General soil mix recipes

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General soil mix recipes

Postby massia » April 5th, 2018, 2:57 pm

Looking for a general soil mix recipe, I’ve read about a lot of different recipes for soil mixes for repotting and ended up buying: Akadama (2-4 mm), pumice and lava rock (4-8 mm).
Some say that I also needs fertilizer and compost. What’s your take on this?

I have both deciduous trees and pines and read that the general mix could be
Deciduous: 50% akadama, 25% pumice, 25 % lava rock
Pines: 33% akadama, 33% pumice, 33 % lava rock

Does that seem right?

Thanks for the help! 
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Re: General soil mix recipes

Postby shibui » April 5th, 2018, 9:02 pm

You can grow bonsai in almost any mix. Every bonsai grower will tell you about their special mix that is far better than anyone else's but is there really any real difference?
Personally I use the same mix for all my bonsai. I know that all pots will drain and water the same. I know fertiliser will be consistent over all the pots. I know that the mix in all pots will age and last the same in all pots. It also saves me having 2 lots of mix and components taking up space.
I think all my bonsai do pretty well in the same mix.
All potting mix with organic components must have some fertiliser because the organics tie up nitrogen as they decompose and several other nutrients can be tied up or leached out. With your inorganic mix you may be able to get away with just using regular added fert but I find that I tend to miss occasionally. Controlled release in the mix will give a steady release of nutrients and make up for my erratic application and I think it is definitely worth including just before potting up.
Compost is not all the same. Good compost can enhance the CEC (cation exchange capacity) which will hold nutrients for the plant. I'm not sure what CEC you will get from akadama, pumice and lava. It is likely that nutrients will leach quite quickly from that mix. That's Ok as long as you can replace nutrients regularly. Poor compost will introduce weeds and may even tie up nutrients. It also tends to be hard to re-wet if the mix dries out. add compost if you wish but it is not essential.
You can grow bonsai in almost any mix when you adjust conditions to suit the mix.
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Re: General soil mix recipes

Postby treeman » April 6th, 2018, 1:33 pm

massia wrote:Looking for a general soil mix recipe, I’ve read about a lot of different recipes for soil mixes for repotting and ended up buying: Akadama (2-4 mm), pumice and lava rock (4-8 mm).
Some say that I also needs fertilizer and compost. What’s your take on this?

I have both deciduous trees and pines and read that the general mix could be
Deciduous: 50% akadama, 25% pumice, 25 % lava rock
Pines: 33% akadama, 33% pumice, 33 % lava rock

Does that seem right?

Thanks for the help! 


Your first mix (for deciduous) is too bony for them in my opinion. Especially for Australian conditions. Add some coco peat, peat, matured compost or similar.
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Re: General soil mix recipes

Postby massia » April 6th, 2018, 3:20 pm

@shibui: Thanks again for your help. It is much appreciated!
First of all – good idea with using just one mix! :-)
You write that organic mixes must have fert, but that inorganic must have “regular added fert”. What’s the difference (forgive me being slow). Is I understand your reply, I can “relax” more with compost added to the mix, since adding fert to an organic mix as not as crucial as adding it to an inorganic mix.

If I stick to my inorganic mix, is a workaround solution perhapse to fert using slow release fert in baskets or directly in the soil?

Where do you buy “good compost”? At your local garden center? And how do you know the compost is good?

Can I ask you what mix you use yourself?

@treeman: Thanks, as shibui also write, I can see it is worth considering.
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Re: General soil mix recipes

Postby kcpoole » April 6th, 2018, 5:38 pm

I have used inorganic mixes for about 15 years now and use the same in all my trees Except Azaleas where Kanuma 100%

Used to be 2 bag Diatomite, i bag zeolite
Now is bag each of Diatomite, Zeolite, Akadam and Pumice.

I fertilise every few weeks with liquid ( miracle grow or Charlie carp) and put a handful of Neutrog "Sudden Impact for Roses" on the top of the subsrate. I find this lasts fro about 6- 8 weeks then repeat

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Re: General soil mix recipes

Postby Paul W » April 6th, 2018, 8:37 pm

Agree with shibui,everyone has their own favorite mix and get very emotive over them,there are many threads on here about potting mixes,do a search on them and then do what works for you.start off with a good quality potting mix and add a bit of this and a bit of that,we get curl grubs here in Aussie land so it pays to put a bit course rough stuff in the mix as it hurts their bellies. :lol:
Bretts used to give a good debate on here about potting mixes,but he is very quiet on here of late. might have got in strife with the mods. :worship:
Last edited by Paul W on April 6th, 2018, 8:39 pm, edited 1 time in total.
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Re: General soil mix recipes

Postby dansai » April 7th, 2018, 7:06 am

Being from Denmark you are going to have very different growing conditions than we do in Oz, particularly if you are growing indoors for a large chunk of the year. Things like how often you can water will affect what type of fertiliser you could use and how components of your mix will perform. My place I water most days even in winter as my grow area is very sunny and has plenty of air movement.

Although you have been given sound advice here, it would be highly beneficial for you to seek out a grower near you that has similar growing conditions that can give you sound advice more specifically for your situation.
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Re: General soil mix recipes

Postby shibui » April 8th, 2018, 6:30 pm

Organic based potting mix must have fertiliser added before you put trees in it. That fertiliser is to counteract the nitrogen drawdown as the organic parts start to decompose. After planting you still need to add fertiliser regularly because watering tends to wash away any soluble nutrients and that's what the plant needs.
Inorganic mix does not need base fertiliser because it does not decompose but still needs fertiliser after planting to replace nutrients that are washed out of the pot by watering so not really much difference in the end.

Slow release fert in baskets can work but you need to be sure the fertiliser has all nutrients and trace elements (complete fertiliser). Note that many 'slow release' fertilisers are not complete fertilisers. They may not have all the nutrients and trace elemnets that plants need. I would still try to add extra every few weeks - soluble fertiliser is easiest to mix and apply.
Controlled release fertiliser (Osmocote is one brand here, you may have other brand names) mixed into the potting mix before you plant the tree is a good way to ensure your tree is getting constant low dose of background nutrients.

Dansai has a good point about fertiliser and frequency of watering being linked. Fertilise more often when watering frequently and less when not watering the pots very often.
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Re: General soil mix recipes

Postby The Munt » April 9th, 2018, 8:24 am

Sorry for Hijacking, but Shibui just came very close to answering a question I only half got to the bottom of...

I notice you mentioned mixing controlled release fertiliser into the soil, if you are repotting a Bonsai with this soil, it is fair to assume you may have trimmed the roots prior.

Someone told me recently you should steer clear of liquid fertiliser for a couple of weeks after root work, so my question is.. does that only apply to liquid fertiliser, if so is it safe to use controlled release fertiliser, just like Seasol or will that potentially harm the damaged root system too?

I'm guessing no, but my OCD needs to hear it! :lol:
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Re: General soil mix recipes

Postby shibui » April 9th, 2018, 5:41 pm

There is still a strong body of growers who advise no fertiliser for a few weeks after root pruning. I'm not so sure. As you have noted, trees potted into mix containing osmocote will get some fertiliser after the first or second watering. I have always used osmocote in the mix and have never noticed any adverse reaction to it immediately after repotting. This may be another of the old tales that have been handed down without anyone ever questioning whether it is correct.
I can't see any good reason why fertiliser would harm a recently root pruned plant any more than any other plant but I still generally wait a few weeks before the first dose of liquid fertiliser.

You have also pointed out that the same people who warn against fertiliser on newly root pruned plants also advocate soaking freshly root pruned plants in seasol solution. I know seasol do not call that product a fertiliser but it does have some nutrients in it. Why are those seasol nutrients harmless while others are harmful?
I suspect there is room for some trials and research here :reading:
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Re: General soil mix recipes

Postby massia » April 9th, 2018, 7:36 pm

Thanks for all the input. The reason I’m not writing in a Danish forum or talking to Danish bonsai enthusiast is that there aren’t many around (another reason perhaps is that it brings some “exotic charm” to my bonsai quest :-) )
And I guess I ask a lot because of my background as an engineer. And I am most certainly not used to have multiple correct answers to the same question – how rude :-) :-) :-)

I’ll stick to my inorganic mix, water some more and put some controlled release fertilizer (5:5:5) on top.
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Re: General soil mix recipes

Postby treeman » April 10th, 2018, 11:11 am

shibui wrote:There is still a strong body of growers who advise no fertiliser for a few weeks after root pruning. I'm not so sure. As you have noted, trees potted into mix containing osmocote will get some fertiliser after the first or second watering. I have always used osmocote in the mix and have never noticed any adverse reaction to it immediately after repotting. This may be another of the old tales that have been handed down without anyone ever questioning whether it is correct.
I can't see any good reason why fertiliser would harm a recently root pruned plant any more than any other plant but I still generally wait a few weeks before the first dose of liquid fertiliser.

You have also pointed out that the same people who warn against fertiliser on newly root pruned plants also advocate soaking freshly root pruned plants in seasol solution. I know seasol do not call that product a fertiliser but it does have some nutrients in it. Why are those seasol nutrients harmless while others are harmful?
I suspect there is room for some trials and research here :reading:

There are 2 main reasons for not fertilizing after root pruning. The first is that up to 75% of feeder roots (those with root hairs) are cut off so the ability to extract water and nutrients is severely limited for a while. (Of course if we reduce the water applied to the plant - as we should - there is no need to add nutrients as the plant needs water to take them up and at this time all we need to do is give enough moisture so the stored carbohydrates in the plant can produce new roots)
The second reason is that in most mixes there is more than enough native NPK for at least one month of growth or more depending on the mix. Will adding nutrients ''hurt'' the plant? Probably not but they won't have much benefit either.
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Re: General soil mix recipes

Postby shibui » April 10th, 2018, 6:00 pm

And I am most certainly not used to have multiple correct answers to the same question – how rude
This seems to strike most new bonsai growers. Most of us expect to get one right answer - especially engineers and mathematicians but we are dealing with living organisms. Biology has very few 'correct' answers and lots of gradients of correct answers because living things are adaptable.

On second thoughts - would an engineer suggest there is only one right way to build a bridge across a river?
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Re: General soil mix recipes

Postby massia » April 10th, 2018, 7:27 pm

I think it has to do with all the guidelines, codes and rules. Roughly there is only one or very few path(s) to finish if you are to do the calculations on a bridge, if material and design is given. :)
But how nice it actually is to be out of the comfort zone...
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