article: A durable bonsai substrate as replacement for akadama and peat

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A durable bonsai substrate as replacement for akadama and peat 

Substrate in stead of soil

The term substrate offcourse implies it is mainly composed of inorganics. More than 5 years ago, after thorough reading and researching all kinds of sources, substrate was the choice I made. I will not elaborate on the pros and cons of mainly (approx 50% and up) organic soil, I can however share the main reason why I do prefer inorganics: Total control. I consider this a big plus if it comes to feeding and watering my trees. It is all about diminishing the risks, the ‘can-go-wrongs’. I know better how my substrate will behave, than I would with mainly organics. No more soil that contains too much salts, and the risk of getting the PH of my substrate all out of balance is lower too. No more rootrot in soaking wet and clumped soil.
Besides ‘total control’ there are offcourse a number of other reasons: I no longer depend on akadama, I now use more durable (no peat, no turf) compounds, my main compound has better properties than akadama on many aspects, it is more affordable, it does not break down,...

Durable alternative for peat and akadama
Most brands of potting compost still rely on peat or turf. Peat mining has significant environmental impacts. Mining to date has opened up extensive areas of swamp with an extensive free water area now replacing what was a shrubland/rushland peat deposit. Damaged swamp filtering function, damaged ecosystem, destabilization of hydrology, etc. Swamp areas with peat deposits carry/are one of the most specific habitats. If I can replace peat or turf with an equally good (or better) more durable alternative, I happily use this alternative. This is why I use cocopeat for the organic part in my substrate (max. 20%). It is a byproduct, it does not break down as fast, and it is a good water and nutrient absorbant.

Besides peat-based soils, most bonsai enthusiasts use akadama-based soils. For sure, one of the first things a beginner buys has got to be akadama. All shops I know of will advertise akadama as basic. Offcourse this is due to the fact that akadama is traditionally used in Japan. There was no need for westerners to ask questions, the use of this material was/is just copied, the akadama imported. That is all fine, but questions finally begin to rise due to the fact akadama gets more sparse, more expensive. For me personally, I just wanted to know if there were other materials that can do the job just as fine, or better, why not ask this question, why not learn lots of things while searching for alternatives.


My substrate formula

Natural zeolite (clinoptilolite) granulate, medium (2-5mm), depending on the size of the pot I’ll mix it with small (1-3mm) and/or big (5-10mm) to come to an overall 70 to 80%. The other 20 to 30% is cocos compost. This comes in rough bits of coconut bark and fibres, or in fine compost. The rough cocos I don’t use because I don’t have huge sized pots nor do I have pines (only 1 shohin). Depending on how thirsty my (broadleaved) tree is, I’ll mix the 20 or 30% cocos. The more smallsized particles of zeolites, the more moisture your substrate will be able to hold. This very simple and basic substrate mix I’ve been using for several years (since 2010) with satisfying, good or very good results.

Easy watering, easy feeding. When watering, water abundantly until it runs out from underneath the pot, overwatering this substrate is impossible unless you’ve used way too much cocos in combination with only the small zeolite granulate. U can use liquid chemical fertilizer but I prefer liquid organic fertilizer, in combination with 1 or 2 times organic fertilizer in granulate for hedges (that contains mycorrhizae spores).

What is akadama (and kanuma)?

Many enthusiasts (even sellers) hardly know what akadama (akadamatsuchi) actually is. In short: is a (clay-'like') mineral of vulcanic origin. Volcanic ash deposits from mount Fuji to be precise and therefor it is mainly mined in the Kanto region, e.g in prefectures like Tochigi or Ibaraki which several will know because it is a very famous akadama brand. Mining takes place at selected areas, where the black topsoil rich in organics is first scraped off to find the directly underneath 'reddish' layer from wich akadama comes. Because of the colour (its rich in oxides) akadama is also called red ball earth. The mined red ball earth is dried to a higher/lesser extent to get the desired hardness, and processed to get different granule size.

Because of all this volcanic activity, several layers have accumulated on top of each other, from different eruptions. Kanuma for instance is nothing more than the layer underneath akadama, from the explosion of mount Akagi. It is more yellowish and has different composition/characteristics.

Now, zeolite is also a volcanic mineral, again with different composition/characteristics. So with this in mind (volcanic minerals) it does not make sense not to want to compare substrates.

My current substrate formula

Because I’ve found new studies/info about crop growth in pure zeolite substrate, indicating an initial strong growth followed by a decline or stagnation in ‘strong’ growth (sheer biomass production), I decided to re-evaluate or update my substrate mix. In all studies however, zeolite proves to be a highly effective growth and root stimulator, along with other advantageous characteristics (more below).

I use 3 different things: zeolite (main part), lava, and coco(peat) in always the same parts per volume. I don't really 'tune' my substrate, I 'play' with the same ingredients, in case of very small pots (very very low pots also fall into this category) or in case of superthirsty species like alder (alnus glutinosa). Then I just tune the grain size, e.g. more 'small' zeolite in the zeolite fraction. You get the picture.

The mix in the table underneath is usable as standard mix for all broadleaved trees, based on Zeolite (main part). The small granulate makes sure enough moisture can be retained. For very big pots, or pines/spruces I suggest you vary the granulate size of your compounds (more big grain vs small), but do not 'exclusively' use the biggest size for all 3 parts of your substrate and for instance try to compensate with higher organics.

Compound	Remarks	Parts per Volume
1.       ZEOLITE (= clinoptilolite, preferrably the 95% pure, or else the 80-85%)	Medium size for most pots, vary for small or big pots (or do a mix of small-medium in your zeolite part)	2/4
2.
3.       Lava (or bims)	different kinds available, choose lava for gardening purposes (or ask for PH values if you buy at pond/aquatic stores). I use the 1-3mm size (brand: DCM kleigrondverbeteraar)	1/4
4.       Cocopeat	I use cocopeat (brand: Ecostyle, BIO), it even has a bit of gray lava sand mixed in.	1/4 'maximum'
Optional: Dried cow manure pellets	= oil improver, not fertilizer In substrate, it helps to bring in essential bacteria faster. The fertilising aspect of cow manure is very low to unexisting.	1 handfull

Lava

Because lava is wellknown, I will not elaborate on them any further. The only thing I could point out it is that there are several types of ‘lava’: gray, brown (like pozzolane), black, small, coarse,...
Ask for PH value if you buy at aquatic store, and check if the lava has been washed. Up to you to decide if you also want some pumice in your substrate or not, in the mix with the lava part or even as a replacement. This will not really make a huge difference. The small lava fraction I find very convenient, in colour, in adding weight, adding smaller particles to surround the soil with and yet not loose the aereating function.

Zeolite (natural clinoptilolite)

There are many many types of ‘natural’ zeolite (do not use synthetical zeolites as they don’t carry micronutrients and tend to break down in prolonged acidic environments, eg when u do want to decide to use chemical fertilizer). Clinoptilolite is one of these natural zeolite, and perhaps the most commercialized and the one that is most used for horticultural purposes. In Belgium and the Netherlands it is marketed by some companies who import it, either from within the EU or from outside the EU. The clinoptilolite that is mined in Romania, Bulgaria, the Tchech Republic, Hungary, Armenia, Greece, is less 'pure' and 'contaminated' with other minerals like quartz, feldspar… . The most known companies that market it in Belgium and the Netherlands is about 80 to 85%. In the past however, I have obtained bags that contained 95% pure clinoptilolite. I suspect this comes from the Turkish mines. The reason why these the 95% now doesn't seem to be imported any more (for the time being?) is mainly for commercial reasons according to me: it contains a bit of dust, not desirable for marketing as soil for birdcages, catlitter soil, etc. In bonsai this is not a problem, 2 or 3 waterings and its gone. Another reason may be the legal and administrative issues for importing from outside the EU. I've also been told a mine is said to have ceased production.

What's so special and good about zeolite, even the 80-85%? The main reaons:

• A very high CEC (cation exchange capacity), reaching as high as 170/180meq/100gr (meg=milliequivalent). This is 5 or 6 times higher than akadama (source: colinlewis, amongst others). All values above 25 are considered good soil CEC. The higher, the richer in nutrients your soil is/can be. CEC value expresses in technical terms the capacity of soil/substrate to extract cations from water. Cations mainly come from metals, are positive charged and therefor are attracted by the negative charged zeolite. Zeolite happens to be one of the few natural negative charged minerals. In horticulture the cations considered are Fe, Mn, Zn, Cu,...
  Theoretically, because of this high CEC fewer fertilising is needed because less of the administered fertilizer will leach out with effluent.
• A honeycomb microporous celstructure. This means zeolite has a huge 'surface' area, as much as 60 square metres/gr (for the 85%). This structure allows water/nutrients be buffered/released on demand, in high degree. It also creates a good surface for colonization from useful bacteria and even mycorrhizae.
  
• A usefull side-effect of the high CEC is that zeolite is capable of neutralising (permanently buffer) harmfull ammonium, nitrate.
• To ensure you can profit from these beneficial characteristics, one advice: do not fertilise very aggressively, don't mess up your PH. If you do, your bonsai will pay the price. Be carefull with too much chemical based fertilizers, use mainly organics and in prescribed dosage. Remember the high CEC and don't try to 'boost' that still further. If you over-fertilise, like in all soils, you will also kill any mycorrhizae

 

Cons of Zeolite?

• ·         Allthough it makes your soil or substrate peat-free (peat is - still – a very basic compound of most compost soils, it is more and more contested because it is not durable and because of the drastic ecological impact), zeolite equally is a mineral that is mined, so there still is a certain ecological impact.
• ·         The colour of the 80-85% pure zeolite is not very attractive/esthetical as topsoil covering in bonsaipots (offwhite or offwhite with few earthcolour speckling, and a light bluish when saturated). This can easily be solved by covering the topsoil with a separate mixture of the other compounds of the substrate described above, eg lava + bims.
• ·         eTo get your hands on zeolite: google is your friend, it can be a shorter/longer quest. There are also greenroof applications with zeolite, like 'Clinopti' or 'Vulkagran-T', other horticultural substrates are 'Pon' and 'Vulkagran'.
• ·         Zeolite is quite heavy when fully saturated. But then again, lava also is.