth in a couple of ways - by stabilizing the soil surface and providing a dark environment.
Roots can only grow when they are immobile. This is why it's so important to tie your tree down when repotting, but the same concept applies to roots growing near the surface of your bonsai pot.
In a pot that has no moss, soil particles will be disturbed and move each time the tree is watered. They may not move much, but it will be enough to significantly reduce the potential for root growth.
When a bonsai pot has a healthy covering of moss, the soil underneath no longer moves during watering, allowing the tree to populate more of the pot with roots.
Roots also favor dark environments to grow in. Without moss, the topsoil is exposed to the full light of the sun. Moss absorbs most of the light passing through it and creates a darker environment in the pot, promoting root growth.
Moss helps friendly bacteria and fungi to grow
To grow a healthy bonsai, you need a supportive ecosystem inside the container. Many advantageous bacteria and fungi can live in our bonsai pots in harmony with the roots of our trees. They feed nutrients into the roots and benefit from the sugar-rich environment that the roots provide.
Having a top layer of moss on a bonsai pot aids this process. Moss can deposit sugars in the pot, which promotes the growth of these healthy organisms, ultimately strengthening your bonsai.
Best moss for bonsai
The best moss to use for bonsai is one that grows in your local environment. Moss can be quite specific with the growing conditions it thrives in, so if you try to purchase some online and cultivate it yourself you may be disappointed when it doesn't grow well.
By collecting moss that is growing in your garden or near your house you can be sure that you have a variety that will thrive when transplanted to your bonsai.
When applying moss to the surface of a bonsai pot, I use a mix of locally collected green moss and dried sphagnum moss in a 1:1 ratio. I find this to be extremely effective.
Sphagnum moss for bonsai
Sphagnum moss is a fantastic tool in bonsai cultivation that can be used for several purposes. It has many properties that make it ideal for bonsai cultivation, such as a good water holding capacity, large fiber size to allow aeration and unique antimicrobial properties that limit the growth of anaerobic bacteria that may cause root rot.
Sphagnum moss for topdressing
As mentioned above, dried sphagnum moss can be used as a component in top dressing for bonsai pots. Once purchased it should be ground up on a sifting screen and mixed with locally sourced green moss before being applied to the top of the bonsai's root system.
This top dressing will protect the soil, retain moisture and encourage good root growth.
Improving your bonsai's nebari with sphagnum moss
A fairly common problem with the nebari of some trees is the growth of finger-like structural roots that contain no roots between them. This aesthetic can detract from the value of your tree.
You can improve the nebari of your bonsai by packing the base with sphagnum moss. This encourages the growth of feeder roots between the structural roots. These will lignify over time, improving the base of your tree.
Creating rock plantings with sphagnum walls
Sphagnum moss is great for creating rock or slab compositions. Once you have attached a tree to a rock, it will need a path for the roots to grow down into the container.
The best way to do this is with sphagnum moss. I use high-quality dried sphagnum moss that I rehydrate in a bucket of water before application. The moss generally sticks very well to the side of a rock, but can also be held in place with wire if required.
You should place a thin layer of sphagnum on the wall of the rock, pass the tree roots over it then wrap them with some more moss. You may also want to add some soil such as akadama if the roots are a long way from the pot, but this is not essential.
Once you have created your path to the container you can apply locally collected green moss to give the appearance of a long-established tree. Over time the moss wall will erode, but the roots that have grown down through it should lignify and hold it in place.
How to grow bonsai moss
When cultivating moss in a bonsai pot there are a couple of options you can choose.
The first is to apply solid blocks of moss to the pot intact, merging them to give the appearance of an established blanket of moss. This is generally done before exhibitions.
This other method is to dry and grind up your moss, applying it as a top dressing. This method is much better for the health of your trees.
Applying bonsai moss for exhibitions
When applying moss to a bonsai tree for exhibition the difficulty lies in making it look like the moss has been there for years. To do this well you'll need a good supply of moss (roughly 1.5x to 2x what you think you'd need) and a pair of tweezers.
Starting in one corner of the pot and working inwards, place pieces of moss onto the soil mass. You want to place each piece in immediate contact with the pieces next to it, squashing them together so there is no sliver of soil visible between them.
As you apply each piece of moss, compact it down with the flat side of your tweezers.
Fitting these pieces together can be a bit of a jigsaw, and badly positioned moss can stick out a mile. That's why I recommend getting so much more moss than you need on the pot - it gives you options to choose from. If needs be you can also prune moss to fit, but be aware this can sometimes give an unnatural edge to some pieces.
After you've applied the moss water it well, then mist it daily for two weeks to help it establish itself.
Growing moss inside the bonsai pot via top dressing
This method of moss cultivation is less for show and more for the horticultural benefits we listed above. Every tree in my garden gets this same application following a repot.
First of all, we need to prepare the top dressing. I use a mix of dried sphagnum moss and dried green moss in a ratio of 1:1.
The green moss I source from my garden (it grows everywhere here in Scotland) or reuse from the tops of trees that have been repotted.
Grind these two moss types individually over a soil sifting screen to give nice, small pieces of moss. You should wear a mask when doing this so you don't inhale any of the ground-up moss.
Then mix the two mosses before sprinkling a layer over the top of a freshly repotted bonsai. Misting the top dressing with a spray bottle will make it stick in place, and you can then water your bonsai as normal.
Over the proceeding weeks and months, the top dressing grows into a healthy covering of moss.
You don't have to do this after a repot, if you have trees in your collection that you want to cultivate moss on then you can do this at any time of year.
Growing moss on indoor bonsai
Growing moss on a bonsai you're looking after indoors presents a bigger challenge, but having a mossy pot is achievable.
The problem with trying to grow moss indoors is that the air is much drier inside. Air conditioning or central heating will dehumidify the air, which in turn dries out the moss on your bonsai faster.
Moss grows well in humid environments, so to grow it indoors you need to replicate this.
Some people will advocate the use of a tray filled with water under the bonsai pot, but my preferred approach is simply to moisten the moss with a spray bottle once or twice per day.
This does make watering the tree more challenging, because it is harder to know when the soil is dry, but will diligence and experience can be done relatively easily.
It's also important not to spray too much water when misting or you may end up overwatering your bonsai.
I use the same top dressing technique described above to innoculate the pot with moss spores, then let them do their thing.
This Jade bonsai that featured in a previous blog lives on the desk next to my computer and it's moss has been growing nicely since it was potted up 3 months ago.