Injecting Gels Into The Soil — Good Idea?

It recently came to my attention that the Sierra Club published an article on a new system for reducing watering in lawns.  You can read it here.  Basically what the company, AquaCents, does is inject a polyacrylamide gel into the landscape and then the gel supposedly collects irrigation and/or rain water and releases it for plants to take up as the landscape dries.

I think it’s a good concept, but I’m highly skeptical that this is a good product for two reasons.  The first is that I’ve used polyacrylamide gels to hold water for plants before and have found no benefit.  In fact, most papers out there on the topic show either no benefit or marginal benefit from using these gels in terms of increasing the amount of water available to plants – though I must admit that results are variable.

Please note that I didn’t say I was skeptical that the polymer will hold lots of water – I’m not.  It will hold lots of water.

Which leads us to an important question.  If we know that the gel will hold water, and this company has done testing which shows reduced watering is required in lawns that use this technology, then why am I skeptical?

Based on what I have read and the experiments I’ve done, I think the company’s testing isn’t telling the whole story.

As far as I can tell, what they’re doing to test this product is injecting it into lawns and then allowing a moisture detector in the lawn to trigger sprinklers to go on when soil moisture falls below a certain level.  If you test one lawn with the polymer side by side against another lawn without the polymer, then the lawn with the polymer will use less sprinkler water because the gel holds more water than the surrounding soil – meaning that it stays more moist. So at this point it sure seems like the gel is a good idea — right?

No, because this experiment asked the wrong question.  It looked at how much water was in the lawn, NOT HOW MUCH WATER WAS GETTING TO THE PLANT.  And that’s what we need to know – how much water gathered up in that gel will actually get to the plant.  What I’ve found in my work is that having water in the gel is not the same as getting water to the plant.  The gel seems to hold the water too tightly for the plant to get it.  It’s a little like having an impenetrable safe filled with five million dollars in gold.  Sure, the gold is there, but if you can’t get to it, who cares?

So, why does the grass seem to be growing more roots when the gel is used?  My best guess is that the lawns were overwatered in the first place and the gel just provided a way for homeowners to decrease their watering.  Let’s face the facts, overwatering of lawns is rampant.

But I mentioned that there were two reasons why I didn’t like the gel.  I named the first, so what’s the second?  It’s something that I saw on one of Linda’s sites a few years ago and then looked into a little further.  Polyacrylamide gel, while relatively safe in and of itself, may break down into more toxic substances.  See Linda’s article here.

Finally – and this is just a thought — there are plenty of other absorbent materials out there that might be injected into the ground, including some made of starch – I have tried gels made of starch and have found them to be as effective as those made of polyacrylamide (though I know that’s not saying a lot).  Or…maybe we should just water more judiciously.  Like I said, just a thought.

14 thoughts on “Injecting Gels Into The Soil — Good Idea?

  1. Nice catch, Jeff. And just to add more fuel to the discussion, as the gels dry out they pull water AWAY from the roots. Not good. Furthermore, work with gels and tree roots show that roots grow less with the hydrated gels, presumably because they don’t have to explore the soil for more water.
    Shame on Sierra Club for not doing their homework.

  2. It’s interesting that you bring this up, because I just got back from the ESA meeting and one of the vendors was touting a gel-based “watering solution”. They had free samples, so I’m interested to see whether it actually works on my houseplants.

    On the other hand, said experimental plant is E. aureum, so I might not notice even if it doesn’t work!

  3. Speaking of watering, are those moisture meters at the hardware store any good? I’d like my watering of beds to be a little more refined.

  4. Absolutely not. This is yet another desperate attempt to force unnatural and wasteful “immaculately green lawns” down America’s collective throat. We need to move away from that nonsense, not figure out even more dubious ways to cling to it.

    Also, why on earth would any one pay a company to do this when they could simply buy the desiccated gel themself and apply it as needed? I did that with some potted plants and it worked fine. I would not use this on any plants I intend to eat, though.

  5. Hmmmmm, “roots grow less well because they don’t have to “explore” the soil for more water?” You make it sound as though roots wear little mining helmets with lanterns, Linda. It’s like saying tree roots “seek out” sewer lines when nothing could be further from the truth. Please correct me if I’m mistaken, but I don’t think roots “explore” anything. They’re totally opportunistic and proliferate wherever soil conditions (moisture, atmospheric, chemical, biological, etc.) are suitable. I think it’s important to constantly strive to precisely describe how plants function.

  6. Terry, “explore” is a perfectly valid word to describe what roots do, and it’s commonly used in the scientific literature (and indeed is used in the article I was citing). It has no anthropomorphic connotation. They grow wherever they can, and if they end up in a nutrient/water/air deficient environment, those active root tips stop growing and energy is funneled elsewhere.

  7. Let me see if I understand… If grass is lightly watered frequently, the roots will only/primarily grow in the top layer of soil. (I knew that part.) If the top layer is allowed to dry between thorough waterings but the deeper layers of soil stay moist, the surface roots in the dry layer stop growing and the grass plant sends other roots down deeper, simply because there is no moisture in the top layer. Is that correct or am I missing something? This is excellent information to help homeowners (and me!) understand the reasons for twice a week deep irrigation instead of every day or two. All of that said, would two waterings of about ½” each over two back to back days, then wait five days to allow the top layers to dry more, be better than separating the watering schedule by several days? Just a thought…

  8. Hi Sandy, I think you’ve got it basically right. I don’t think the 1/2 inch watering over two consecutive days will get deep enough during hot summer days though. And I’ve gotta tell ya — I don’t believe in watering more than once a week — In fact, I don’t water my lawn at all and just let it go dormant. Deep watering once a week probably won’t give you a lush lawn, but it should be healthier with deeper roots

  9. Thanks, Jeff. I don’t water our lawn either, but a lot of the clients we talk to want to know the best way to use their existing irrigation systems. Far too many think that every day during the heat of summer is the answer. That is, if they aren’t under water restrictions. Then they will water every day they are allowed, usually every other day, odd/even house number schedules. Lawns seem like such a waste to me anyway. I think they should all be converted to cottage gardens!

  10. I’m sure there are some poor spas that will fall for this. I suppose there was no indication if this material appeared on the surface and children or pets would happen to consume it what the consequences would be? To change the subject your thoughts on Zeba quench?

  11. We have used Zeba before — with mixed results. I think it has a better shot of working than the polyacrylamide gels.

  12. Thank you for covering this. I used “Soil Moist” in my hanging baskets this year, which is a “starch-grafted polymer” according to their MSDS sheet. As for results I’m not sure how much it helped, but my flowers did make it through an unusually hot summer without daily waterings.

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