AusBonsai

, just wanted to ask a question about a DIY soil I'm experimenting with.

When we bought our house I inherited a big ugly pile of gravel under an old tarp. I gather it's the sort that you use to mix with cement when you're concreting. Anyway, till now I've been reluctant to use it, knowing nothing about what sort of gravel it is or whether it's ok for plants.

But on the weekend I made up a mixture, of about 1/3 chopped spaghnum, 1/3 ordinary garden potting mix, and 1/3 gravel. i sifted the small particles out of it all (using the kitchen strainer we use to strain the peas and carrots- don't tell my wife!)

I then potted up an sao-to-me azalea, bouganvillea and a little ivy. But, I'm just wondering whether people think that was a mistake. Do you suppose that sort of gravel could be in any way harmful?

I guess time will tell..

Hi Ben, Blue metal not at all mate especially if you have sifted the fines out !!! I would be more concerned about so much spag keeping the mix too wet for too long !!!

anttal63 wrote:Hi Ben, Blue metal not at all mate especially if you have sifted the fines out !!! I would be more concerned about so much spag keeping the mix too wet for too long !!!

Thanks for that mate. Blue metal? I'll have to read up on it. Very glad to hear that though. Too much spaghnum? Yes, it did feel wettish.. What would be a better percentage of spaghnum for a general use bonsai soil?

Yes I'd say it would be 1/4 minus.

I presume this could be and is called bluemetal as well.

ben the barbarian wrote:

anttal63 wrote:Hi Ben, Blue metal not at all mate especially if you have sifted the fines out !!! I would be more concerned about so much spag keeping the mix too wet for too long !!!

Thanks for that mate. Blue metal? I'll have to read up on it. Very glad to hear that though. Too much spaghnum? Yes, it did feel wettish.. What would be a better percentage of spaghnum for a general use bonsai soil?

To be honest i dont use spag in my mixes, only when airlayering !!! however i use diatamite, pumice,zeolite, that in this order from most to least all draw, hold and release moisture when needed.

thanks Boic and Ant

I haven't used spaghnum in a general mix either, only for layering also. But last week I read about the 1/3 gravel 1/3 soil, 1/3 spag in a Peter Chan book, so I thought I'd give it a try, seeing as though I'm often a bit neglagent with my watering I thought a bit of extra moisuture might be just my poor ol' plants are after!

ben the barbarian wrote:thanks Boic and Ant

I haven't used spaghnum in a general mix either, only for layering also. But last week I read about the 1/3 gravel 1/3 soil, 1/3 spag in a Peter Chan book, so I thought I'd give it a try, seeing as though I'm often a bit neglagent with my watering I thought a bit of extra moisuture might be just my poor ol' plants are after!

When the weather is hot and dry im sure its great but what about the rest of the time ??? And even if you allow the pots to dry out between waterings, 1) that needs to be monitered dilligently 2) there is still the problem of when it rains days on end or humidty is really high.

The BIG question nagging at me here is what is the stone size? Until we know that, the rest is incidental. Or is it?

Andrew Legg wrote:The BIG question nagging at me here is what is the stone size? Until we know that, the rest is incidental. Or is it?

fair call Andy !!!

Andrew Legg wrote:The BIG question nagging at me here is what is the stone size? Until we know that, the rest is incidental. Or is it?

It's pretty fine.. I'd say about the size of kitty litter? Maybe 5mm diameter?

ben the barbarian wrote:

Andrew Legg wrote:The BIG question nagging at me here is what is the stone size? Until we know that, the rest is incidental. Or is it?

It's pretty fine.. I'd say about the size of kitty litter? Maybe 5mm diameter?

perfect !!!

(1/4) inch = 0.635 centimetres

Therefore it would be 1/4 minus stone.
Often used in building.

Cool, thanks for the info. I'm glad that I can make some use of the big ugly pile! More than enough for a lifetime of bonsai!!

My basic bonsai mix is:

30% blue metal
30% pumice
30% potting mix (with fines sifted out)
10% course sand

Depending on my tree species or where it is at i change the grade of the aggregate size or the mix slightly. I go out and buy bags of blue metal 5-7mm and pummice 4-10mm. Even though this is the size it states when you sift it out (i use 5mm+, 3-5mm and 1-3mm) you end up with a hell of a lot more 3-5mm than anything else with the next big makeup being 1-3mm so i find these the perfect bags to buy. The 5mm+ i use for my big trees that are not so much bonsai yet but are dug out of the ground or in the process of reducing from 100L pots etc so in my mind this gives the ideal growing conditions for fast root development while i am hacking at the tree etc...

My trees that are forming more i use the mid size mix to allow for great root growth but at a reduced rate and then for my one tree that is in the ramification stage i use a mix of the 3-5 lower in the pot and then the 1-3 on the top part of the pot.

So in short... no problem using the blue metal from my experience!

Ben,

Key here is understanding the mechanics of soil particle size and the requirements of your different bonsai species. The smaller the particle size, the more moisture it will hold. The larger the particle size, the more air it will hold. So, for a small particle size mix you need less additives to hold moisture and for a larger particle size mix you need more water-holding additives. The moss is essentially a water holding additive, so for trees that prefer wetter growing conditions, add more, and for trees that prefer dryer growing conditions, add less. You'll need to factor in your climate as well, so the hotter and windier it is where your trees grow, again, the more moisture retention you need in your mix.

Next thing to add is something that provides "food" for your trees. Traditionally a lot of us have added compost for this (which also serves to hold moisture), but there are growers that feed through watering only. If you are diligent, there is a lot to be said for this method as well. Sphagnum moss is not going to add much to the feeding of trees, so you either need to add compost or water with food. Your choice.

Hate to say this, but you gotta do the sums mate!

Cheers,

Andrew