Author Topic: Substrate and water retention  (Read 14560 times)

Markyscott

  • Legit New User
  • *
  • Posts: 38
Substrate and water retention
« on: November 30, 2012, 12:24 AM »
I thought I'd share the results of a little semi-scientific experiment I carried out. Substrate composition is one of those topics around which there is a tremendous amount of lore, and sorting out meaningful information can be somewhat challenging.  Like many of us, I switched to a inorganic substrate a number of years ago.  But living in a very hot climate and using a soils with low water retention means frequent watering (three times a day in the summer).  I've been very happy with the results, but the hobby has definitely become more of a lifestyle choice than a pass time.  That's not a complaint, but I've become sensitive over the years about water retention.  I had questions, lots of advice, and very few facts:

What inorganic substrate is the most water retentive?
How does grain size influence the amount of water retention?

I purchased several 500 ml beakers and drilled a small hole in the bottom of each:

 

Markyscott

  • Legit New User
  • *
  • Posts: 38
Re: Substrate and water retention
« Reply #1 on: November 30, 2012, 12:30 AM »
I selected the following substrates:

1) Pumice (Wee Tree domestic pumice)
2) Akadama (Double Line)
3) Turface (MVP)
4) Seramis

I sieved each to the following size fractions:

>1/2", 1/2"-3/8", 3/8"-1/4", 1/4"-1/8"

Here's an example of the pumice fractions:

« Last Edit: November 30, 2012, 12:59 AM by Markyscott »
 

Markyscott

  • Legit New User
  • *
  • Posts: 38
Re: Substrate and water retention
« Reply #2 on: November 30, 2012, 12:35 AM »
I filled the beaker with 500 ml of the sieved substrate and poured through 500ml of water (red color is food coloring to help see the water better), measuring the amount that drained out the other end.  The water that fails to drain measures the field capacity (the saturation after the gravitational water has drained away).  Here's an example:



 

Markyscott

  • Legit New User
  • *
  • Posts: 38
Re: Substrate and water retention
« Reply #3 on: November 30, 2012, 01:14 AM »
Here are the results for pumice.  As you can see, the saturation exceeds 23% for the finest grained fraction I tested (1/4-1/8") and decreased wtih increasing grain size to 10% for the coarsest fraction I tested.  When I repeated the test with the same soil, 500ml drained through, a result I interpreted to indicate that the substrate had reached its field capacity on the first watering.

 

Markyscott

  • Legit New User
  • *
  • Posts: 38
Re: Substrate and water retention
« Reply #4 on: November 30, 2012, 01:29 AM »
Here are the results for the 3/8"-1/4" size fraction for the various inorganic substrates.  Seramis was by far the most water retentive at 30% saturation field capacity.  Turface, akadama, and pumice were similar at about 13% saturation field capacity.  I tested decomposed granite as well - as long as it was rinsed thoroughly it had very low water retention (~6%).
« Last Edit: November 30, 2012, 01:36 AM by Markyscott »
 

Markyscott

  • Legit New User
  • *
  • Posts: 38
Re: Substrate and water retention
« Reply #5 on: November 30, 2012, 01:41 AM »
Please don't take any of this as an endorsement for any particular brand or soil mix - I wouldn't presume.  But I believe the results suggest a couple of things that were interesting to me:

1) Increasing the fraction of fresh akadama will not appreciably increase the water retention of the soil (unless you're replacing granite).  I understand that akadama breaks down over time and so it's likely that there will be a concommitant increase in water retention as the soil "ages".  These results don't speak to that.

2)  Based on these results alone, if you want a more water retentive mix, one might consider adding Seramis as a component or consider sieving to a finer grain size.  Both of these factors seem to make a pretty big difference in terms of water retention.
 

Owen Reich

  • Hero Forum Member
  • *****
  • Posts: 888
  • Thanked: 7 times
Re: Substrate and water retention
« Reply #6 on: November 30, 2012, 07:28 AM »
Nice project  ;D.  Now you only have to do 5000 more repetitions using different components in various ratios to find "the perfect" one.....  I've never used Seramis.  What is it designed for?

The real kicker is how much each tree takes in in a given season and how to compromise on a mix that works all year where you live.  Where I study, we go for faster draining mixes; there are also apprentices here who check water sometimes 5 times a day and water any given tree 1-3x a day.  It must be nice having "watering drones" as Mike Hagedorn calls them. 

Those tests are a very nice start.  Different containers have different zones of saturation and some pots (especially old Chinese pots and converted suibans) tend to keep more water in the bottom. 

I look forward to hearing more of your results.  It would be great if you combined different components and see how it affects the results. 
 

Judy

  • Hero Forum Member
  • *****
  • Posts: 631
  • Thanked: 2 times
Re: Substrate and water retention
« Reply #7 on: November 30, 2012, 07:30 AM »
Thanks for this experiment,  I've never heard of Seramis?  I'll go google it...

I would also be interested in seeing haydite as one of the components tested, as I've recently started mixing that into my soil mixes.

Do you know how CE rates compare?  This is of as much importance (IMO) as the water retention.
 

Markyscott

  • Legit New User
  • *
  • Posts: 38
Re: Substrate and water retention
« Reply #8 on: November 30, 2012, 07:49 AM »
Nice project  ;D.  Now you only have to do 5000 more repetitions using different components in various ratios to find "the perfect" one.....  I've never used Seramis.  What is it designed for?

The real kicker is how much each tree takes in in a given season and how to compromise on a mix that works all year where you live.  Where I study, we go for faster draining mixes; there are also apprentices here who check water sometimes 5 times a day and water any given tree 1-3x a day.  It must be nice having "watering drones" as Mike Hagedorn calls them.  

Those tests are a very nice start.  Different containers have different zones of saturation and some pots (especially old Chinese pots and converted suibans) tend to keep more water in the bottom.  

I look forward to hearing more of your results.  It would be great if you combined different components and see how it affects the results.  

Seramis is a German fired clay product designed for plants - http://www.seramis.com/.  Its $17 for 7.5L.  There are some videos posted on their site of a similar experiment to what I undertook here.  It's where I got the idea for doing this.  And to do 5000 more tests - yikes - I'd need my own set of watering drones!  I just have 4 kids and a wife who all think I'm a bit off and want no part of my beakers and ziplock baggies filled with gravel.  

In the summer here our climate is pretty tropical - it gets to one thousandty degrees outside (according to my daughter). And the only creatures that seem to like it are the mosquitoes.  During that time, water retention in the soil is a concern for us working folk whose employers frown on their employees taking off every few hours to water our trees.  In the heat of the summer I water before I go to work, have a sprinkler that comes on at mid-day, and water again in the evening - it's usually pretty dry by then.  The good news is that summer only lasts 14 months per year.

Also, its interesting that you mention pots.  I''ve started to look at water retention as a funtion of the pot shape.  I haven't finished that yet, but directionally it appears that an equivalent volume of soil has a higher field capacity in a shallow pot than it does in a deeper pot.  It also appears that adding a drainage layer has the same effect (it makes the mix more water retentive).  I'll post more on that later.  Not sure why old Chinese pots in particular would make a particular difference - if you send me a few, I'd be happy to test them for you!

I have tested some mixes as well - I'll post those results later.

Scott
« Last Edit: November 30, 2012, 08:25 AM by Markyscott »
 

Markyscott

  • Legit New User
  • *
  • Posts: 38
Re: Substrate and water retention
« Reply #9 on: November 30, 2012, 08:06 AM »
Thanks for this experiment,  I've never heard of Seramis?  I'll go google it...

I would also be interested in seeing haydite as one of the components tested, as I've recently started mixing that into my soil mixes.

Do you know how CE rates compare?  This is of as much importance (IMO) as the water retention.

Not sure what you mean by CE rates.  Are you referring to cation exchange capacity (CEC)?

Also - haydite is on my list.  I'm a little low on it now and couldn't get enough after sieving to test all the size fractions.  I have to wait to make another trip to the nursery to restock.  Directionally, it looked as though it has a bit lower field capacity than the other fired clays (seramis, akadama, and turface).

Scott
« Last Edit: November 30, 2012, 08:34 AM by Markyscott »
 

Judy

  • Hero Forum Member
  • *****
  • Posts: 631
  • Thanked: 2 times
Re: Substrate and water retention
« Reply #10 on: November 30, 2012, 09:47 AM »
Yes I was meaning CEC. 
I did a test between haydite and turface this summer, it wasn't as practical as yours however.  I measured equal cup size amounts, added equal amounts of water to each (done in buckets not in a pour thru situation), then I compared the dry weight of each sample with the wet weight after I drained them for an equal amount of time.  The turface was a bit more water retentive, but only slightly by my test.  I was looking for comparison results with your method.  Please post them if you do another test. 
 

Markyscott

  • Legit New User
  • *
  • Posts: 38
Re: Substrate and water retention
« Reply #11 on: November 30, 2012, 10:37 AM »
Yes I was meaning CEC.  
I did a test between haydite and turface this summer, it wasn't as practical as yours however.  I measured equal cup size amounts, added equal amounts of water to each (done in buckets not in a pour thru situation), then I compared the dry weight of each sample with the wet weight after I drained them for an equal amount of time.  The turface was a bit more water retentive, but only slightly by my test.  I was looking for comparison results with your method.  Please post them if you do another test.  

I've not had CEC measured myself, but I've references from publications that I can pass along.  My memory is that, although there is some variability, CEC is pretty low (relative to organics) for the components that I reported on here.  

When one increases drainage one must water a lot.  When one goes with all inorganics one must fertilize a lot.  Of the two, watering is my biggest issue because it must be done multiple times a day in the summer and if I miss a day or two, plants die.  Fertilizing is less critical for me because I can work it in around my schedule and if I miss it once or twice I don't have to attend to any funerals.

Cheers
Scott
 

Chrisl

  • Hero Forum Member
  • *****
  • Posts: 897
Re: Substrate and water retention
« Reply #12 on: November 30, 2012, 10:47 AM »
<it gets to one thousandty degrees outside (according to my daughter). And the only creatures that seem to like it are the mosquitoes....The good news is that summer only lasts 14 months per year.>

Having lived in Houston for over ten years, I can attest to this...very funny Scott!

And Thanks for posting your results, quite interesting results at that.  Nice to know Turface and Akadama are about the same. 
 

Yenling83

  • Sr. Forum Member
  • ****
  • Posts: 321
Re: Substrate and water retention
« Reply #13 on: November 30, 2012, 10:52 AM »
Thanks for the post! very interesting.  I'd imagine Double Red Line Akadama would hold more and more water as it breaks down-but that's just a guess.  I would have also guessed that fresh Akadama would have still held more water than turface.  I'd be interested to see where lava compares with the rest. 

So can you not set your sprinklers to water another time during the day when your at work?   
« Last Edit: November 30, 2012, 10:54 AM by Yenling83 »
 

sekibonsai

  • Legit New User
  • *
  • Posts: 18
Re: Substrate and water retention
« Reply #14 on: November 30, 2012, 11:17 AM »
Are you sourcing seramis locally or do you order it online?