How to Mix Your Own Bonsai Soil
Introduction to Soil
Bonsai is a hobby that anyone can enjoy. It’s often a hobby people pick up to get in touch with nature if not themselves. As discussed in my Beginner’s Guide to Bonsai, anyone can bonsai by meeting a few conditions. Anyone new to bonsai or to any hobby tends to have many questions. Quite often, however, the new hobbyist asks all the questions but the really important ones. How much wire do I need to buy? How much water is too much? What kind of style is most attractive for every tree? Can I bring the tree inside to display indefinitely? How fast will this grow? I need to make sure this tree grows super quick, what can I do to make this tree grow senselessly?! Passion for a new hobby can be like falling in love and it’s easy to let a spark grow into a flame and then into an inferno. It’s important to know that with any new hobby, the hobbyist should be open to suggestion and do what’s logical and proceed with caution and reason. We often overlook the very obvious things even when doing tasks we do every day. Why I stress asking the right and important questions is because I was one of those who overlooked such obvious issues and didn’t ask the important questions. I’d like to rectify my sin and pass on to new hobbyists the importance of starting from the ground up, literally!
What’s so dang important? In my opinion....Soil. That’s the most important aspect to bonsai and often we disregard it because we perceive a tree as a tree and soil is soil. Therefore, anything should work. Soil is more than just digging up a clump of dirt in the yard and putting it into a pot and saying: “we’re done with step 1, let’s move on.” Because soil is such a great component when it comes to repotting bonsai trees. It's important to understand why repotting a bonsai tree is a necessary evil and why we do so. Part of being in the bonsai hobby is being a little bit of everything: i.e. horticulturist, geologist, artist, etc. What one is trying to do is to replicate nature and nature has been at this game for a long time so it’s safe to say “imitation is the sincerest form of flattery.”
Soil vs. Substrate
Soil used in bonsai is a very widely debated issue due to every hobbyist having their own recipe mix for their soil. One person’s soil composition for tropical trees may be too light or too heavy for a different hobbyist's tree. Some people will even mention that bonsai soil is not even soil at all as it can contain no soil in the traditional sense. Many people will prefer to call their bonsai substrate “mixes” to back away from actually calling it soil to mitigate confusion. Regardless of what you use for any tree, the real difference between the traditional sense of soil and bonsai mix is that drainage is optimal and the main goal to achieve.
Why is Drainage Important?
Why is drainage key to growing healthy bonsai? You can ask yourself "If that’s my only concern, I’m sure it can be solved by my pot having holes, I’m sure it will drain regardless how what's in the pot and how much water it has in it, right?" Well, that logic is not entirely wrong because a hole will release any fluid in time. But that's another contingency, and the time it takes water to leave the soil and pot is solely dependent on the medium of the bonsai soil mix. Of course allowing water to drain quickly will spare the tree from suffering “wet feet” which leads to root rot. You are welcome to place a tree into a densely packed pot of soil like potting soil mix or the soil you dig out from the ground; however, you might not have a tree that’ll be as healthy as a tree placed into efficiently draining soil. So try to imagine, through time as soil starts to compact, how will air and water will permeate through the soil? Starving roots from oxygen can result with roots not growing properly which will result in weak trees that will not allow the tree to be secured properly.
Without being informed that bonsai soil is not really soil, would you have known that there was a special type of soil mix specifically for bonsai?
What Are the Components?
Bonsai mix can be separated into two categories, Organic and Inorganic. The difference between organic and inorganic is based on water retentiveness. Both ingredients have grit which allows for excess water to drain from the mix. But aside from that, the names for both are literal as organic components have decaying plant matter; while inorganic ingredients are comprised of no organic matter like rocks and other gritty material like baked clay. Unlike days of the past when baked clay was not as readily available, organic matter was more favorable. However, traditional mixes were a danger to the possibility of over watering and a dramatic shift towards inorganic matter is now on the rise. In modern times, growers who use a mix of high fired clay and other gritty material that are great water retainers; yet, coarse enough to encourage root growth, can water multiple times a day without over watering. There are some growers who grow their trees in pure baked clay for maximum water drainage and maximum oxygen permeability. But should be cautioned loose mixes can disrupt root growth due to shifting.
Organic components comprise of conifer bark, peat moss (humus), potting soil and any other composted material. To go into further detail:
- Conifer bark as a soil conditioner can add bulk to the mix and can retain moisture; while allowing excess water to drain.
- Peat moss (humus) is what retains the most water and therefore should be used sparingly. This material is really used just to bind the material together so the different components do not shift around as roots are growing. It's important to know moss can hold a substantial amount of water and without proper drainage, it can hold onto a large amount of water for a long time.
- Potting soil will add bulk to your mix as well as used as a bonding agent. Be aware potting soil is highly water retentive.
- Decomposing plant matter is added as feed.
The key to inorganic components is to add "grit" to a mix. The more grit you add the more aeration it allows and that will help stimulate strong root growth. Inorganic components consists of other materials that do not break down like the organic counterpart. Most inorganic components are highly prized for their porous properties that can retain water but does not break down as quickly or condense. Here are various types of inorganic components:
- Akadama: this is a hard fired clay and great at retaining water. This component is ideal for mixing bonsai soil. It is often considered to be a mandatory component when creating your bonsai mix. The only problem with this is it will break down in a few years.
- Turface: this looks a lot like the high fired akadama clay but it isn't. This material is mainly used for the underlining of golf courses and baseball fields as it does wonders of allowing air to penetrate; thus, making it perfect for grass.
- Lava rock: this material is incredibly coarse and porous. Unlike the other two mentioned before, this component will not breakdown as easily. People like to use this as a top dressing for their gardens, but have no idea how incredibly great this serves as an aggregate in bonsai mixes.
- DIATOMACEOUS EARTH: This material is a bit out of the ordinary and is only advised should you not find anything else mentioned on the above list. Diatomaceous earth aka Oil Sorb or Oil Dri, is used by mechanics who spread the stuff onto the floor in case of oil spills. The material will soak up the oil and will make clean up a lot easier. In bonsai it works in the same principle, it will soak up water and retain moisture but still hold onto it's coarse shape allowing roots to grow around it. If you are able to obtain this stuff, make sure to confirm the material is #8822. This is tried and tested and will not turn to mush.
Additional Soil Conditioners
The different components mentioned above is only a little of what can be used in bonsai. There are various other soil conditioners and soil aggregates that can be used in mixing your own bonsai mix. The important factor to know is will your addition provide the three goods:
- good aeration
- good drainage
- good moisture retentiveness
These should be the three guidelines to consider when adding other components to your mixture. Some may be conventional and some may be out of the book suggested by a person whom you trust knows that works. You just have to try it yourself to confirm and conduct tests. One can not go wrong with either organic or inorganic components, just as long as it provides those three things.
The Right Equipment
Component aside, the right equipment will allow you to get the best out of your material. When talking about equipment, I mean a sifter. Your material, which will come in bags or sacks will have a lot of impurities and those impurities can range from dust, to just various other nasty things that you don't want. For example, you'll want to get rid of dust as dust can settle and clog holes through time. Other impurities like grass and possibly other organic matter can do the same type of damage. Sifters will allow you to sift the material through various levels which will allow you to have smaller granules for smaller potted bonsai to larger granules for larger bonsai. Sifting is not necessarily an important step; however, it is highly and sometimes strongly recommended because you paid a lot of money for your material, why not take the additional step.
As mentioned above, there is no one way to approach your own unique mix. There are a few guidelines that many can suggest but be aware that they are just suggestions. As a hobbyist in bonsai, it's important to be open minded and try it your way before dismissing or criticizing. What may not work for you will work for someone else. As there is a clear guideline for various types of bonsai, mixes will have to correlate to match the specific types of trees.
Bonsai Mix Recipe
Basic Bonsai Mix
Tropical Bonsai Mix
Deciduous Bonsai Mox
Conifer Bonsai Mix
Lava rock/Diatomaceous earth
Organic Compost Component
Clump vs. Loose
Naturally, after a period of time, soil will condense and that condensing action will be simulated to test how well your soil will hold up. To simulate that type of compaction, even before you fill the pot with your bonsai mix, you should be able to squeeze a big clump of whetted mix in your hand. If the mix compacts and stays like a very dense hard clump, your mix is too full of organic matter and will retain a lot of moisture. This can lead to a lot of problems, for example, root rot can happen when roots are kept in moist soils for a long period of time. Also, air can't penetrate the soil thus causing more problems. Should the mix fall away after you release it from your palm, you have a good well draining mix. To correct either too lose or too compact, simply add to the mix of either more grit or more organic matter to fit your needs.
Mixing your own bonsai mix is a great sign of dedication. Your love for your tree starts from the ground up. Mixing your own bonsai mix will allow you to understand your tree a lot more. A tree will often be able to tell you how it feels and will let you know what its needs all based on its mix condition. A good mix will allow the grower to know when the tree needs water and the condition of the tree. A good mix can determine how much training a tree can endure this year. A bad mix will result with a delay in growth and as well in health. A sick tree is limited in what it can do and often times, the grower's simplest demands are all too much for the tree. Take care of your tree by giving it the best soil mix you can muster. I never asked the stupid question until late in the hobby, I hope this comes to you early in your journey as this is an important aspect to bonsai.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.