How to Make Pre-Bonsai Soil

3 months ago Nebby 0

Source: Practical Bonsai Blog.

Regardless of if you’re potting seedlings, rooting a cutting, or just giving something small time to thicken up, there are lots of reasons you might be using pre-bonsai soil.

I basically categorize material to plant in two basic categories. Things I’d stick in a bonsai pot, and things I wouldn’t.  When you pot something into a bonsai pot you are stopping most of the growth, much the way that when you start cutting back long thick branches while you’re structural pruning you’re beginning to train the tree to produce smaller growth.  In my other article What Kinds of Bonsai Soil Should I Use I talk about what components are in bonsai soil and what to pot your bonsai in. Several other websites talk about this too. What I don’t see many people talk about is what to pot your PRE-bonsai in.

Most all agree that potting soil is just terrible. (Boo! Potting soil stinks!) The reason it stinks is because it’s generally too wet. By which I mean it holds on to moisture longer than we’d like.

Over time I’ve come to a new modified recipe for potting soil. I pot pre-bonsai and regular herbs and potted plants in it.

Before I get started to give you some context, I don’t like buying soil components. I don’t know about you, but I have enough junk to store. No matter what you do when you make your own mix you’ll inevitably not use all of all of your components and thus have to store extra bags, and these bags are big. Instead of carefully measuring these out, I suggest you tailor what you make based on what you’re trying to accomplish and what you have lying around.



  • potting soil
  • pine bark (or other bark)
  • perlite (just a touch)
  • spaghnum moss – great for root development
  • worm castings – for natural organic fertilizer

I roughly shoot for 25% of everything except perlite.  Just add a generous dab of perlite in (like adding a dash of spice to cooking), maybe 5% perlite.

Recall that soil mix components should add nutritional content to the plant and provide a place for the roots to grow securely.  Juicing up the potting mix aerates the soil (if you’re not sure what that means or why you want that try this article here) and gives it some extra nutrients to help get your trees to grow.



As I’ve outlined I have five components: potting soil, perlite, peat spaghnum moss, worm castings, and bark. I like to minimize the number of bags I have to store or the amount I waste so I choose bags based both on value for size, but also based on the size I think I’ll use.  You can find most of what you’ll need at your local nursery store.



Potting soil of any kind.


Cheap and easy to find. You can get an 8 quart bag at Home Depot and Lowes for just under $5.  Unless you’re a bonsai nursery is about all you need size-wise.


Also cheap and easy to find. I picked up a regular old 8 quart bag at Home Depot for just under $5 as well. Also Miracle Gro, though I have no product loyalty here. Keep in mind you’re looking for PEAT spaghnum moss. There is another kind of spaghnum moss for orchid planting. It’s frequently sold in brick like form, whereas the peat moss you want is in a dirt-like consistency. Peat spaghnum moss will lighten your soil and is good for root development.


A little goes a long way with worm castings. It can be concentrated so read the package to see what concentration level you’ve bought and adjust your mix accordingly. If you’re using worm castings for other areas in your yard you might want to go bigger. Otherwise, something like this earthworm fertilizer would work. It’s just under five pounds for around $13.


To find pre-bonsai soil components, bark is the most complicated.  Of your bonsai soil mix components pine bark (or bark of any kind) is one of the cheapest, if you don’t care about quality or size.  That’s the thing.  If you want the good stuff you can absolutely buy pine bark fines from Bonsai Jack (see here). And it’s fantastic. It’s sieved and cleaned (a couple times) and looks gorgeous.  The same way people put coffee beans under those big coffee urns at a fancy party, this would be fantastic to put under green tea to catch the drips.  You just want to dig your hands in it.  But that level of quality isn’t necessary for potting soil.  Mixing Bonsai Jack pine bark fines in with potting soil would be a bit like mixing your Johnny Walker Black with Coke.  Just don’t do it.  Save it for your real bonsai soil mix.

This post is a bout making PRE-bonsai soil. Modified potting soil, if you will. If you want your bark dirt cheap (pun completely intended), you’re skipping quality in terms of rounds of cleaning and sieving.

Your alternative to sexy perfect bark is going to your local garden shop.  If you were looking for pine bark, it’s likely the first thing you’ll find is bark chunks the size of your palm.  Or “mini” chunks the size of half your palm.  Or cypress “shredded” bits the length of your ring finger.  Which logistically just won’t work.  Some of the preferred terminology can be asking for bark “fines” or “soil conditioner.”

When I find a bonsai hobbyist that uses bark for pre-bonsai soil mix, I ask where they get it.  Where they get it is all over the place.  One from a local nursery, the next from Walmart, the third from Lowes, sometimes other sources too.  I’ve tried to track down a product before, so for example I pulled out a smart phone and hopped online and asked them to identify the picture of the bag they have.  Trying to get the actual product has never once worked for me.  I’ve gone into my local Walmart or Lowes and showed them the picture or read the title of the product to be told they don’t have it.  I’ve called and asked for “soil conditioner” to be told they don’t have it.

Online I’ve seen the discussion too, which has gone something like “EXACTLY where do you get your bark?  Show me a link to the product or give me the name of the product and the store you buy it from.  I’ve seen links to big box sites that are no longer good, and people who can’t get the product in question from their local store.


I’m guessing that because bark is cheap, and big box stores may have different suppliers based on where across the country the store is located, and they may change their inventory based on the time of year (more in spring than winter perhaps).  One branch of a chain may have something another does not, and one store may have something now that they won’t in six months.  I’ve also heard reports of bonsai lovers using a product regularly only to find one day that their source changes their product.  As in they bought the same bag with the same title from the same place and the new material is different.  Understand whatever local product you find today may be gone tomorrow.  And anything online is going to cost more due to shipping.

That said, my advice is to wing it.  You’re looking for ballpark size pieces, not perfect sexy material.

With any of the big packages is you usually can see through the package, but you can’t touch the product.  Can’t sieve it through your fingers.  As far as I know there is no standard by which the word “shredded” or “mini” is within a set size range. That leaves you to peer at what you can see through the plastic bag.  Above are some pictures from my most recent trip to the store.  If I stick away from the large nuggets my options are “natural” mulch from citrus and eucalyptus, cypress blend, and “red mulch” which didn’t have a lot of information on exactly where the material was coming from, the focus was more on the color.


The above picture on the left shows a comparison of rough bark from a two cubic foot bag I picked up at a big box store on the left, and some gorgeous Bonsai Jack bark on the right.  The image on the right size is a closer look of some bark from the big box store the other day.  Bark ranges hunks the size of your palm to looking almost like dirt.  I bought this bark in my hand here and am using it for my next mix.

As a side note, bark releases nitrogen as it ages.  So ideally you don’t want to use fresh stuff. This is where being lazy actually pays off. I just buy it a bit in advance and let it sit around for awhile before I mix it.


Pine vs something else?

Mulch options may cover a variety of species.  Does it matter if you use pine rather than fir, cypress, cedar, or other woods?  Are they all the same?

No, they are not all the same.  Different kinds of woods differ in water retention and rate of decay.  (I’ve also heard there’s also a difference in the propensity of some kinds of woods to be more susceptible to virus and fungi.

Pine bark is popular not only because it’s widely available (and usually relatively cheap), but because both the time it takes to decompose and store water well.  You want components that hold water until your tree can use it, yet not block oxygen reaching the roots.  Part of why bonsai soil looks like a bunch of tiny rocks and gravel is because those tiny rocks provide air pockets.

I also heard one person suggest you can plant bonsai in absolutely anything as long as it gets the nutrients, water, and oxygen it needs.  So what should you use?  If you have a choice and all prices were the same, go for pine, fir, or sequoia.  Pass on the cedar, cypress, and anything that’s defined by the color of the mulch.  This is just your amped up potting mix, but only you can say if a lesser material works for your purposes.


Reptile / Hamster bedding?

When your looking around online and you’re looking for clean bark of a certain size, there is the option of using reptile bark.  The leading brand is Repti Bark by Zoo Med, and it’s a fir bark.  It’s a bit of an in between solution.  The bark is cleaned and screened for size, and it’s about half the price of the best stuff.  But it’s also lots more expensive than big box store mulch which is frequently in the $3 for two cubic foot price point (ball park).



Bark releases nitrogen as it ages so ideally you don’t want to use the fresh stuff. This is where being lazy actually pays off. Just buy it a bit in advance and let it sit around for awhile before mixing it.


I like to mix my pre-bonsai soil in a large storage bin. Layer all the components in there like a lasagna.  Then mix it up, snap on the lid and viola!  You have a large bin of amped up potting soil.  You might see in the picture a cat litter bin.  The last time I did this I stored the finished soil itself in a couple cat litter bins and used the large storage bin for leftover soil components, storing the two cat litter bins on top, because that just works for my storage space.  You’ll also see my executive plastic cup to use to scoop the soil.  There isn’t any reason to use your good bonsai scoops on this stuff, so here I’m using an empty cookie cup which I rescued from the recycle bin and has served me well.

With that, you have your new and improved potting soil.  With this batch ready to go I’m now ready for spring.

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