Bonsai substrate mix for dry climates.

[Ujjawal Roy]

Very new, but half the reason for my lack of success in bonsai has been my experimenting with making soils because, like you, I'm not able to purchase them.

Your crushed clay pots (terracotta?) will hold a little moisture, but probably not enough for once a day watering in a hot desert climate. You might try crushed brick along with it. Retains more moisture, but not as much as adding something like clay (akadam, turface, etc.), and will release it fairly slowly after it's been soaked thoroughly.
Another idea is to use your pumice and the like- the porous substrates- but mix them with just a little very fine all-brown-matter compost (composted leaves, paper, bark, etc. but no food scraps or manure). It will rest in the pores of the stone, but get washed from in between the stones, and will help hold moisture, but never directly against the roots.

Otherwise, some very fine coco husk in limited quantities should do the trick, like you were thinking. I would say no more than 25% of the mix, but less if you're also using clay pots and brick.

Please let us know what works. I'm always on the hunt for ways to keep my hobby affordable.

I think it's red clay that's baked. Turface is restricted in my country and akadama is just too expensive for me.
The crushed clay pots soak up a good amount of water and if I break them while they are still wet, the inside if also dark in color.
Here, in India, people use lots of organics like compost, cow manure and all the other finer organic matter with red garden soil and maybe some perlite and sand but this mix gets compressed too quick for me and the roots start to rot. I've even seen stem rot on my trees due to such soil mixes. All this is so confusing. Help me, help!

 

[Ujjawal Roy]

Yes I use horticultural grade pumice.

When you water your bonsai, the water should immediately flow through the soil and out through the drain holes, leaving wet soil particles behind, but no standing water. If you water your trees, and the water appears to soak in (like a sponge), or worse yet, sits on top of the soil and has to slowly be absorbed, you need to repot and change out your soil. Yes, the top layer dries faster than the soil deeper inside the pot, but not enough to make a different (at least for me). It is a bigger issue immediately after repotting, but roots start to fill in the void spaces in the soil pretty quickly, and that will slow down the rate of desiccation.

Can you share photos of one of your stunted growth plants? Perhaps something else is at play.

The topmost leaf on my grapefruit and bougie ideally should be either of the same size or larger than the previous leaf but on both of these the topmost leaves have remained smaller than the preceding ones and it's been almost 5-6 days that they've not gotten any larger and that's puzzling. My bougie also dropped a newly growing leaf and you can see the scar on the terminal bud just above the newest leaves. Also, I have a ficus rumphii that is dropping new leaves, when the leaves are just about to open but they turn black, shrivel up and break from the petiole and I've seen a similar trend on my f. Religiosa as well. I have seen no pests whatsoever on them, no aphids, spider mites, milli bugs, nothing.

 

[Lumaca]

The topmost leaf on my grapefruit and bougie ideally should be either of the same size or larger than the previous leaf but on both of these the topmost leaves have remained smaller than the preceding ones and it's been almost 5-6 days that they've not gotten any larger and that's puzzling. My bougie also dropped a newly growing leaf and you can see the scar on the terminal bud just above the newest leaves. Also, I have a ficus rumphii that is dropping new leaves, when the leaves are just about to open but they turn black, shrivel up and break from the petiole and I've seen a similar trend on my f. Religiosa as well. I have seen no pests whatsoever on them, no aphids, spider mites, milli bugs, nothing.
View attachment 343700View attachment 343701

Isn't the goal of bonsai to reduce leaf size?

I can only speak from experience living in similar tropical condition, I think you are overdoing the drainage. You have a colander AND very gritty mixture.

Your plants are probably reducing leaf size to prevent moisture evaporation from leaves.

Honestly my plants in 50% lava and 50% organica wilt from 1 day of missed watering, so I don't think overwatering will ever be a problem in such high temp.

There were a few days when it was raining literally the whole day, so I thought I could get away with not watering the morning after, and I find my eucalyptus deglupta & lavandula angustifolia wilting. Then they perk up right after a good watering.

For what it's worth, I look at the locals for advice, and I get recommendations to use a mix of lava and compost. For certain plants they even recommend 100% goat poop!

 

[Ujjawal Roy]

Isn't the goal of bonsai to reduce leaf size?

I can only speak from experience living in similar tropical condition, I think you are overdoing the drainage. You have a colander AND very gritty mixture.

Your plants are probably reducing leaf size to prevent moisture evaporation from leaves.

Honestly my plants in 50% lava and 50% organica wilt from 1 day of missed watering, so I don't think overwatering will ever be a problem in such high temp.

There were a few days when it was raining literally the whole day, so I thought I could get away with not watering the morning after, and I find my eucalyptus deglupta & lavandula angustifolia wilting. Then they perk up right after a good watering.

For what it's worth, I look at the locals for advice, and I get recommendations to use a mix of lava and compost. For certain plants they even recommend 100% goat poop!

I'd have liked smaller leaf size had it been on a well developed tree that has an intricate branch structure and a proper canopy, but this lil guy is just a sapling and i want it to stay healthy. I'll keep watering the plant everytime the top soil looks dry.
I'm using this colander not for drainage but for air pruning. I have read that using a colander for growing saplings helps them to get a denser and more radial fibrous root system from the very beginning... I don't know if it works or not so I am trying it out for myself.

 

[Ujjawal Roy]

Yes I use horticultural grade pumice.

When you water your bonsai, the water should immediately flow through the soil and out through the drain holes, leaving wet soil particles behind, but no standing water. If you water your trees, and the water appears to soak in (like a sponge), or worse yet, sits on top of the soil and has to slowly be absorbed, you need to repot and change out your soil. Yes, the top layer dries faster than the soil deeper inside the pot, but not enough to make a different (at least for me). It is a bigger issue immediately after repotting, but roots start to fill in the void spaces in the soil pretty quickly, and that will slow down the rate of desiccation.

Can you share photos of one of your stunted growth plants? Perhaps something else is at play.

This leaf turned pale and broke off even before it could grow...

 

[eryk2kartman]

Whatever you use make sure you sift it and only use particles 2mm or bigger,
if you dont sift you will end up with way to much water retention and also limit the oxygen that is supplied to the roots.

 

[Ujjawal Roy]

Whatever you use make sure you sift it and only use particles 2mm or bigger,
if you dont sift you will end up with way to much water retention and also limit the oxygen that is supplied to the roots.

I'm shifting to using such soil which has particle size more than 3mm. When do you suggest I water the plant in this kind of soil? I mean should the soil be constantly moist or should I let the top 1/2" or 1" get dry then water the plant or how do I judge the watering need in such a gritty soil? Can such a substrate be overwatered if I water it once a day?

 

[eryk2kartman]

3mm is good particle size, yes soil will be very fast draining, you will have to experiment a bit and see how the trees react and take it from there.
In my personal opinion you cant over-water if you use 100% inorganic substrate,
I would start your watering routine from watering once in the morning, a good watering, i mean you water once, and come back 15 min later and water again and watch your trees and soil, if trees are showing lack of water, you need to water again.
Some of them might dry quicker than others, with high temps as you have i would say you will have to water at least twice per day.
Im in Ireland and during the summer months even temps are only around 20-25 C i have to water twice per day.
If you add some organic particles you will have to be a little bit more careful with watering.....
Watching your trees how they react is the best what you can do, maybe small diary to write down the results etc like time of the day, the amount of watering etc

Finding perfect soil mix is a trial error path until you get it 100% right

 

[Adair M]

Use a layer of spaghnum moss, the kind used for orchids on top of the inorganic soil. Don’t mix the spagnum into the soil mix, use it like a blanket on top. Water passes through it very well, but it is more retentive than the soil, and it will help the top portion of the soil stay moist longer.

 

[Ujjawal Roy]

3mm is good particle size, yes soil will be very fast draining, you will have to experiment a bit and see how the trees react and take it from there.
In my personal opinion you cant over-water if you use 100% inorganic substrate,
I would start your watering routine from watering once in the morning, a good watering, i mean you water once, and come back 15 min later and water again and watch your trees and soil, if trees are showing lack of water, you need to water again.
Some of them might dry quicker than others, with high temps as you have i would say you will have to water at least twice per day.
Im in Ireland and during the summer months even temps are only around 20-25 C i have to water twice per day.
If you add some organic particles you will have to be a little bit more careful with watering.....
Watching your trees how they react is the best what you can do, maybe small diary to write down the results etc like time of the day, the amount of watering etc

Finding perfect soil mix is a trial error path until you get it 100% right

Should I let my trees wilt a bit before subsequent waterings?

 

[Ujjawal Roy]

Use a layer of spaghnum moss, the kind used for orchids on top of the inorganic soil. Don’t mix the spagnum into the soil mix, use it like a blanket on top. Water passes through it very well, but it is more retentive than the soil, and it will help the top portion of the soil stay moist longer.

This might make it difficult for me to judge the moisture level of the actual substrate underneath the moss

 

[MrWunderful]

This might make it difficult for me to judge the moisture level of the actual substrate underneath the moss

Use your finger to move the same spot of moss everytime you check if it needs water. I use Akadama so I only need to look at the color about a 1/4” down (6mm?) hopefully you can use the terra cotta in same way.

 

[Adair M]

This might make it difficult for me to judge the moisture level of the actual substrate underneath the moss

If you use a good inorganic mix, you can’t overwater. So, water it if the spaghnum moss on top looks dry.

 

[Ujjawal Roy]

Use your finger to move the same spot of moss everytime you check if it needs water. I use Akadama so I only need to look at the color about a 1/4” down (6mm?) hopefully you can use the terra cotta in same way.

Thanks for the suggestion! I'll try doing that.

 

[Ujjawal Roy]

If you use a good inorganic mix, you can’t overwater. So, water it if the spaghnum moss on top looks dry.

Water doesn't pool in my substrate but it creates a muck on the lower layers of the pot where the roots start rotting eventually...

 

[eryk2kartman]

Are you sure you had i sifted? sound like small particles gathered at the bottom of the pot and probably blocking drainage holes.
when i water my trees, water comes out from the bottom in matter of second.
There should be no muck if it was sifted properly.
How deep is a pot ?

 

[Ujjawal Roy]

Are you sure you had i sifted? sound like small particles gathered at the bottom of the pot and probably blocking drainage holes.
when i water my trees, water comes out from the bottom in matter of second.
There should be no muck if it was sifted properly.
How deep is a pot ?

I had sifted the compost but after a few watering the balls of compost got washed away and broke down and got all mushy. But, again, that's compost... I don't like organics in soils. I am slowing transferring to usinh more inorganics, hopefully that'll prevent root rot in the future.

 

[eryk2kartman]

So lesson learnt, no more compost in the mix
You answered your own question why its waterlogged.

 

[hinmo24t]

If its super dry just add potting soil or more organic material thats available. Miracle grow cactus and succulent mix. Its potting soil w sand and perlite I think. This will stay wet longer than vermiculite clay and perlite for example

 

[eryk2kartman]

Vermiculite is really bad, it breaks down and creates a mush, its not good for bonsai