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Hydrophobicity in gritty mix

Posted by penfold2 4a, MN (My Page) on
Wed, Jun 29, 11 at 14:36

I know this has been discussed before, but the solutions don't seem to be working in my case.

About a month ago I repotted a large number of my succulents in the gritty mix. I used 2 parts Rexius fine grade orchid bark, 2 parts #2 cherrystone, 1 part Turface, and 1 part Napa Floor Dry. I noticed the plants are not doing well, so I did a little digging today (literally). I found that after watering, the soil is still bone dry just below the surface. So I tried watering, waiting 5-10 minutes, and then watering again. Same problem.

Hydrophobic soil

I've tried watering repeatedly with a hose-end sprayer, and even plugging the drainage hole and flooding the pot for 5-10 minutes. This improves the wetting somewhat, but there are still large dry pockets. Some dust even blows out when I dig around.

I don't remember having this problem with previous batches of gritty mix. Could it be due to the new bark I'm using? The Rexius bark is heat treated Douglas Fir bark. Will this problem improve over time? Should I look for a wetting agent? It's ridiculous, but I literally don't know how to get this soil wet.


Follow-Up Postings:

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RE: Hydrophobicity in gritty mix

I've had the same issues with the gritty mix, as well as the 5-1-1 mix. The bark turns hydrophobic when it dries out, and that's where the issue lies. I now water by keeping the pot in the catch tray, and using a baster to keep reapplying the water. I just recently repotted some plants into the gritty mix, but without the bark. I notice that it waters MUCH better, but mind you, I use all rain water, so my solution is acidic, which is what the bark is useful for in the gritty mix. For my succulents, which have bark in the mix, I do like you said, and plug the whole, fill with water, and wait a bit for it to soak in. I plug it with my finger, that way as I'm holding the pot, I can roll it around to make sure the water is hitting everything. I've posted on this problem before, so at least I'm not the only one who has some trouble. The 5-1-1 mix is even worse for me, to the point where I am probably not going to use it anymore, at least not in smaller pots. Large pots seem to work better though.

Joe


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RE: Hydrophobicity in gritty mix

Thanks, Joe. I have some other plants in a gritty mix which has pumice in place of bark, and these accept water much more readily. But the pumice is expensive since there's no local source. I may try replacing or eliminating the bark in future mixes. I acidify my water so I'm not too concerned about pH.

I spent the rest of the day soaking pots and they seem to be pretty well saturated now, but it was a laborious process. I'm hoping this mix improves with time because I have gallons and gallons of it in my pots, and I do not want to replace it all. I still wonder if a wetting agent would help. I'm not sure if I can find one locally.


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RE: Hydrophobicity in gritty mix

Pen,
that is the strangest thing. Maybe I've never experienced this because I've never made an exact
Gritty Mix with the granite chips. I've always substituted either quartz grit or scoria.

I think the kiln-dried bark could very well have something to do with the wetting problem.
I know we're talking succulents, and it's often best to pot with a dry mix at first,
but have you tried pre-soaking the bark?

As for wetting agents....I'm sure you could find a soap that would work.


Josh


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RE: Hydrophobicity in gritty mix

Yes, it's very strange. I'm definitely thinking it's the bark. My pumice, granite, Turface mix does not have this problem. I may try a couple drops of Dawn in my watering can next time. I've never presoaked the bark, but I'm thinking that soaking it overnight with a couple drops of Dawn might help a lot.


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RE: Hydrophobicity in gritty mix

  • Posted by tapla z5b-6a mid-MI (My Page) on
    Thu, Jun 30, 11 at 21:07

FWIW - I've never had a wetting/rewetting issue with the gritty mix - even when it's completely dry. The Turface always accepts water greedily, which then diffuses into the bark, breaking any hydrophobic tendencies. I generally water new plantings/repots twice, the second at an interval of something greater than 10-15 minutes.

Al


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RE: Hydrophobicity in gritty mix

That's how I would expect things to work, but in this case the water isn't even getting to the Turface. I don't know if you can see it in the pic, but everything is dry, not just the bark. It's like my soil has a wax coating or something. Maybe the dust from the bark is coating everything and repelling the water. I'm hoping it will improve now that I managed to saturate it pretty well, but I'll have to wait until my next watering to find out.


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RE: Hydrophobicity in gritty mix

can you fit your container inside another for a soak ?


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RE: Hydrophobicity in gritty mix

  • Posted by tapla z5b-6a mid-MI (My Page) on
    Fri, Jul 1, 11 at 11:36

Lodged way back in the depths of my memory banks, I remember reading that a polarity factor can be in play when soils become hydrophobic. That there were factors that can actually influence the alignment of Fe molecules on the colloidal surfaces and turn them hydrophobic. I'm sorry, but I have no idea where I found it or the science behind how that works, but it seems as though there's a possibility that if you can find out more, you might find your answer - can't help more than that ......

Al


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RE: Hydrophobicity in gritty mix

Thanks guys. I left the pots out in the rain tonight. I'm hoping that once I manage to saturate and flush the soil a couple times, it will become easier to wet. And I think I'm going to have to do a good job of presoaking this bark before mixing in the future.


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RE: Hydrophobicity in gritty mix

Presoaking isn't going to help you much if that bark dries out in the future. That becomes the real issue with succulents, because you must let them dry out before watering, which makes the bark hydrophobic again. But, as Al said, usually the turface readily takes up water, and will share it with the bark.

Joe


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RE: Hydrophobicity in gritty mix

I guess I'm more concerned about the dust from the bark than the bark itself. My only guess right now is that the bark dust coated everything when mixing, which turned the entire mix hydrophobic. If I can eliminate the dust by soaking, then the Turface and granite should stay wettable. Hydrophobic bark I may be able to deal with, but 100% hydrophobic soil is extremely difficult to rewet.

I'm guessing this problem is specific to the new brand of bark I'm using (Rexius), since I have not had this problem with other barks. Unfortunately, this is the only reasonably priced bark I am able to find in an appropriate size.

Joe, for your Turface/granite mix, do you use them 50/50, or some other ratio?


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RE: Hydrophobicity in gritty mix

I've not had a problem. I just searched on google and found this: http://www.geoponicscorp.com/hydrahawk-details.html

"HydraHawk is used to help water penetrate compacted or arid soils and aids plant life in the uptake of water and nutrients. HydraHawk is a natural performance-enhancing wetting and protective agent derived from fruit and vegetable extracts."


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RE: Hydrophobicity in gritty mix

penfold, the ratio depends on what is growing in it. For my succulents, I use a 1:1 turface/granite. For tropicals, I am currently using a 2:1 turface/granite mixture. I am going to also experiment with trying a 100% turface mixture in the near future, but only for plants that don't tolerate drying, like chinese evergreens. Anyway, should you choose to go this route, you MUST be very careful in how you fertilize. Without the bark, you have absolutely no buffer of nutrients. Although, from what Al says, the bark provides very little, at least there is some. Without it, there is none, so you have to fertilize at every watering, which I do anyways. Now, the bark also adds a buffer in the way of pH, bringing it down a notch, but from my readings, it is apparent that your water solution is more important in regards to pH. I have no problems, because I use 100% rain water, which is acidic, but if you use tap water, you will need to get a pH test kit, and add vinegar to your water if you have alkaline water, which most tap water is. If you do a search of "growing in turface" or "100% turface", there is some good info about this subject. It sounds like a lot of work, but it really isn't, in fact, it is less work for me because I don't have watering issues with the gritty minus bark mix. The plants growing in it are also looking real good, seemingly quite happy with their new "home", not to mention that this mix is 100% reusable.

Joe


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RE: Hydrophobicity in gritty mix

Sounds good. I'll keep that in mind if this bark doesn't work out. I already add acid and fertilizer to all my water, so that's not a problem.


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RE: Hydrophobicity in gritty mix

I also posted on this topic a while back. I do have the exact same problem: I could water with a hose all day over a hydrophobic trouble spot but it wouldn't ever absorb.

I assumed mine was more my fault since I used a smaller granite component: granite that was between #8 and #10 in size (mostly a bit bigger than #10, where it was the smallest size possible that didn't fall through insect screen). This holds more water on the exterior of each granite piece, but it does reduce the aeration in the mix: specifically the size of macro pores.

I guessed (don't know if it's true) the hardness of my water had lower elasticity/higher surface tension, which then kept it from wanting to enter the smaller pores once the bark became hydrophobic. As the water drained, it failed to entire the smaller sized macropores and avoided perching long enough to wet the bark... it would then follow the path of least resistance down the sides or a pre-wetted pathway down to the bottom of the container.

Neither the FloorDry nor the Turface particles were able to absorb water and those small gaps, once they became hydrophobic, stayed that way.

Glad to know it's not just me with the smaller granite.

I have this problem with trees that have lots of fine rootage occupying the spaces. Other trees, like "dwarf Citrus" on Trifoliate Hybrid stocks have much larger roots wherein the most water absorbing ones are relatively large at the tips of the existing roots. This isn't a noticeable problem for those trees.

The solution? Water more frequently to prevent the bark from becoming hydrophobic. The container that had the most issue last year was a Japanese Maple in Turface mix and is doing just fine this year with a bit more frequent watering.

Is that a factor? The hardness of the water?

On a similar note: I'm having the same problem with a dwarf nectarine wherein roots have now aggressively expanded and filled all air pocket space in one mix, so it "appears" to be happen again (the tiny bits of water is sucked up so quickly make it hydrophobic again). But that is a totally different reason and would likely happen in any mix.


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RE: Hydrophobicity in gritty mix

I still conclude that it is 100% the bark's fault. When you leave out the bark, the gritty mix waters easily and thoroughly. No bark for me from now on.

Joe


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RE: Hydrophobicity in gritty mix

So how would one adjust for a no-bark mix?

* Req fert every watering
* Monitor pH very closely, as there is no pH buffering.
* Container size is likely a concern now, i.e. over-potting.

I would venture a guess there is reduced aeration without the bark component, also. Therefore particle size (i.e. sifting) would be of even greater importance.

Interestingly, this all takes a big step toward hydroponic on that scale of in-ground vs. hydroponic that Al frequently judges for container care.

Is that it?


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RE: Hydrophobicity in gritty mix

Yes sir. I do fertilize every time I water, and I use 100% rain water, which comes in around 5.5 for a pH. The mix is still VERY free draining, but that assumes that you screen your ingredients, which I do. I would have to say that it's more or less "modified hydroponics", because you are still relying on the typical watering style. I am quite happy with the results so far.

Joe


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