Substrate Considerations Part 1

What substrate do you use? I think this is one of the most common questions that keeps coming up on the Bonsai groups. Even if these words aren’t part of the question if often comes down as a factor when considering if you are overwatering or underwatering etc.

I am not sure the question also comes with enough information to provide an answer that helps in their situation. You see, the mixture depends on a variety of conditions such as the pot, plant, your location, placement of plant, growth expectations, etc..

We are also placing this post in the general category as I have found many issues concerning bonsai are also issues when keeping other plants. I keep orchids, adenium, flowers, fruiting plants, vines, and even succulents, so my substrate application is not 100% the same in each instance.

This post will cover general substrate considerations and potential paths forward that might apply well to your situation. We will post more specific topics along the way.

Location

We live in the Philippines and somewhat near sea level. We are about 1km from the Sea of Camotes. There are dry seasons here and rainy ones that bring torrential rainfall for days if not weeks at a time.

Another primary concern for me in making the substrate is that in the rainy season or during typhoons I cannot control the amount of water they get from the clouds, therefore my substrate is biased towards maximum drainage. If we aren’t getting the rain then I water more often.

Growing Stages

Here we have different stages of bonsai and it makes a difference to the substrate compostition. Receiving, growing, and finishing.

Are you receiving a plant and just trying to get it growing again in your environment? Be careful here, as I tried to add more regular soil to the mix and it caused more issues with acclimatizing the plant than it helped. Don’t cause root rot!

Are you growing or training the plant? Well then we place the tree in a large pot and work towards trunk growth and size. In this case we sometimes take the pot and sit it into a planted or the primary soil. In this case the roots will grow into the ground and again, it is for gaining size.

Are you finishing it? Here is when the substrate is critical formy plants. As I said it can rain a lot here so our substrate allows for drainage, drainage, and drainage.

Another Consideration

Availability of substrate materials and their costs will always be a factor for most keepers. When I started mixing substrates I paid far too much for materials than I wanted, and later I found other sources that charge far less for a sack of substrate.

I can’t find a Bonsai mix here unless I order it online and pay shipping of heavy items. Not really cost effective and I have far too many plants to make that even remotely intelligent.

Over time I found a garden center in Cebu City. It is far from us and so delivery can cost a bit. We order about 30 sacks at a time. These sacks are about 20 kilos each.

Substrate Composition

Due to all of the above, we use 4 materials in our mixing now.

First, we use pumice at a size of about 1/3 inch or 1 cm. I like the esthetic of pumice, its weight in a pot, and its durability. White materials here.

Second, we use lava gravel at about 1cm in size as well. Here it is either red or black;here black. I prefer red, but in a pinch black is fine. Neither color makes a difference to the plants.

Third, we use another size of lava that is like a rough sand really. It is red here. NOT FINE SAND. Fine sand or the powder/dust from lava can block water movement in a pot and also inhibit root aeration and growth. At one time I used a washed river sand and that can be a choice, but NOT FINE SAND. We dont have good sources of washed river sand hence the use of lava gravel. The essential part of this product is that it also acts to bind to the substrate with the plant roots and stabilize the plant in the pot.

Lastly, we do sometimes add a VERY SMALL amount of 5 in 1 soil or potting soil. At this stage of our Bonsai I don’t ever add more soil to the mix, but when repotting I think the substrate has somewhat broken down a bit or had some soil in it before, so I will add a small amount of this to my mix and reuse substrate so I dont just waste it. In the picture below you can see some larger stones as well. They were part of a planting at some time before I got the plant. I buy collection or plant materials at times.

When I repot I also remove plastics, broken glass or other foreign materials that I sometimes find. Heck I even found someone’s house key in a pot. I hope they did not need it to get into their house. Lol.

So, living here in the Philippines I have substrate that provides significant drainage.

Enjoy the garden!