The ''Drainage Layer'' a misconception.

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The ''Drainage Layer'' a misconception.

Postby treeman » August 9th, 2017, 1:38 pm

Many articles such as this one....
http://bonsaiwonders-art.blogspot.com.a ... ayers.html
have been written regarding the myth of a 'drainage layer'. So here I would like to help clear things up a bit.
The ''Drainage Layer'' is a coarse layer put into the bottom of the pot before adding our planting mix. ( the ''main soil'') The whole problem with the confusion stems from the fact that the term was probably a misrepresentation or a wrongly translated idea from Japanese Bonsai growers by Western writers.

The so called ''drainage layer has absolutely nothing to do with drainage. As has been demonstrated countless times with sponges etc; a saturated area remains at the bottom of the pot after watering. This is because the capillary action is interrupted. Below the pot there is air. There is nothing to pull the water out of the pot as there is in the field. The excess water is held there by surface tension. That means that with a uniform mix throughout the pot, there is less available air at the bottom of the pot compared to higher up. In other words, air filled porosity is decreased in that zone. Whether this become a problem is governed by many things including the size of the tree in relation to the pot, the speed of evaporation, the type of tree etc. It may be preferable for some trees to do away with this coarse layer to give the tree more available water were most of it's roots are concentrated. For example I would suggest that many Paper Barks would do better without it whereas Leptospermum laevigatum would probably benefit.

In the early days, most bonsai were pines and junipers, and these types certainly need to be protected from a waterlogged condition.
Using a coarse layer at the bottom of the pot is designed to restore the air filled porosity or, if you like, mitigate the saturation in that zone NOT to improve drainage. That is why it continues to be advised by professional bonsai growers in Japan. It is extra insurance when trying to preserve a valuable tree. So when you read ''drainage layer'' from now on, think ''aeration'' layer instead.
Be your own judge as to whether you need this layer in your pots but be aware that it is used for a specific reason and the reason is not drainage of water.
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Re: The ''Drainage Layer'' a misconception.

Postby Piscineidiot » August 9th, 2017, 3:54 pm

Interesting subject. Was just listening to Ryan Neil talk about just that on one of his mirailive videos. I wonder if the roots that form in highly oxygenated, but saturated soil differ in any way to roots that form in oxygen-poor, saturated soil of the same particle size?
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Re: The ''Drainage Layer'' a misconception.

Postby treeman » August 9th, 2017, 4:03 pm

Piscineidiot wrote:Interesting subject. Was just listening to Ryan Neil talk about just that on one of his mirailive videos. I wonder if the roots that form in highly oxygenated, but saturated soil differ in any way to roots that form in oxygen-poor, saturated soil of the same particle size?


I'd like to see that. Where do I find it?
I think submerged roots are different but not sure if that is the case in a medium. The roots in a saturated medium would be weakened and vulnerable to attack by pathogens which thrive in that environment. It seems that's not the case with totally submerged roots for whatever reason. You can strike a cutting in water but the same thing would rot in a poorly aerated soil.
Last edited by treeman on August 9th, 2017, 4:09 pm, edited 1 time in total.
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Re: The ''Drainage Layer'' a misconception.

Postby treeman » August 9th, 2017, 4:39 pm

I should have also added that the coarse layer will take more time to fill with roots thereby delaying repotting. Once full of roots the aeration layer ceases to function and it's repot time.
Does any one have a Japanese White Pine on it's own roots? How is it going and do you use an aeration layer?
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Re: The ''Drainage Layer'' a misconception.

Postby Piscineidiot » August 9th, 2017, 5:00 pm

It's the "Repotting Fundamentals" video:

https://live.bonsaimirai.com/archive

Might have to join up to see it. I've found it worthwhile to sign up, but I don't have your years of experience, so any new information is good information.

Back on the subject of soil - to play the devil's advocate:

If a coarse layer on the bottom actually prolongs saturation of the root ball (which is detrimental), why even have it in the first instance?

Are those roots able to use the oxygen diffused into the water, or is gaseous oxygen what they require? If gaseous oxygen is in fact what they need, then surely it's more appropriate to create an environment where there is NO standing water?

(I don't necessarily agree with what I've typed, but I'm trying to follow a line of logic)
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Re: The ''Drainage Layer'' a misconception.

Postby Piscineidiot » August 9th, 2017, 5:07 pm

Come to think of it, I think I can answer my own question.

The way we avoid creating a saturated layer for an unacceptable amount of time is:

"Watering correctly"

Guess it just drives home the fact that we can't just water willy-nilly, even when we have a free-draining mix. It's still important to give the tree just enough, and not too much.
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Re: The ''Drainage Layer'' a misconception.

Postby wrcmad » August 9th, 2017, 5:20 pm

Piscineidiot wrote:Interesting subject. Was just listening to Ryan Neil talk about just that on one of his mirailive videos. I wonder if the roots that form in highly oxygenated, but saturated soil differ in any way to roots that form in oxygen-poor, saturated soil of the same particle size?

I recently watch this vid as well.
He said it is a misconception to call it a "drainage layer", as the substrate should be free-draining enough without it, but rather should be called an "oxygenation layer", which allows oxygen to fill the porous gaps and assist in diffusing up into the root system. The philosophy is that you don't really want the substrate to "hold" more available water to the detriment of root health - rather, his solution is to water more often.

Piscineidiot wrote:Are those roots able to use the oxygen diffused into the water, or is gaseous oxygen what they require? If gaseous oxygen is in fact what they need, then surely it's more appropriate to create an environment where there is NO standing water?

(I don't necessarily agree with what I've typed, but I'm trying to follow a line of logic)

As far as I understand, roots need oxygen in gaseous form.
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Re: The ''Drainage Layer'' a misconception.

Postby KIRKY » August 9th, 2017, 5:42 pm

I have a few Japanese White Pines on their own root system (not grafted). I have all of them in a cactus mix with the aeration layer. Todate I have had no problems with them. Watering is controlled by me with no extra from rain or drizzle.
Therefore they are kept on the dry side especially in winter when soils here in Melbourne can be continuously wet.
In summer they are still under the eves and are watered exactly the same as all my other trees.
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Re: The ''Drainage Layer'' a misconception.

Postby shibui » August 10th, 2017, 8:19 am

Drainage layer was also traditionally used in Western potting AKA 'crocking' where stones or broken terracotta was placed in the bottom of pots before adding the potting medium This was partly to stop the soil falling out the holes much like we use mesh in bonsai pots but it was also reputed to provide a place where water could drain out of the mix.
This practice started to disappear when we moved on to soilless potting mix and is rarely used now. I think that's because modern mixes are far better aerated and drained that the old soil and clay based mixes.
It is interesting to note that plastic pots with 'water well technology' are becoming popular in the nursery industry. They are designed to hold a shallow layer of water in the base. Seems to be the opposite of improved drainage but alos seems to be working with modern potting media.

We have moved quite quickly to far more open mixes for our bonsai which, depending on your chosen mix, has far greater AFP and draining capability than those used even 20 years ago. I seem to be having success without an 'aeration' layer in my bonsai pots and will continue not to bother until someone can convincingly demonstrate a better way.

My white pines are only 4 year old seedlings, still in deeper nursery pots but seem to be healthy and growing without a drainage/aeration layer so far. Time will tell.
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Re: The ''Drainage Layer'' a misconception.

Postby Gerard » August 10th, 2017, 9:32 am

My practice has been a little different, my potting mix is expensive and I am in the habit of reclaiming most of it after repotting. Very large pieces are reclaimed and used as an aeration layer in my orchid pots for trees which I am growing on. Established trees in bonsai pots always get a mix of new soil.
What I have learned (for the orchid pots with reclaimed soil) is that I get very fibrous roots in the upper layer but less roots in the aeration layer. This gives me a nice shaped root structure to be potted into a more shallow bonsai pot in the future. I suspect a pot without the coarse layer would have developed fibrous roots throughout the pot and probably have stronger growth. I probably should reconsider my method.
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Re: The ''Drainage Layer'' a misconception.

Postby treeman » August 10th, 2017, 10:51 am

Gerard wrote:My practice has been a little different, my potting mix is expensive and I am in the habit of reclaiming most of it after repotting. Very large pieces are reclaimed and used as an aeration layer in my orchid pots for trees which I am growing on. Established trees in bonsai pots always get a mix of new soil.
What I have learned (for the orchid pots with reclaimed soil) is that I get very fibrous roots in the upper layer but less roots in the aeration layer. This gives me a nice shaped root structure to be potted into a more shallow bonsai pot in the future. I suspect a pot without the coarse layer would have developed fibrous roots throughout the pot and probably have stronger growth. I probably should reconsider my method.

Those orchid pots have so many holes I find the bottom part tends to be avoided if you use too coarse a mix at the bottom because they dry out so fast there. I now use fibre glass fly screen to line the bottom before filling them. Then I can use a slightly finer material without it falling through.
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Re: The ''Drainage Layer'' a misconception.

Postby treeman » August 10th, 2017, 11:06 am

He said it is a misconception to call it a "drainage layer", as the substrate should be free-draining enough without it, but rather should be called an "oxygenation layer", which allows oxygen to fill the porous gaps and assist in diffusing up into the root system. The philosophy is that you don't really want the substrate to "hold" more available water to the detriment of root health - rather, his solution is to water more often.


That's exactly right.

Piscineidiot wrote:Are those roots able to use the oxygen diffused into the water, or is gaseous oxygen what they require? If gaseous oxygen is in fact what they need, then surely it's more appropriate to create an environment where there is NO standing water?

(I don't necessarily agree with what I've typed, but I'm trying to follow a line of logic)

As far as I understand, roots need oxygen in gaseous form.


Oxygen ''dissolved'' in water is still in a gaseous form. Not bonded to the H2o therefore freely available.
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Re: The ''Drainage Layer'' a misconception.

Postby Lane » August 12th, 2017, 4:50 am

Interesting topic, I will run some experiments.
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Re: The ''Drainage Layer'' a misconception.

Postby Bretts » August 13th, 2017, 7:29 am

The ''Drainage Layer'' is a coarse layer put into the bottom of the pot before adding our planting mix. ( the ''main soil'') The whole problem with the confusion stems from the fact that the term was probably a misrepresentation or a wrongly translated idea from Japanese Bonsai growers by Western writers.

Exactly, the article explains the concepts very well but then totally misses the point by just assuming why it was done. I call it drainage manipulation.
It amazed me so many so called experts went along with this myth busting.
Nice work Treeman.
Last edited by Bretts on August 13th, 2017, 7:30 am, edited 1 time in total.
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Re: The ''Drainage Layer'' a misconception.

Postby Damian Bee » August 13th, 2017, 10:32 am

Great topic.

I have sometimes used this layer, and sometimes not used it depending on several things.
The species grown/size of specimen, the type of pot/size of pot, the medium used, the amount/availability of medium in use, climate and perhaps the results of the last effort with similar ingredients.

If I am using a layer, it is now usually a 10mm grain at 20-25mm thick for smaller pots/containers and for larger a 30-50mm layer of 20-40mm material. I hold the layer into the pots by using anything from nothing but it's physical ability to stay put to disposable nail gun belts to pot mesh, it has always come down to availability of time and resources.

The reason I put a layer of coarse material into the base of pots is based on the fact that my shelves/surfaces are never level and the bottom of most containers is not draining in a even manner, I figure that I can avoid water pooling and the resulting problems that can come with it.

I have seen instances where I have repotted Satsuki and found masses of roots in the layer of sand in the bottom of the boxes soaking up the air and moisture and layers filled with muck from the use of sketchy mediums which has made the exercise of using the layer pointless.

My thoughts on what it really does in a container environment are a little foggy but I do believe it assists making more oxygen available via draining to a small extent as the particle size allows excess water to fill the air pockets between and then move out of the pot all together with the exception of moisture held initially after watering the mix due to surface tension and ponding in the bottom of the container, use of a free draining mix does negate a lot of these factors though, remembering that as you water a free draining mix, the water pulls fresh oxygen through with it as it moves downward through the container. What Shibui mentioned about waterwell pots being more popular in commercial growing is true, these type of pots must be used with a specific mix in mind to allow the absorption and retention of moisture to supply the plant grown in it, amazing what a long drought and economic rationale can do.

It's one of those methods which is based on personal choice. I use it if I have time, no harm done so far (after many years of trial and error :whistle: )
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