Root behavior in porous vs. nonporous pots

Discuss repotting, soil, lighting, fertilizing, watering, etc. in this category.
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Steve Johnson
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Re: Root behavior in porous vs. nonporous pots

Post by Steve Johnson »

mikethecactusguy wrote: Mon Jan 18, 2021 1:32 pm Hi Steve
This topic has now proven itself correct. I have a tendency to use reclaimed terra pots that used to house store bought Orchids. Over the weekend I had noticed a plant leaning and decided to check it. When I unpotted it, the roots were stuck to the side of the pot and the soil was drying from the center out. This was one of these recycled cabo shaped orchid pots. I tested it and found it very porous. I'm guessing it was a cheap low fire pot.
This is the first time I have had this happen. I guess I need to check all the "cabo" pots to make sure I am not having the same issue.
Hi Mike,

Thanks for sharing your experience with us here -- it's a good opportunity to discuss how we go about selecting the right mix for growing our plants in nonporous pots. And the right mix is determined by one's local climate. First of all, we need only two basic ingredients, dirt and rocks:
  • Dirt = soil, used for water retention in the mix. Pure sandy loam soils would be ideal, but pretty much impossible to find in reality. Commercial potting soils contain a certain amount of organic material, and if we see big chunks of tree bark, pick out as much of it as you can. What we want is mostly soil with a minimal amount of organic material. Try to aim for something like this:

    Image
  • Rocks, used for drainage and proper aeration of the roots. Pumice is perfect because it also retains water. While I'm not a fan of Perlite, it retains water too, plus it's lighter than pumice. The downside with Perlite is that it's a big floaty pain in the you-know-what, but a good layer of gravel top dressing keeps it from floating away whenever you water. If pumice and Perlite aren't options, go with decomposed granite (DG) or crushed granite poultry grit. I grow the vast majority of my cacti in a pure soil-less mineral mix containing 60% pumice and 40% granite gravel, and here's what it looks like:

    Image

    That's "dirty" mineral mix on the left, and clean mix on the right. Mineral dust can become a root-clogging mess over time (a particular problem with DG), so rinse your mineral gravels thoroughly before you put them into the mix.
Now that we have our dirt and rocks, the tricky part is determining the right balance of both. Even better would be to go soil-less, although whether you can or not depends on the combination of heat and humidity in your climate.
mikethecactusguy wrote: Sun Jan 10, 2021 10:35 pmI tried sealed pots with some of the plants. I was sad to find that those were the ones that developed root rot.
Did that happen when you were still living in Benedict Canyon? If so, sealing the pots wasn't the problem -- your climate wasn't far off from mine, so you would've done well going with the same soil-less mix I've been using with great success over the last 9 years. Not so well for the hot, dry desert climate of Indio, and you'll need soil in your mix for better water retention.

To all of our members living in a desert-type climate, I have a recommendation for you -- contact Miles Anderson of Miles' To Go and ask him about the specifics of the mix he uses. If you see photos of his spread in Cortaro AZ, you'll notice something quite significant -- not a porous clay pot to be found anywhere. As you investigate the mix you should use, be sure to include questions on how he approaches watering care -- you'll learn a lot from one of the best in the cactus and succulent business. (Besides that, Miles is a great guy and willing to share his expertise with you.)
If you just want photos without all the blather, please visit my Flickr gallery.
My location: Los Angeles, CA (Zone 10b)
EliWhitney3140
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Re: Root behavior in porous vs. nonporous pots

Post by EliWhitney3140 »

wow, that was really surprising to see. Thank you for this post
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jerrytheplater
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Re: Root behavior in porous vs. nonporous pots

Post by jerrytheplater »

Shane wrote: Fri Jan 15, 2021 7:33 pm
One Windowsill wrote: Thu Jan 14, 2021 6:11 pm Whenever I repot plants from round pots there is usually a thick circle of roots at the bottom of the pot that just go round and round. In square pots they tend to go in different directions when they hit the corner so many go back into the body of the soil. Even if they are a mass, they seem to be less packed together.
Hmm very interesting. Think you're onto something here. What's your experience with Square pots with rounded corners?

I'd like to learn more about this and think I'll do an experiment. I'll plant a bunch of uprooted Aloe cuttings in different pots then later dig them up and see how the roots look. I'm choosing Aloe because they get root bound easily (seems like the roots take like 2 laps around the pot then head straight out of the bottom ](*,) ), and because people give away lots of Aloe they trimmed back in their yard at my local CSS (so I can get lots of cuttings of the same plant). (Note that in person meetings are suspended indefinitely so I probably won't be able to do this for a while)
I know I'm new here on the forum, but I can chime in here from what I've seen in a commercial greenhouse near me. They had a special liner made for growing tree seedlings where they had slits down the edges along the depth. I forget the exact depth, but it was maybe 12" or so. This prevents the roots from growing around inside the cell. When the root hits the air it stops trying to grow around the pot.

Also, I just read an article in a North American Rock Garden Society booklet: Handbook on Troughs. The article was first published in their journal. It is called "Soils for Troughs and Other Containers" by Jim Borland. It is on page 113 in this link to the journal: https://nargs.org/sites/default/files/f ... 2_NO_2.pdf I was very surprised at this article and it didn't even cover a single recipe for a soil mix. He goes into drainage and how it is affected by the potting mix texture and size distribution of the particles. I really learned a lot.
Jerry Smith
Bloomingdale, NJ
45 inches (114 cm) rain equivalent per year, approx. evenly spread per month
2012 USDA Hardiness Zone 6b: -5F to OF (-20C to -18C) min.
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mikethecactusguy
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Re: Root behavior in porous vs. nonporous pots

Post by mikethecactusguy »

Hi All
To me, a trough is just an elongated pot. Yes, no?
Mike M
Mike The Cactus Guy
Enjoying the Spines
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jerrytheplater
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Re: Root behavior in porous vs. nonporous pots

Post by jerrytheplater »

Mike, absolutely!!
Jerry Smith
Bloomingdale, NJ
45 inches (114 cm) rain equivalent per year, approx. evenly spread per month
2012 USDA Hardiness Zone 6b: -5F to OF (-20C to -18C) min.
DaveW
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Re: Root behavior in porous vs. nonporous pots

Post by DaveW »

Hi Mike,

The different behaviour of soils in pots to open ground has been discussed before and I reproduce some of the relevant links here:-

http://oregonstate.edu/dept/nursery-wee ... rties.html

https://www.youtube.com/watch?v=ego2FkuQwxc

Interesting your article says you need 2ft deep containers before it behaves as garden soil does.

I have not yet found 2ft deep pots, but did start trying widely spreading offsetting plants in standard full depth pots (the standard UK pot is usually same height as width) instead of the shallow pans they are usually put into and the plants seem to prefer it. It is a myth that shallow pans dry out quicker around the roots than in full depth pots since due to the perched water table the reverse is often the case. Also different strata in a pot are an inhibition to drainage, including a layer of gravel in the bottom and are not an aid to drainage as the video shows.


Dolichothele longimamma in full depth pot.

longimamma.jpg
longimamma.jpg (100 KiB) Viewed 12498 times
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jerrytheplater
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Re: Root behavior in porous vs. nonporous pots

Post by jerrytheplater »

Hi Dave

Beautiful plant and well grown. And thanks for the links to the James Altland articles. Very helpful. I've saved them for future reference. And I am trying to search the forum for topics before I post, but, I am not perfect. I hate to be the one that asks the question which has been discussed for years.

The author of the article on soils for troughs was not suggesting we should be using 2 foot deep pots. I have not seen any that deep either, unless it is a trough. He was saying that for container soils to behave like natural soils in regard to drainage, they would need to be at least 2 feet deep. For me, that answered why I would not be able to grow plants in pots well in soil that I dug up from my garden. I've always wondered about that.

Here's where the author gives the 2 foot plus container depth suggestion.
"This effect of water held at the interface between the bottom of the soil and the container bottom creates what some call a perched water table, and it occurs in any container of any depth and width . Not until the container depth exceeds 2 feet do the air and water characteristics of the soil contained begin to simulate those found in the garden."
Jerry Smith
Bloomingdale, NJ
45 inches (114 cm) rain equivalent per year, approx. evenly spread per month
2012 USDA Hardiness Zone 6b: -5F to OF (-20C to -18C) min.
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One Windowsill
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Re: Root behavior in porous vs. nonporous pots

Post by One Windowsill »

I have seen Welwitschia mirabilis grown in pots that looked like chimney pots.
DaveW
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Re: Root behavior in porous vs. nonporous pots

Post by DaveW »

Welwitschia's are not Succulents, in fact they have a very long taproot that goes down up to 30 feet, some even claiming 70 feet, therefore they are really "plumbed in" to the deep water table that often exists even in many arid areas.

https://hscactus.org/resources/plants-o ... chia-2017/

http://www.columbuscactusclub.com/welwi ... bilis.html

https://succulent-plant.com/families/we ... iales.html

I gather that some manage to grow them OK though even if they don't have 30ft deep pots. Instead of pots some use a length of clay drainpipe but presumably plastic would do as well and be easier to cut to length?
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One Windowsill
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Re: Root behavior in porous vs. nonporous pots

Post by One Windowsill »

Ernst van Jaarsveld, who has looked after the succulents at Kirstenbosch since 1976 and who has been successfully cultivating welwitschias in this time, regards Welwitschia as a terminally truncated caudiciform, although initially semi-succulent, woody xerophyte.
http://pza.sanbi.org/welwitschia-mirabilis
fanaticactus
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Re: Root behavior in porous vs. nonporous pots

Post by fanaticactus »

I'm another fan of plastic pots after multiple deaths of cacti in clay pots. Plus, when it comes time to repot, I found the roots had adhered to the inside of the pot! If I absolutely must use a clay pot--because of size & shape to accommodate certain cacti--I use a waterproofing that can be applied to the inside. Thompson's makes one I know of.
Catch a falling star--but don't try it with a cactus!
Mrs.Green
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Re: Root behavior in porous vs. nonporous pots

Post by Mrs.Green »

An interesting topic no doubt 🙂 Steve-O wrote; ‘ Was there a better air/soil mix along the pot walls than internally? ‘ I am wondering about the same. Could it possible be that the roots are seeking out the best aerated area in the pot? In a non glazed terracotta pot it would likely be the pots walls?
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Re: Root behavior in porous vs. nonporous pots

Post by fanaticactus »

Mrs.Green wrote: Thu Jul 14, 2022 7:50 pm An interesting topic no doubt 🙂 Steve-O wrote; ‘ Was there a better air/soil mix along the pot walls than internally? ‘ I am wondering about the same. Could it possible be that the roots are seeking out the best aerated area in the pot? In a non glazed terracotta pot it would likely be the pots walls?
I believe that's the answer. Any mixture should be uniform throughout the pot. I imagine the roots can sense the porosity of the sides and that's why they are attracted to them.
Catch a falling star--but don't try it with a cactus!
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greenknight
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Re: Root behavior in porous vs. nonporous pots

Post by greenknight »

The porous pots absorb moisture and dissolved nutrients, I thinks that's what attracts the roots.
Spence :mrgreen:
Mrs.Green
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Re: Root behavior in porous vs. nonporous pots

Post by Mrs.Green »

fanaticactus wrote: Thu Jul 14, 2022 8:29 pm
Mrs.Green wrote: Thu Jul 14, 2022 7:50 pm An interesting topic no doubt 🙂 Steve-O wrote; ‘ Was there a better air/soil mix along the pot walls than internally? ‘ I am wondering about the same. Could it possible be that the roots are seeking out the best aerated area in the pot? In a non glazed terracotta pot it would likely be the pots walls?
I believe that's the answer. Any mixture should be uniform throughout the pot. I imagine the roots can sense the porosity of the sides and that's why they are attracted to them.
greenknight wrote: Thu Jul 14, 2022 10:16 pm The porous pots absorb moisture and dissolved nutrients, I thinks that's what attracts the roots.
Thanks for contributing Fanaticactus and Greenknight 🙂 couldn’t it be a combination of that factors as well?
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