Drainage Rocks

[Jaws]

If I use bonsai soil, is it still necessary to put rocks in the bottom of the pot?

 

[shohin_branches]

If I use bonsai soil, is it still necessary to put rocks in the bottom of the pot?

Nope.

It's not necessary to put rocks in the bottom of a pot unless you're low on potting soil.

 

[SeanS]

It is generally a good idea to put a layer of coarser grain aggregate in the bottom of the pot for drainage. Usually a larger size particle of the same soil components (or one of them used in your mix) you intend using to pot the tree with.

 

[Deep Sea Diver]

Interesting. Of course one could not use a “drain layer”. Folks have all sorts of ways to try to grow trees.

But understand… it’s not really a drain layer. Using a layer raises the perched water level in a pot. This can be very useful. Using a layer can be helpful for those who understand the physics along with the effect of using different particle sizes.

If you would like to raise your knowledge level, try these @markyscott resources.

Resource one

Resource two

Good luck

Cheers
DSD sends

 

[Shibui]

@Deep Sea Diver got in ahead of me.
Drainage layer seems to be a carry over from the olden days of growing plants in pots. It may have originated as a way to stop all the soil running out the drain holes and I still use some rocks for that purpose in larger garden pots. Not necessary for bonsai pots as we have mesh to cover the holes to prevent the soil running out.

Drainage layer does not always enhance drainage. Theoretically it just raises the saturated zone higher in the pot. In deeper pots that doesn't really matter but in shallow pots that can create more danger for the roots.
Fortunately, theory doesn't always match practice. When we put finer particles on top of a layer of larger gravel those finer particles filter down into the larger gravel layer creating a mix of large and small. In other words, a 'drainage layer' just takes up space. It is just as effective to mix the larger gravel into your soil mix.
Even better, just leave out the larger gravel entirely and fill the entire pot with your normal soil mix. I stopped using a 'drainage layer' around 30 years ago. My trees don't seem to have suffered as a result.

 

[bwaynef]

For particularly shallow pots, Boon instructs to add large-grain pumice only around the drain holes, then fill in around that with whatever size soil being used for the rest of the pot. In some shallow pots, the health of the tree would be in jeopardy if an entire layer of soil were filled with drainage material.

 

[rockm]

A “drainage layer” at the bottom of pots is an old myth. It doesn’t work -see “perched water table”. It can actually keep top levels of the soil wetter for longer.

 

[Deep Sea Diver]

For particularly shallow pots, Boon instructs to add large-grain pumice only around the drain holes, then fill in around that with whatever size soil being used for the rest of the pot. In some shallow pots, the health of the tree would be in jeopardy if an entire layer of soil were filled with drainage material.

Interesting.

What does Boon say would the effect on the perched water table of only using larger media around the drainage holes? Totally understand the rationale of only using a very slim drainage layer in a shallow pot.

Cheers
DSD sends