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!
k2bonsai, thanks for the tips mate! Good to hear aboout your soil mix.
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
thanks Andrew, I'll research more into the food aspect- good advice.
