Drainage Layer?

[Bretts]

The funny thing is Jamie that article was the least biased account of this subject I had seen to date

[senseijames]

Hey there guys/gals, I can understand all this discussion in regards to water tables and tensions etc, but if ones plants are all healthy and growing vigorously and there has been no regimented system put in place regarding the soil mixes or drainage material, then ??? why should one change what they are already doing. What ??? are the benefits. ??
James

[Handy Mick]

Hi guys, I've always used a layer of pebbles in the bottom of my pots, because i thought it just stopped the holes clogging over a period of time and to introduce air to the roots easier. I was told this a long time ago and have just always done it, by the way I use soil and not diatomite or similar

[Bretts]

The benefit could be even better growth. Or maybe you can manipulate the growth in a way you did not realise you could? I have had trees take off twice as big as one sitting next to it. Both look healthy and unless I had the one showing that the tree could be doing much better I would have thought all was well.
I am trying to say you will never know if you don't give it a go.
I think understanding that you can move the water table around the pot however you like is going to be limitless in possible uses through the years!

Yep Mick I was always told to do it as well. Then everyone on the international forums started saying it hinderd drianage I like understanding the real situation of what it is doing!

[Handy Mick]

I can't possibly see gravel at the bottom of the pot hindering drainage at all, when we build retaining walls you should always have a layer of gravel (blue metal) over some ag pipe behind the wall for drainage, this is a requirement and a Australian standard, this gravel layer keeps the back of the wall dry or allows the wall to dry faster, there for stopping your timbers from rotting. Not only that, but it is also to keep excess weight off the wall as well.

[Glenn C]

James, none at all if yours are doing well, but interesting just the same.

Brett, thanks, I will read this again when I've had some sleep.
I work with an ex ag scientist, he's been very handy teaching me about ion exchange, organic colloids, etc I will ask him about your salt build up.

[Bretts]

I can't possibly see gravel at the bottom of the pot hindering drainage at all, when we build retaining walls you should always have a layer of gravel (blue metal) over some ag pipe behind the wall for drainage, this is a requirement and a Australian standard, this gravel layer keeps the back of the wall dry or allows the wall to dry faster, there for stopping your timbers from rotting. Not only that, but it is also to keep excess weight off the wall as well.

The point is that the coarse layer will not suck the water from the finer layer above. The coarse layer around the agpipe ensures that the water in that area passes lower but it does not suck the water out of the soil above it. So the coarse area will stay dryer but techniclay it causes the soil above it to be wetter.

[Gerard]

I think most of this discussion has revolved around the suggestion that a layer of coarse material will raise the water table.
Perhaps this is correct but surely the amount of water in this "water table" will be greatly reduced.
I almost always use a drainage layer of scoria because I believe that too much fine material around the drainage holes will restrict the amount of water which can drain freely.

[Handy Mick]

This is all to technical for me, i'm just a lonly carpenter who likes Bonsai, not science.

[Bretts]

I think most of this discussion has revolved around the suggestion that a layer of coarse material will raise the water table.
Perhaps this is correct but surely the amount of water in this "water table" will be greatly reduced.
I almost always use a drainage layer of scoria because I believe that too much fine material around the drainage holes will restrict the amount of water which can drain freely.

Not necessarily Gerard
I guess you understand that a flat pot drains less than a tall pot. The problem is that raising the water table makes it a flatter pot. This is explained in both articles. The actual change is something for some one with better physics maths than I

[Bretts]

This is all to technical for me, i'm just a lonly carpenter who likes Bonsai, not science.

Like I siad I won't knock that Mick. There is plenty of info on what works some just like to understand why

[Handy Mick]

Thanks for the info Bretts, I do like to know the in's and out's, some times i just need to read twice for indepth info.

[alpineart]

I dont and have never used a drainage layer as such, the climate in Japan is a little different from where i live , but then i have never used a bonsia medium and i always water with a hose not a sprayer or a watering can with the nozzle upside down .God forbid if some guru turned up at my place .No bonsai mix , no bonsai wire and no bonsai watering can , just happy healthy trees in pots it works for me . Cheers Alpineart

[Deemon]

Hey Brett,

I've done a lot research on this topic myself, (I have a headache.)
I'm of the opinion now, that if your growing on in larger pots then more care is required with the drainage!

But in the bonsai pot, if like Walter Pall, (I know your a fan), you use a primairly open inorganic free draining mix, water and feed lots,
you won't have a problem! As Walter says, The results speak for themselves!

I think I remember reading him saying, no drainage layer, the medium is the drainage layer.

Works for him...

[63pmp]

I think the question about whether you do or don't use a layer is more about semantics than how well a plant grows, after all, they seem to grow well without a gravel layer. But more knowledge gives more optoins.

Brett,

from fear of starting another "discussion" I think your idea's about CEC and salts are a little off. Firstly, CEC in potting mixes is a bit of a myth, I say this because CEC is very much dependedant on particle surface area. The CEC calculations for zeolite are all done on powdered material, not on granules. So the CEC of zeolite is many orders smaller than what is talked about. Salts collect in potting mixes due to inefficient watering. Enough water has to pass through the potting mix to dissolve any salts and then flush them out. This may take several litres of water, simply as some salts are not very soluble. When watering with only a small amount of water being used, then salts will accumulate. CEC is a negative electrical charge on a soil particle, the cations are only loosely bound to this surface in a kind of cloudy mass. Those cations on the surface are more tightly bound then those away from the surface. Different cations have different sizes due to water molecules stuck to the cation. It is not so easy to remove these cations from the cloud, the exchanging cation must be small enough to worm its way into towards the particle surface, thus displacing a outer cation, or the concentration must be high enough to displace ions by mass force. All the same, CEC doesn't cause salt build up, this occurs in the outer soil solution. CEC of organic material is pH dependant due to the type of molecules in the organic matter, full CEC charge occurs when the potting mix is strongly alkali, it is almost non existent at pH of 5. So even the ability of organic material to buffer is quite restricted in a narrow pH band.

I've had to keep this brief as I'm at work and restricted for time.

Paul