can you overwater in mostly inorganic soil?

HazMatt

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ok, of course you can, but how likely is it?

the soil i have been using is mostly small lava (1/16"-1/8") with some perlite and DE mixed in. I am using about 20% sifted "cactus soil" to add some organic material, but its pretty minimal (the cactus soil also contains some perlite).

can you really overwater in this type of soil? I mean, you are pretty much getting air to the roots as soon as the water stops flowing... the soil is able to hold moisture for a couple of days right now, but the top 1/2" dries out pretty fast so i try not to let it go more than a day. temps are just starting to get high here (this week has been 80-90f). Summertime temps are usually high 90's to low 100's, occasionally getting into the low 110's. At that point I pretty much cant water enough...
 

Paulpash

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The larger the particle size the harder it is to overwater .... but harder to keep nutrients in the soil mix. I think I read somewhere that the ideal size is between a quarter to a half inch in diameter and has the capacity to act as a buffer. Have you read Walter's treatise on the subject?

http://www.youtube.com/watch?v=ccOGUj9b6dc&list=PL0B6A4EDA447A4BC6&index=1

Whether your mix is too retentive is very difficult for us to say but a few questions you need to ask yourself:

1) If you went to a totally inorganic, freer draining mix would you be able to supply your trees with enough water in summer (given job responsibilities)?

2) When you repot your trees - do your trees have a lot of fine feeder roots and no black fetid smelling gunky areas?

3) Related to 2 ... does water flow freely through your mix, injecting new O2 into the root system?

If the answer to 1 is yes then go down a grade. If no - stick as you are.
If the answers to 2 & 3 are yes then stick.
 

0soyoung

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You can.

Immediately after watering there will be a saturated layer at the bottom of the soil layer. The saturation layer is caused by capilation of water in the gaps between soil particles (smaller particles = thicker saturation layer). The saturated layer can only be emptied by the roots or by evaporation. If water is added too frequently, the saturated layer never goes away and roots in the layer will die/rot = overwatering.

My trees never have stinky roots - I use Turface MVP = totally inorganic soil. I used finer Turface proLeague for a time and found that my plants lived, but didn't have any roots in the bottom of the pots.

So called 'drainage layers' don't really drain anything. It is just using a larger particle size to have a shallower saturation layer under the tree and raising the saturation layer of your mix up from the bottom of the pot (not that there is anything wrong with it, but this is only what it does despite the name). Exending this idea, though, you can see that top dressing with a fine mix would keep the top of the pot wetter. The problem, though, is that the small partlcle top dressing tends to work down into the main mix instead of staying on top.

Top dressing with sphagnum is a popular top dressing for hot weather. Evaporation from a sphagnum top dressing also works as a swamp cooler; roots will not grow at soil temperatures above 95F.
 
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berobinson82

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You can.

Immediately after watering there will be a saturated layer at the bottom of the soil layer. The saturation layer is caused by capilation of water in the gaps between soil particles (smaller particles = thicker saturation layer). The saturated layer can only be emptied by the roots or by evaporation. If water is added too frequently, the saturated layer never goes away and roots in the layer will die/rot = overwatering.
Wouldn't that be alleviated by a drainage layer of more coarse particles?
 

coh

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And the large holes punched in the bottom of bonsai pots?
All I know is - after watering and allowing pots to drain, if I pick up and tilt the pots, there always seems to be more water that comes out...regardless of the number/size of drain holes. I'm sure more/larger holes do lessen the problem, though (and a drain layer may as well).

Have always thought it would be interesting to have a few glass or clear plastic bonsai pots so I could see exactly how much water remains in the bottom of the pots.

Chris
 

Dav4

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Here in the Southeast, I've found that many of my trees actually take a heat related dormancy in July and August. They stay nice and green, but actually pull less water from the soil. That, coupled with the high humidity typically found here during those months, keeps my 100% inorganic mix from drying out as quickly as it might in April or October. Mind you, the trees are typically only in direct sun from 11AM to 3-4PM, but my backyard is on a hill facing southwest and cooks when the sun is on it. So, yes, even in the heat of summer here in GA, I think it's possible to over water.
 

Anthony

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Ah but Dave4,

what happens when you add on wind to sun, as I have down here? chuckle.

To see how much water a bonsai pot will retain, just put some water in and see if the bottom is perfectly flat or imperfect or sloped to the drainage holes.

I have a snow rose [ Chinese ] growing in 100% crushed sifted red earthenware brick, and in a porous but glazed pot, just see what happens.
For 4 weeks it stayed green, but did not grow, and then I added a tablespoon of compost, sprinkled on the surface. I figure the compost should work it's was down and growth should restart sometime.
Good Evening.
Anthony
 

fourteener

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There are times in the year when the tree is using up less water. For me spring and fall rains mean daily watering is not needed.
Also over time the soil gets filled up with roots and slows the drainage.

Over watering is less likely to happen in a free draining inorganic soil. But every few years there are times in the spring when I have to put a chunk of 2X4 under the sides of all my pots to deal with too much rain.
 

FrankP999

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Wouldn't that be alleviated by a drainage layer of more coarse particles?
I have seen this referred to as "perched water table". See the illustration toward the bottom of this article http://oregonstate.edu/dept/nursery-weeds/feature_articles/physical_properties/physical_properties.html It comes about due to capillary action and the adhesion of water to the soil particles, which can generate stronger forces than gravity at the bottom of a pot.
 

markyscott

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Wouldn't that be alleviated by a drainage layer of more coarse particles?
And the large holes punched in the bottom of bonsai pots?
I have seen this referred to as "perched water table". See the illustration toward the bottom of this article http://oregonstate.edu/dept/nursery-weeds/feature_articles/physical_properties/physical_properties.html It comes about due to capillary action and the adhesion of water to the soil particles, which can generate stronger forces than gravity at the bottom of a pot.
The drainage holes allow the gravitational water to effectively drain, but the water held in the soil by capillary forces is held in the same way that water is held by a sponge. The saturation increases toward the base of the pot and is close to 100% saturated in a zone along the bottom. As indicated in FrankP999s reference, the shape of the pot and the size or number of the drainage holes do not impact the height of the saturated zone along the base of the pot. In a shallower pot, the saturated zone simply extends closer to the soil surface. The important variables are:

1) the grain size of the soil. Using finer-grained soils tends to increase the height of the saturated zone at the base of the pot.

2) the grain shape in the soil. Using rounded grains tends to decrease the height of the saturated zone.

3) the sorting of the grains in the soil. A uniform grain size tends to decrease the height of the saturated zone.

4) the drainage layer. This is more complicated as there are competing effects. First, the saturated zone in the soil will form at the top of the drainage layer, moving it to a higher elevation in the pot. A second, substatially smaller (see point 1), saturated zone will form at the bottom of the drainage layer. It sort of makes your pot effectively shallower. Second, the height if the saturated zone will be impacted by the difference in grain size between the soil and the drainage layer. A large difference in grain size will tend to increase the height of the saturated zone and a small difference will tend to decrease it.

5) time since watering and environmental factors. Over time, the amount of water held in the soil by capillary forces and the height of the saturated zone will decrease due to water being removed from the soil by the plant an due to evaporation.

Scott
 

Poink88

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Using a "wick" dangled through the drain holes will help you drain excess water and reduce your perched water table dramatically. If you decide to use it avoid ones made of organic material so they won't rot.
 

geoff hobson

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overwatering

I use a mix containing Akadama and Kyodama which is a gritty substance. I find that from around March to November I have to water then during December to end February I almost don't need to water, in fact there are times when it is necessary to tilt the pots to allow draining of excess water.
The use of inorganic or organic is not the problem, as long as the soil drains that is all that matters. I have used some composted bark in my mix and it still drained well, of course where you live and the temperatures will have an effect on evaporation along with wind. I have never used a drainage layer, and I don't know of anyone who does, it has no effect on water retention.
Each to his own, we all use the mix that we are happy with.
Geoff
 

Anthony

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Question to the responders-

Just how deep are thes pots you guys are using ?

I tend to have trunks maxing out at 3 inches, so 3 inches max. in internal pot depth, and only a very few cascade pots. Never had these situations of over watering.
Plus with full sun and wind, it helps to have soil that is moisture retentive. When the rains do return, the trees are most pot bound and can handle the extra water.

So is it my shallow pots that are preventing the over watering problem ? Or other ?

Thanks for any information.
Good Afternoon.
Anthony

* Plus, no winter, so I can use glazed but porous pots as well.
 

Beng

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I use medium to large coarse pumice in the bottom of my pots. I still get the dripping if I tilt a pot.
 
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Beng

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Those are some good looking roots, look at all that mycorrhizae!
 

Brian Van Fleet

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No, I use whatever I have that wont go through my biggest sieve. Mostly lava rock, haydite, and the last of some big (medium) akadama.
 

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