Top layer rocks

[Krone]

What kind of material/rock is appropriate for the top layer of the bonsai substrate?
I am talking about the decorative/aesthetic top layer of the soil, it you would want to do that.

 

[TomB]

Akadama or dark-coloured lava

 

[Krone]

Akadama or dark-coloured lava

Thanks, i already know about these two.
But i want to know in more general sense. Which stuff should i avoid and why, what properties would be appreciated in the material, etc.

 

[Shibui]

You can use anything that looks good for the surface cover.
For developing trees it just needs to hold the surface in place when you water - does not really even need to look good. I don't usually bother with cover on developing trees as they are not on show and I water carefully enough not to wash away the soil.
On better trees consider the 'story' you want the bonsai to tell - desert, mountain, rainforest, mountainside or open woodland, etc. Then decide what ground cover would be appropriate for that tree. You could conceivably use a different type of cover on each of your bonsai to tell each tree's story properly.

 

[Krone]

Mostly i was wondering if some type of rocks can harm the bottom soil.
And yes, this top layer is meant for the developing trees. For the trees that are already in pots and are 'better' ones i use sphagnum moss / regular moss mixture.

Some of my trees are at my parents place where i keep the trees in development, collected ones etc.. But when i start to work on the tree i take it to my apartment. And because all of my trees are on my balcony i try to make them look as nice as i can (also keeps the GF happy.), event if they are still in training pots .

 

[Underdog]

I have used aquarium gravel (because I had it) to adds some weight and keeps the bark chips in the mix from floating away. It comes in a lot of color choices too. I believe it's granite from the weight of it. Cheap and readily available.
I've also used it for my dry creek bed in a forest.

 

[Shibui]

Mostly i was wondering if some type of rocks can harm the bottom soil.
And yes, this top layer is meant for the developing trees. For the trees that are already in pots and are 'better' ones i use sphagnum moss / regular moss mixture.

Some of my trees are at my parents place where i keep the trees in development, collected ones etc.. But when i start to work on the tree i take it to my apartment. And because all of my trees are on my balcony i try to make them look as nice as i can (also keeps the GF happy.), event if they are still in training pots .

I can't think of any natural rock that would be harmful to the soil. If there was such thing then noting would grow in the area where it occurs so we would see large areas devoid of plant life.
I would probably avoid limestone type stone as a topping for acid lovers like azalea. Not sure if the stone would release enough to affect the tree but safer is better than sorry.

Keeping GF happy is even more important that having the trees look good so definitely find some decorative stone. I see a few people using aquarium gravel. Looks good, a range of colors and relatively easy to get. Ironstone is popular here - dark color, heavy, usually consistent size and shape.

 

[rockm]

Top dressing is completely unnecessary and can be detrimental as it can wind up "channeling" water, instead of allowing it to drain directly into the soil. It's not a huge issue, but it can crop up. uniform soil mix from top to bottom in the pot is ideal.

 

[Krone]

Top dressing is completely unnecessary and can be detrimental as it can wind up "channeling" water, instead of allowing it to drain directly into the soil. It's not a huge issue, but it can crop up. uniform soil mix from top to bottom in the pot is ideal.

I can understand that but it's a training pot (large one) so i think that water shouldn't be an issue.

I have used aquarium gravel (because I had it)

Would assume that if it doesn't harm the fishes it also shouldn't harm the tree.

 

[rockm]

I can understand that but it's a training pot (large one) so i think that water shouldn't be an issue.



Would assume that if it doesn't harm the fishes it also shouldn't harm the tree.

It is a bigger issue for trees in training than established trees, particularly if those trees in training have been recently root-pruned. those trees need evenly supplied moisture in the soil. Overuse of top dressing can create drier spots in the soil and prevent moisture from draining through properly. Newly developing roots require Oxygen exchange as much as water. Water draining evenly through a uniform soil pulls in O2 more effectively...

 

[Leo in N E Illinois]

@Krone
seriously, @rockm is laying out the horticulture truth. Top dressings with materials that are dissimilar to the main potting mix will, not can, but will eventually cause problems. Doesn't matter the age of the tree, training pot or not.

Exception is the thin layer, less than 1/4 inch ( less than 0.63 cm) of shredded long fiber sphagnum moss, as top dressing, that is used for deciduous trees in shallow pots.

 

[Krone]

Thanks all. Have already decided against
Now i just have to figure it out what to do with large bag of aquarium basalt grit

 

[Carol 83]

Thanks all. Have already decided against
Now i just have to figure it out what to do with large bag of aquarium basalt grit

Get some fish