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[JKD]

It’s also a key feature of turf design. This is an explanation from: https://www.turfdiag.com/perched-water-table/

Perched Water Table

The USGA system provides maximum removal of water during heavy precipitation events, and it stores water above the gravel during periods when the ground is not saturated. How does it achieve this effect? Because the USGA system is based upon a concept known as the perched water table, which is also known as an inverted filter design. It is called an inverted filter because of the presence of the fine sand particles over the more coarse gravel. This design allows water to be held (or perched) in the rootzone layer. This perched effect occurs because the primary driving force for water movement during periods of unsaturation is the capillary effect of the particle voids.

The large voids of the gravel result in a reduction in the capillary effect. At the rootzone/gravel interface, these larger voids effectively create a barrier to further downward water movement during unsaturated times. As saturation is approached, additional pressure is applied allowing water to move into the larger voids of the gravel layer, and further down through the sub-surface drainage system.


And a couple of .edu resources specific to perched water tables in containers.

Rocks in Pots: Drainage or Perched Water Table Problems?

Many of us have grown plants in pots, planters or other containers. It’s a different environment. Not only is the planting location unique – isolated from the ground and open at both the top and some on the bottom, the container soils are different from ground bed soils. The soil’s most...

lee.ces.ncsu.edu

The Hard Truth about Rocks at the Bottom of Planting Containers | Nebraska Extension

By: Kathleen Cue, Nebraska Extension Horticulture Educator As we get our containers ready for planting our amazing annuals or that coveted tomato plant, conventional “wisdom” dictates we must first add an inch or so of gravel. Problematic? You bet! Rocks in the bottom of containers do not...

extension.unl.edu

A soil scientist explains in video if you prefer:

 

[KIS]

Am I looking at the “Clay Layer” below the “Perched Water Table”.

Do you perched water table people go outside?
Your pseudoscience ain’t helpin anyone grow better weed.

It has nothing to do with the layer being clay. It's any 2 dissimilar layers or materials. Just because you don't believe it doesn't make it any less factual or true. The science is very clear on this topic and there's plenty of information to support how this happens in the ground and in containers. I hope folks will do there own research.

 

[X15]

It’s also a key feature of turf design. This is an explanation from: https://www.turfdiag.com/perched-water-table/

Perched Water Table

The USGA system provides maximum removal of water during heavy precipitation events, and it stores water above the gravel during periods when the ground is not saturated. How does it achieve this effect? Because the USGA system is based upon a concept known as the perched water table, which is also known as an inverted filter design. It is called an inverted filter because of the presence of the fine sand particles over the more coarse gravel. This design allows water to be held (or perched) in the rootzone layer. This perched effect occurs because the primary driving force for water movement during periods of unsaturation is the capillary effect of the particle voids.

The large voids of the gravel result in a reduction in the capillary effect. At the rootzone/gravel interface, these larger voids effectively create a barrier to further downward water movement during unsaturated times. As saturation is approached, additional pressure is applied allowing water to move into the larger voids of the gravel layer, and further down through the sub-surface drainage system.


And a couple of .edu resources specific to perched water tables in containers.

Rocks in Pots: Drainage or Perched Water Table Problems?

Many of us have grown plants in pots, planters or other containers. It’s a different environment. Not only is the planting location unique – isolated from the ground and open at both the top and some on the bottom, the container soils are different from ground bed soils. The soil’s most...

lee.ces.ncsu.edu

The Hard Truth about Rocks at the Bottom of Planting Containers | Nebraska Extension

By: Kathleen Cue, Nebraska Extension Horticulture Educator As we get our containers ready for planting our amazing annuals or that coveted tomato plant, conventional “wisdom” dictates we must first add an inch or so of gravel. Problematic? You bet! Rocks in the bottom of containers do not...

extension.unl.edu

A soil scientist explains in video if you prefer:

Ok I understand where your thoughts are with that. I understand USGA Green complex and Green construction… pretty damn good actually. As I graduated from OSU and studied Turf Science very thoroughly. I have also been a golf course superintendent for a number of years and have worked at a number of course all with a wide variety of soil profiles. I’ve built many greens and understand the effects warranted in a perched green complex.
BUT IN NO WAY IS A GREEN COMPLEX LIKE A POTTED PLANT WITH SOME ROCKS IN THE BOTTOM. Guys you keep forgetting about the fact the pots have a number of drainage holes in the bottom and fabric pots are a whole different situation. I’m not saying I put rocks in the bottom of my pots, but i will say that telling someone they shouldn’t bc of this and that is just wack. There’s a lot more that can make or break a grow and it won’t be bc of some rocks in the bottom of a pot.

 

[X15]

It has nothing to do with the layer being clay. It's any 2 dissimilar layers or materials. Just because you don't believe it doesn't make it any less factual or true. The science is very clear on this topic and there's plenty of information to support how this happens in the ground and in containers. I hope folks will do their own research.

Again. A clay layer and a rock layer are going to have two completely different effects on water movement through the soil. And after all I thought we were talking about you guys hating on rocks in the bottom of pots. Shouldn’t we be trying to Keep it Simple?

 

[JKD]

From the bit about turf that you have experience with:

“The large voids of the gravel result in a reduction in the capillary effect. At the rootzone/gravel interface, these larger voids effectively create a barrier to further downward water movement during unsaturated times.”

Same as a pot with rocks.
Barrier to further downward water movement during unsaturated times means the water isn’t reaching the drainage holes because it remains perched above the gravel.

It’s used in turf because it’s beneficial to have good drainage when it’s raining, and a water reservoir when it’s not - the turf depth prevents problems with root rot as it’s >18”.

In containers it can cause problems due to their limited height because the roots are more likely to sit in the perched water.

Watch the vid, good explanation and demonstration - or better still get a pot and see for yourself. Why is the soil wettest above the gravel if the gravel is improving drainage?

Agree with you about there being bigger issues for a newb, but also lets help them avoid problems like root rot.

 

[X15]

From the bit about turf that you have experience with:

“The large voids of the gravel result in a reduction in the capillary effect. At the rootzone/gravel interface, these larger voids effectively create a barrier to further downward water movement during unsaturated times.”

Same as a pot with rocks.
Barrier to further downward water movement during unsaturated times means the water isn’t reaching the drainage holes because it remains perched above the gravel.

Watch the vid, good explanation and demonstration - or better still get a pot and see for yourself. Why is the soil wettest above the gravel if the gravel is improving drainage?

Agree with you about there being bigger issues for a newb, but also lets help them avoid problems like root rot.

Peat can only handle so much water Bud. Coco too. They don’t hold water like native soils do.

 

[X15]

From the bit about turf that you have experience with:

“The large voids of the gravel result in a reduction in the capillary effect. At the rootzone/gravel interface, these larger voids effectively create a barrier to further downward water movement during unsaturated times.”

Same as a pot with rocks.
Barrier to further downward water movement during unsaturated times means the water isn’t reaching the drainage holes because it remains perched above the gravel.

Watch the vid, good explanation and demonstration - or better still get a pot and see for yourself. Why is the soil wettest above the gravel if the gravel is improving drainage?

Agree with you about there being bigger issues for a newb, but also let’s help them avoid problems like root rot.

Esp with the use of warring agents or.. Either via irrigation or by pre treatment. The quality of your coco or peat makes a big difference. The use of biochar and compost makes a big dif. Calcium levels will affect hold capabilities as well. There are a number of factors. 10” of water penetration is much different than 10’ or 100’ in the ground.
Rocks in the bottom will reduce your over all soil volume but. Simply put. The more rocks the less soil right? More rocks doesn’t mean WATER TABLE.

Edit: Wetting*

 

[JKD]

I can see you’re very committed to your position.

I hope that anyone else reading this who still has doubts will take a little time to fill a pot with a layer of gravel, followed by soil, or turf, or coco, or peat etc. After watering the mixture and allowing it to drain, easily observe the phenomenon by digging down to the gravel layer.

This is the path I took, because for many years I added a ‘drainage’ layer.

When I learned about perched water tables (via delta9nxs & his PPK ) I didn’t initially think it made sense. Rather than dismiss a counterintuitive new idea (to me), I made a small effort to learn and understand the theory of it. Even then, I still wanted to see it for myself, so I did my own little experiments. In a couple of hours I went from not having heard of it, to being dubious, to understanding it, to observing it, to accepting it. It’s that easy to set aside our assumptions, and what we think we know, to confirm for ourselves.

If you use gravel or leca etc, why is the mix above it always wetter? Why is it the bit that falls of the rootball? People using a ‘drainage’ layer would have already seen it’s effects and maybe just not given it any thought - as was the case for me.

A thorough 'Water movement in soil' demonstration from Washington State University:





I've occupied too much of this thread already.

Have a good one X15.

 

[KIS]

I can see you’re very committed to your position.

I hope that anyone else reading this who still has doubts will take a little time to fill a pot with a layer of gravel, followed by soil, or turf, or coco, or peat etc. After watering the mixture and allowing it to drain, easily observe the phenomenon by digging down to the gravel layer.

This is the path I took, because for many years I added a ‘drainage’ layer.

When I learned about perched water tables (via delta9nxs & his PPK ) I didn’t initially think it made sense. Rather than dismiss a counterintuitive new idea (to me), I made a small effort to learn and understand the theory of it. Even then, I still wanted to see it for myself, so I did my own little experiments. In a couple of hours I went from not having heard of it, to being dubious, to understanding it, to observing it, to accepting it. It’s that easy to set aside our assumptions, and what we think we know, to confirm for ourselves.

If you use gravel or leca etc, why is the mix above it always wetter? Why is it the bit that falls of the rootball? People using a ‘drainage’ layer would have already seen it’s effects and maybe just not given it any thought - as was the case for me.

A thorough 'Water movement in soil' demonstration from Washington State University:





I've occupied too much of this thread already.

Have a good one X15.

Thanks JKD, saved me from responding. Folks can read both positions and do their own research. "You can lead a horse to water but you can't make them drink!"

 

[X15]

Thanks JKD, saved me from responding. Folks can read both positions and do their own research. "You can lead a horse to water but you can't make them drink!"

Yeah and a Horses olfactory system is roughly 100 times greater than Humans…
Which might conclude that the Horse isn’t going to fall for the humans Bullshit lol.